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Regents Physics Wells Mechanics - HW Assignments Kinematics – HW01-12 - Speed, Velocity, Vectors, Acceleration, Free Fall, Graphing Motion, Projectiles Dynamics - HW14 - HW23 - Newtons laws, Circular, Gravitation Work/Energy - HW24-HW26 - Work-Power-Energy & Conservation Impulse/Momentum - HW27-28 - Impulse & Momentum NOTE: All HW should be done on loose-leaf to be turned in. It should be stapled before you enter the classroom and is due at the beginning of the period. No late HW accepted. It should NOT BE SQUEEZED into the small spaces within this packet. You do not need to rewrite questions, but your work should be on loose-leaf. Graphs and diagrams done in this packet can be attached to your loose-leaf. Your work should be neat, organized and clear as done in class and should have formulas with substituted values and units on all numbers. You will lose points for work that does not meet these criteria. Quiz: as indicated in class, you will be quizzed often on these HW problems. Physics HW #1 PAGE 1 of 1 Homework assignments can be downloaded from the website if needed http://wells.xroad.com A. Express the following in standard Scientific Notation form and E notation 1. -32.74 million dollars 2. 1744000000000 tacos 3. 0.000026006 nm B. Convert the following scientific notation numbers into common form 1. 5.6 x 105 ft 2. 3.574 x 10-5 in 3. -2.154e9 lbs 4. 3.05404e-3 kg C. Solve the equations shown below by plugging in the assigned values. Write out the operation you will perform in E notion form. Then complete the operations using a calculator, and state answers in scientific notation form. Put a ‘distance’ type unit of your choice on each answer 1. X = -3.6 x 10-24 Y = -3.6 x 10-26 X+Y 2. X = -7.612 x 1019 Y = 3 x 107 X2 * Y 3. X = -5.09 x 10-13 Y = 6 x 1016 X / Y2 D. Solve the following equations for the unknown variable; put a ‘time’ type unit of your choice on each answer (show work) 1. - t2 + 81 = 0 2. 6t+ 16 = 20 3. a = 49 ANSWERS A1) -3.274x107 or -3.274e7 dollars, A2) 1.744x1012 or 1.744e12 tacos, A3) 2.6006x10-5 or 2.6006e-5 nm B1) 560000 ft, B2) 0.00003574 in, B3) -2154000000 lbs, B4) 0.00305404 kg C1) -3.64x10-24 m, C2) 1.74x1047 in, C3) -1.4x10-46 ft D1) t = 9 sec, D2) t = 0.667 min, D3) a = 2401 hr Physics HW #2 PAGE 1 of 2 A.) Conversions – on a separate piece of paper, perform the following conversions using the factor label method. 1) 0.0000001326 m to a) m b) nm c) mm 2) 3) 4) 5) 6) 7) 8) 50 nm to mm 200 s to s 2x10-8 mm to nm 1.53 kg to g 3x106 Ms to sec 5x10-8 nm to pm .000015 Tg to kg B.) Solve the following triangle problems for the unknown sides. The angle that appears to be a right angle actually is. C.) Find all unknown angles in the triangles below. The angle that appears to be a right angle actually is. 1. 1.) 1 22 in x 22.9 m 2 17 in 2. 53.4 m x = 14.3 29 mm 1 = 67.42 2.) y 8.75 m 3.36 m 3. 2 50.4 in 78.4 cm y 3.) 2 13.2 ft 1 10.8 ft Answers A: 1a) 0.1326 m, 1b) 132.6 nm 1c) 0.0001326 mm, 2) 5x10-5 mm, 3) 2x10-4 sec, 4) 2x10-2 nm, 5) 1530 g, 6) 3x1012 sec, 7) 5x10-5 pm, 8) 1.5x104 kg B: 1) 27.8 in, 2) x=117.4 mm, y =113.8 mm, 3) y=101.2 cm or 39.84 in C: 1) 66.8°, 23.2°, 2) 22.6° 3) 35.1°, 54.9° PAGE 2 of 2 D) Graphing 1) Using the information in the table, construct a graph of Force vs Elongation on the grid. A) Label each axis with the appropriate physical quantity and unit B) Plot the data points for period versus pendulum length. C) Draw the best-fit line or curve for the data graphed D) Find the slope of the line 2) Using the information in the table, construct a graph on the grid. A) Label each axis with the appropriate physical quantity and unit. B) Mark an appropriate scale on each axis. C) Plot the data points for period versus pendulum length. D) Draw the best-fit line or curve for the data graphed. E) Using your graph, determine the period of a pendulum whose length is 0.25 meter. ANSWERS 1) Best fit line is linear, Plot point 0,0 and make sure its ‘best fit’ not connect the dots, d) = 4 N/m 2) Best fit line is a curve, do NOT connect 0,0 e) 1 sec Physics HW #3 PAGE 1 of 1 HW3 1.) A human hair is approximately 45 μm in diameter. Express this diameter in m. 2.)The distance between the sun and the earth is about 1.5 x 1011 m. Express this distance in km and in Gm. 3.) Heather and Matthew walk eastward with a speed of 0.58 m/s. If it takes them 34 min to walk to the store, how far have they walked in meters. 4.) What is the shortest possible time that a bug could drift across a bowl of water with a diameter of 6.3 cm if the bug was moving at a constant speed of 3.5 mm/sec. 5.) An athlete swims from the north end to the south end of a 40 m pool in 16 s and makes the return trip to the starting position in 22 s. (a) What is the average velocity for the first half of the swim (b) what is the average velocity for the second half of the swim (c) What is the average velocity for the roundtrip (d) What is the average speed for the roundtrip 6.) A runner travels 10 m east, the travels 4 m west. a) What is his total distance travelled b) What is his displacement for the trip. 7.) Two cars are traveling east on a desert road separated as shown in the diagram below. After 5 seconds they are side by side at the next telephone pole. The distance between each pole is 35 m. Find (a) the displacement of car A after 5 sec, (b) the displacement of car B after 5 sec, (c) the average velocity of car A during 5 sec, (d) the average velocity of car B during 5 sec. Initially BEFORE pole1 pole2 5 sec later AFTER pole3 Car A Car B pole1 pole2 pole3 Car A Car B 8.) An object moves halfway around the spherical earth (earth has a known radius that is given on the reference table, assume it is circular allowing you to use circle formulas). It takes this object 1 day to cover the distance travelled halfway around the earth. (a) What is the average speed of this object (in m/s) (b) What is the average velocity of this object. (Be sure to make a sketch and label the displacement as well as distance) 9) A high-speed train in Japan travels a distance of 300 kilometers in 3.60 x 103 seconds. What is the average speed of this train in m/s? HW3 Answers – 1) 0.000045 m, 2a) 1.5x108 km b) 150 Gm, 3) 1183.2 m, 4) 18 s, 5a) 2.5 m/s south b) 1.82 m/s north c) 0 d) 2.105 m/s, 6a) 14m, 6 m east, 7a) 35 m east, 70 m east, 7 m/s east, 14 m/s east, 8a) 231.62 m/s, b) 147.45 m/s across the earth, 9) 83.3 m/s Physics HW #4 PAGE 1 of 1 1.) Sally travels by car from one city to another. She drives for 30 min at 65 km/h, 12 min at 80 km/h, spends 10 min eating lunch and then travels 45 min at 25 km/h. Determine the average speed for the entire trip (in km/hr). 2.) The average speed of an orbiting space shuttle is 25800 km/h, The shuttle is orbiting at a radial distance of 6690 km measured from the earth center. a) Determine the time required for it to circle earth in hrs. b) What was the average velocity of the shuttle over one full orbit. 6690 km 3.) A bacteria moves 30 mm across a Petri dish at a speed of 1.25 nm/sec. How long, in hrs does it take the bacteria to move across the dish 4.) Two students walk in the same direction along a straight path, at a constant speed – one at 0.7 m/s and the other at 1.72 m/s. Assuming that they start at the same point and the same time, how much sooner does the faster student arrive at a destination 780 m away? 5) A car travels 90 meters due north in 15 seconds. Then the car turns around and travels 40 meters due south in 5.0 seconds. a) What is the magnitude of the average velocity of the car during this 20 second interval?, b) What was the average speed over the 20 seconds? 6) For the following data, make a graph of distance vs. time Time (s) 5 10 15 20 25 Distance (m) 1.5 4.8 5.5 7.6 11 a) Label your axis b) Draw a best fit line c) Calculate the slope d) What does the slope represent, and why? HW4 Answers – 1) 41.6 km/hr, 2a) 1.63 hrs, b) zero, 3) 6666.67 hrs, 4) 660.8 sec, 5a) 2.5 m/s north, b) 6.5 m/s 6) Best fit is linear, do NOT connect 0,0 c) 0.44 m/s, d) it’s the velocity since its distance over time. Physics HW #05 PAGE 1 of 1 HW5 Questions 1.) For the quantities below, define each as a vector or scalor (a) the acceleration of a plane (b) the number of passengers on a plane (c) the time required to complete the flight (d) the displacement of the flight (e) the fuel needed for the flight 2.) Can two vectors with unequal magnitudes have a resultant of zero? Explain 3.) How is the equilibrant found? 4.) What is another way of saying 30 km/hr @ 30° north of east (give the alternate direction). Sketch the vector and label the angle on your sketch. 5.) Three vectors are shown, sketch the resultant of these three vectors if they were added 6.) In the diagram below, vector R represents the resultant of vectors x and y. Draw vector y (In other words, determine the vector that you would need to add to vector x in order to make vector R) x R 7.) The vector below is drawn using a scale 1 cm = 3 m/s. Use a ruler and a protractor to measure and state the magnitude and direction of the vector. (extend the length of the vector so you can accurately read it N 8.) Vectors n = 5 m/s east, m = 12 m/s south. (a) Determine n + m mathematically (b) find the equilibrant for the answer to (a) 9.) A fox runs 8 m heading 25° north of west and then turns and heads west 4 m. Determine the fox’s displacement graphically (note that displacement is a vector quantity). 10.) A taxicab heads north 4 km on 1st st. and turns west onto 51st st. He heads west 1.5 km on 51st st and turns south on lex. The cab finished his fare by traveling 2 km south on lex. Mathematically determine the displacement of the cab (note: a right triangle is formed as a result of the 4 movements) HW5 – Answers 1) vector, scalar, scalar, vector, scalar, 2) No, cant cancel if unequal, 3) it’s the opposite of the resultant, 4) 30 km/hr @ 60° E of N, 5) redraw each and link head to tail, gives arrow pointing up-right for resultant, 6) y points up and right, 7) measured (2.5cm) = 7.5 m/s @ 22° N of E, 8a) 13 m/s @ 67.4° S of E, b) 13 m/s @ 67.4° N of W, 9) 11.8 m @ 17° N of W, 10) 2.5 km @ 53.13° N of W Intentional Blank Page Intentional Blank Page Physics HW 6 PAGE 1 of 2 Beginning with this HW assignment, HW’s will be given in 2 parts. This handout is part A of the HW. Part B of the HW will be multiple choice problems assigned from the castle learning website. These multiple choice problems are due the same day this HW is due and will count as part of the grade and will also be potential HW quiz questions. HW6A Questions 1. Three student combine two vectors with magnitudes of 55 and 25 units each and each get different answers of 85, 20 and 55 units. Explain which answer is correct and why. 2. Can a vector have a component equal to zero without being zero itself? Explain with an example. 3. What are the x and y components of a vector Va = 50 mph 10 east of north 4. The x component of a vector is 5 m West. The y component of this vector is 25 m North. What is the vector that has these components. 5. What are the x and y components of a vector K = 400 km/hr @ 75 west of south. 6. Vectors are defined as: Determine (a) A - B (b) 2*B - A A = 3 m east B = 7 m north 7. A boat in still water travelling at 40 m/s east enters a stream with a current of 15 m/s north. A) What is the resultant velocity of the boat in the water (Solve both graphically and mathematically and show each). B) If the stream is 100 m wide, how long does it take the boat to cross? 8. Birds fly to their destination using the following paths: 300 km N, 100 km E, 500 km @ 65 W of N. Sketch the vector picture and solve for the resultant displacement graphically. 9. Two vectors G=10 ft @ unknown angle and H=14 ft @ unknown angle are to be added to each other to get a resultant vector. What is the maximum and minimum possible value of this addition? Be sure to show sketches of the two situations where you get the maximum and minimum. 10. A storm travels to a destination in two parts. In part I the storm travels south at 25 km/hr for 0.75 hrs and then turns and travels in section II at 41 km/hr @ 30° east of south for 1.2 hrs. (a) Determine the displacement of each separate section of the trip, (b) Graphically, determine the total resultant displacement of the storm. 11. A plane travelling at 250 m/s north in still air enters a crosswind of 75 m/s west. a) What is the resultant velocity of the plane. b) If the 75 m/s was a tailwind directed north, what would the resultant velocity of the plane be? 12. Graphing question on next page HW6B – Castle Learning HW6 Answers – 1) based on max and min values, only 55 is possible, 2) yes, a vector in the y direction has zero x component, 3) Vx=8.68 mi/hr E, Vy=49.24 mi/hr N, 4) 25.5m @ 11.31° W of N (or 78.69° N of W), 5) Kx=386.4 km/h W, Ky=103.5 km/h S, 6a) 7.62 m @ 66.8° S of E, b) 14.32m @ 12.09° W of N, 7a) 42.72 m/s @ 20.56° N of E, b) 2.5 sec, 8) 621.4 km @ 34.36° W of N (or 55.61° N or W) 9) max=24 ft, min=4 ft, 10a) 18.75 km, 49.2 km, b) 66.11 km/hr @ 21.85° E of S. 11a) 261 m/s @ 73.3° N of W, b) 325 m/s north PAGE 1 of 2 12) A drag racer test drives a 100 m race strip with a variety of average velocities over the 100m distance. The time and velocity data is shown below. velocity (m/s) 10 20 30 40 50 60 time (s) 10.00 5.00 3.33 2.50 2.00 1.67 a) Make a graph of velocity vs time and draw a best fit line or curve to fit the data. Label the axis b) What specific type of relationship between velocity and time does this graph show. Answer 12) graph is a half parabola, it is an inverse relationship Physics HW #7 PAGE 1 of 2 HW7A Questions Problems 1-5 (Put your answers on the answer sheet and use extra paper if needed) 1.) A bowling ball with a negative initial velocity slows down as it rolls down the lane toward the pins. Is the bowling ball’s acceleration positive or negative as it rolls toward the pins? Explain your answer using the equation a = Δv / t 2.) Two cars are moving in the same direction in parallel lanes along a highway. At some instant, the instantaneous velocity of car A exceeds the instantaneous velocity of car B. Does this mean that car A’s acceleration is DEFINITELY greater than car B’s? Explain, and specifically give an example of how it does or does not show this. 3.) What would be the acceleration of a turtle that is moving with a constant velocity of 0.25 m/s to the right?, explain. 4.) A car is moving along the roadway with oil dripping from the bottom. For each oil drip pattern shown below, explain specifically how the car would be moving to produce the pattern shown. a) ● ● b) ● ● c) ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 5.) If a car is traveling eastward, can its acceleration be westward? Explain and use an example. 6.) Nathan accelerates his skateboard uniformly along a straight path directed east from rest to 7.5 m/s in 2.5 sec. (a) what is Nathan’s acceleration, (b) what is Nathan’s displacement during this time interval, (c) what is Nathan’s average velocity during this time interval 7.) A ball initially at rest rolls down a hill with an acceleration of 3.3 m/s 2. If it accelerates for 5.5 sec, how far will it move? 8.) A plane lands with a velocity of 120 m/s and accelerates at a maximum rate of – 6 m/s2 (a) from the instant the plane touches the runway, what is the minimum time needed before it can come to rest. (b) Can this plane land on an aircraft carrier with a runway that is 0.80 km long, justify your answer. 9.) A sailboat starts from rest and accelerates at a rate of 0.21 m/s 2 over a distance of 245 m. (a) find the magnitude of the boats final velocity (b) find the time it takes the boat to travel this distance. 10.) A car starting at an unknown initial speed accelerates uniformly over 12 m in 5 seconds at which time it has stopped. What is the initial speed of the car? (need multiple steps). 11.) Graphing question on next page HW7B – Castle Learning HW7A Answers - 1) –v needs +a to slow, 2) no, accel is changing velocity and not related to inst. velocity. 3) zero, 4a) speed up, b)constant, c) slowing then constant, 5) yes, move east and slow down, 6a) 3 m/s 2 east, b) 9.38 m east, c) 3.75 m/s east, 7) 49.91 m, 8a) 20 sec, b) 1200 m needed so NO, 9a) 10.14 m/s, b) 48.29 sec, 10) 4.8 m/s PAGE 2 of 2 11) Using the information in the data table, construct a graph on the grid a) Plot the data points. b) Draw the line of best-fit. c) On the same grid, sketch a line representing an object decelerating uniformly in a straight line. d) find the slope of the best fit line e) the slope of this line, ∆y / ∆x, represents what physical quantity. Answer 11) linear best fit line, connect 0,0. Using only pts ON the line, find slope ~ 1.2 m/s/s, slope ∆y/x is ∆v/t so is accel. Physics HW #8 PAGE 1 of 1 HW8A Questions 1. A car starts from rest and travels for 5 sec with a uniform acceleration of +1.1 m/s2. The driver then applies the brakes causing a uniform acceleration of -0.5 m/s2. If the brakes are applied for 3 sec (a) how fast is the car going at the end of the braking period, and (b) how far has it gone from its start. 2. A ball is rolling forward with an unknown initial velocity and rolls for 4 seconds over 12 m. The ball accelerates at a rate of 0.6 m/s2. Find (a) the average velocity of the ball, (b) the initial velocity of the ball and (c) the final velocity of the ball. 3. A car travels east at an average speed of 10 m/s for 200 m and then continues east for 350 m at an average speed of 4 m/s. Determine the average velocity of the car over the whole trip. 4. Force A with a magnitude of 5.6 newtons and force B with a magnitude of 9.4 newtons act concurrently on point P. a) Determine the scale used in the diagram. b) On the diagram, use a ruler and protractor to construct a vector representing the resultant of forces A and B. c) Determine the magnitude of the resultant force. HW8B – Castle Learning HW8A Answers – 1a) 4 m/s, b) 28m, 2a) 3 m/s forward, b) 1.8 m/s forward, c) 4.2 m/s forward, 3) 5.12 m/s east, 4a) 1cm = 2N, b) redraw head to tail to get a resultant pointing up and left, c) 7.4 N Physics HW #9 & 10 Questions 1-2 1) During which interval is the cart moving forward at constant speed? 2) During which interval is the cart increasing speed Questions 3-6 3) What is the carts velocity at 6 seconds 4) When is the cart stopped 5) What is the displacement of the vehicle at 5 seconds 6) How far did the cart travel over the entire trip PAGE 1 of 2 Questions 9-11 PAGE 2 of 2 7) At what times is the car stopped? 8) Determine the carts acceleration at 7 seconds. 9) How far did the car travel from 0-3 seconds? 10) At what times was the speed constant? 11) How far did the car travel from 5-6 seconds? HW9B-10B – Castle Learning for both Answers - HW9A-10A 1) BC, 2) AB, 3) – 2 m/s, 4) 2-4 sec, 5) +6m, 6) 16 m, 7) 0 sec, 10 sec, 8) – 7.5 m/s2, 9) 25 m, 10) 1-3, 5-6 sec, 11) 25 m Intentional Blank Page Physics HW #11 PAGE 1 of 2 HW11A Questions – Unless otherwise indicated, assume no air resistance in all problems 1.) A coin is tossed vertically upward (no air resistance). (a) Describe what happens to the velocity over the entire course of its path in the air (b) does the acceleration increase, decrease or remain constant while in the air? 2.) A pebble is dropped down a well and hits the water 1.25 sec later. Determine the distance from the top of the well to the water below. 3.) A ball is thrown vertically upward, what are the velocity and acceleration at the peak where it reaches its maximum altitude. 4.) A ball is thrown down with an initial speed of 10 m/s. A second ball is dropped from rest at the same height as the first ball. (a) compare the acceleration of each ball while they are in motion. (b) compare the velocity of each ball as they strike the ground. 5.) A flowerpot falls from a windowsill 17.5 m above the ground. (a) How long does it take and (b) with what velocity does it hit the ground. 6.) A cannon ball is launched directly upwards at an initial speed of 17.5 m/s. (a) What maximum height does it reach and (b) how long is it in the air for over its whole up and down trip. 7.) removed – no question 8.) What does it mean when an object reaches terminal velocity? What is the acceleration of an object that reaches terminal velocity, explain. 9.) A ball is thrown upwards and returns to the thrower 3.5 seconds after it was thrown, determine (a) the maximum height of the ball and, (b) the initial throwing speed, (c) the velocity when it returns to the thrower. 10) A student throws a baseball vertically upward and then catches it. If vertically upward is considered to be the positive direction, which graph best represents the relationship between velocity and time for the baseball? [Neglect friction.] 11) Graph, next page. HW11B – Castle Learning HW11A – Answers 1a) dec, 0, then inc., b) a is const at -9.81, 2) 7.66 m, 3) v=0, a= – 9.81m/s2, 4) same, thrown one hits faster (duh) 5a) 1.89 sec, b) –18.54 m/s, 6a) 15.63 m, b) 3.57 sec, 8) doesn’t get any faster, reaches final falling speed and has accel=0, 9a) 15.02 m, b) 17.17 m/s, c) –17.17 m/s, 10) choice 4 PAGE 2 of 2 11) A 1.00-kilogram mass was dropped from rest from a height of 25.0 meters above Earth’s surface. The speed of the mass was determined at 5.0-meter intervals and recorded in the data table below. Using the information in the data table, construct a graph on the grid, following the directions below. - Mark an appropriate scale on the axis labeled “Height Above Earth’s Surface (m).” - Plot the data points for speed versus height above Earth’s surface. - Draw the line or curve of best fit. - Using your graph, determine the speed of the mass after it has fallen a vertical distance of 12.5 meters. ANSWER best fit is a curve , speed is read from the graph ~ 16 m/s Physics HW #12 - ignore air resistance unless otherwise indicated. PAGE 1 of 2 HW12A Questions 1. A bullet is fired horizontally and another bullet is dropped simultaneously from the same height. If air resistance is neglected, which bullet hits first, explain your answer. 2. Does a ball dropped out of a window of a moving car take longer to reach the ground than one dropped at the same height from a car at rest, explain. 3. A man is holding two rocks at equal heights. One is dropped and the other is thrown horizontally. (a) which rock hits first (b) which rock will have a greater velocity when it hits 4. A certain gun type fires bullets at 60 m/s regardless of its orientation. One Bullet is fired with the gun aimed at 10° above the horizontal, a second bullet is fired simultaneously at 45° above the horizontal and a third bullet is fired simultaneously at an angle of 60°. Ignoring air resistance, answer the questions that follow and explain your choice for each one. (a) which hits the ground first, (b) which goes the highest, (c) which has the greatest range, (d) which has the largest x component (e) which has the greatest acceleration 5. (A) On the diagram; construct the x and y components of the velocity at point A. Draw them to scale in relation to the given vector already at point A B A (B) Given that the scale used in the drawing is 1 cm = 2 m/s, use a ruler and the given scale to determine values for the initial velocity as well as initial x and y components. Label them on the diagram. (C) Use a ruler and the rules of projectiles to sketch the velocity vector, as well as the x and y components of the velocity at position B shown in the diagram. Draw it to scale and label the value of each quantity on the diagram. 6. A plane traveling at and altitude of 45 m is moving with a speed of 95 m/s. A package is dropped out of the plane traveling with the same horizontal velocity as the plane. What horizontal distance does the package travel before hitting the ground? 7. A car drives horizontally off a 10 m high bridge and lands in the water below 20 m away horizontally from the base of the bridge. How fast was the car traveling when it left the bridge? 8. A ball is thrown at an angle of 20° above the horizontal relative to the ground at a speed of 23 m/s. If the ball was caught 34.58 m away from the thrower,(a) how long was it in the air for and (b) how high did it go. 9. A soccer ball on the ground is kicked at 8 m/s @ 40 degrees above horizontal and hits the ground at some time later on (a) how long is the ball in the air for, (b) what is the range of the balls motion, (c) what is the max height 10) removed – no question 11,12,13) – continued on next page HW12B – Castle Learning PAGE 2 of 2 11) A machine fired several projectiles at the same angle, θ, above the horizontal. Each projectile was fired with a different initial velocity, vi. The graph below represents the relationship between the magnitude of the initial vertical velocity, viy, and the magnitude of the corresponding initial velocity, vi, of these projectiles. a) Determine the magnitude of the initial vertical velocity of the projectile, viy, when the magnitude of its initial velocity, vi, was 40 meters per second. b) Determine the angle, θ, above the horizontal at which the projectiles were fired. c) Calculate the magnitude of the initial horizontal velocity of the projectile, vix, when the magnitude of its initial velocity, vi, was 40. meters per second. 12) A projectile is fired from the ground with an initial velocity of 250 meters per second at an angle of 60.° above the horizontal a) Use a protractor and ruler to draw a vector to represent the initial velocity of the projectile. Use a scale of 1.0 centimeter = 50. meters per second. b) Determine the horizontal component of the initial velocity. c) Explain why the projectile has no acceleration in the horizontal direction. 13) A kicked soccer ball has an initial velocity of 25 meters per second at an angle of 40° above the horizontal, level ground. Sketch the path of the ball’s flight from its initial position at point P until it returns to level ground. HW12A Answers - 1,2 – same question, both hit at same time (independence of motion), 3a) same time b) since velocity is a combination of x-y the thrown one will hit with an larger velocity due to both x&y components together, 4a) lowest angle hits first, least time, b) big angle most time / most height, c) 45° gives max range, d) lowest angle most x comp, e) all same accel (-9.81), 5) drawing components and measuring each gives V a= 4.4 m/s, Vax= 2.4 m/s ,Vay= 3.4 m/s , Vb= 2.6 m/s, Vbx= 2.4 m/s , Vby= 0.8 m/s, 6) 287.85 m, 7) 14 m/s, 8a) 1.6 sec, 3.16 m, 9a) 1.05 sec, b) 6.42 m , c) 1.35 m, 11a) 25 m/s, b) 39°, c) 31 m/s, 12a) draw to scale, b) 125 m/s, c) no gravity or other forces in x direction, 13) parabolic curve Physics HW #14 PAGE 1 of 2 1 – How does the inertia of a 2 kilogram rock compare to the inertia of a 1 kilogram rock? (explain) 2 – If you were in a spaceship and fired a cannonball into frictionless space, how much force would have to be exerted on the ball to keep it going, explain. 3 – Which has more inertia, a bullet traveling at 100 m/s or a bowling ball slowly rolling across the floor, explain. 4 – If an elephant were chasing you, its enormous mass would be very threatening. But if you zigzagged, the elephant’s mass would be to your advantage. Why? 5 – What is the net force or, equivalently, the resultant force acting on an object in equilibrium? 6 – Forces of 10 N and 15 N in the same direction act on an object. What is the net force on the object? 7 – Suppose a cart is being moved by a certain net force. If the net force is doubled, by how much does the cart’s acceleration change? (explain or show example) 8 – Suppose a cart is being moved by a certain net force. If a load is dumped into the cart so its mass is doubled, by how much does the acceleration change? (explain or show example) 9 – How much net force acts on a 20,000 kg rocket that accelerates at 1 m/s2 10 – If an object has no acceleration, can you conclude that no forces are exerted on it? Explain. 11 – A rocket fired from its launching pad not only picks up speed, but its acceleration also increases significantly as firing continues, why is this so? (Hint: about 90% of the mass of a newly launched rocket is fuel.) PAGE 2 of 2 12 – A horizontal force of 100 N is required to push a crate across a factory floor at a constant speed. What is the net force acting on the crate? What is the force of friction acting on the crate, justify your answers. 13 – The force of gravity is twice as great on a 2kg rock as on a 1 kg rock. Why does the 2 kg rock not fall with twice the acceleration? 14 – Why do a coin and a feather in a vacuum tube fall with the same acceleration? 15 – When a hammer exerts a force on a nail, how does the amount of force compare with that of the nail on the hammer? 16 – When swimming, you push the water backward – call this action. What is the reaction force? 17 – When a rifle is fired, how does the size of the force of the rifle on the bullet compare with the force of the bullet on the rifle? How does the acceleration of the rifle compare with that of the bullet? Defend your answer. 18 – How can a rocket travel in space where there is no air to “push against”? 19 – If you hit a wall with a force of 200 N, how much force is exerted on you? 20 – A speeding bus makes contact with a bug that splatters onto the windshield. Because of the sudden force, the unfortunate bug undergoes a sudden deceleration. Is the corresponding force that the bug exerts against the windshield greater, less, or the same? Is the resulting deceleration of the bus greater than, less than, or the same as that of the bug? Explain. Physics HW #15 PAGE 1 of 1 1 – What is the effect of friction on a moving object? 2 – What is the cause of friction, and in what direction does it act with respect to the motion of a sliding object? 3 – If the force of friction acting on a sliding crate is 100 N, how much force must be applied to maintain a constant velocity? What will be the net force acting on the crate? What will be the acceleration? 4 – Static friction said to be a variable force while kinetic friction is not. Give an example of this and explain fully. 5 – A man pushes horizontally on a box that rests on a horizontal rough surface. Why is it harder to start moving the box then it is to keep it moving? 6 – What is the weight of 2 kilograms of yogurt? 7 – Susie finds she weighs 300 N. Calculate her mass. 8 – When a junked car is crushed into a compact cube, does its mass change? Its volume? Its weight? 9 – A moon rock has a mass of 10 kg on the moon. What is its mass on the earth? 10 – An object weighs 500 N on the moon. What is its mass? Intentional Blank Page Physics HW #16 PAGE 1 of 2 1.) (a) Draw a free body diagram of a football while it is being drop kicked and the foot is in contact with the ball. Since it is drop kicked, the ball is not in contact with the ground. (b) Draw the free body diagram of the ball while it is moving in the friction free air after it has left the players foot. 2).. removed 3.) Identify the action-reaction pairs in the following situations: ACTION FORCE REACTION FORCE (a) a person takes a step (b) a snowball hits someone in the back (c) a baseball player catches a ball in a glove (d) a gust a wind (air) strikes a window 4.) Draw a free body diagram for each of the following situations (a) a projectile at the top of its trajectory in motion in the presence of air resistance (b) a rocket leaving the launch pad with its engines operating (c) a heavy crate being pushed up a rough incline. 5.) A bag of sugar has a mass of 2.26 kg. (a) What is its weight on the moon (b) The acceleration of gravity on Jupiter is 2.64 times that on earth. How much would the bag weigh there. PAGE 2 of 2 6.) Is it possible for an object to be moving if no net force is acting on it? Explain. 7.) If an object is at rest can we conclude that no external forces are acting on it, explain. 8.) An object thrown into the air momentarily stops at the highest point in its path. Is it in equilibrium at this point, explain. 9.) What physical quantity is a measure of the amount of inertia an object has? 10-11.) … removed Physics HW #18 PAGE 1 of 2 RETURN OF CASTLE LEARNING – Castle Learning assignments will return and they will begin to have review problems on them as well from prior topics HW 18A – Problems Below These are not the easiest problems in the world. Be careful about how you draw the FBD diagrams, read the details carefully. Give them a shot and see if you can do them, struggle with them a little, that’s how you learn. Hints are posted on the website with diagrams to make sure your FBDs are correct. If you have tried to figure these out and are stuck, just go and look at the hints … they are infinitely helpful. http:/wells.xroad.com 1) A 3.2 kg bucket of water is raised from a well by a rope. If the upward acceleration of the bucket is 1.75 m/s2, find the force exerted by the rope on the bucket 2) A woman pushes on a 20 kg lawnmower with a force of 23.5 N directed at 30° below the horizontal and towards the right. The mower moves to the right and a 4.2 N friction force opposes the motion of the mower. (a) Determine the acceleration of the mower (b) Determine the normal force acting on the mower 3) You, with your infinite power can exert a maximum force of 100 N on any object. You use your maximum force on an object and push it horizontally on a surface that will exert 25 N of friction force and cause the block to accelerate at 2 m/s2. Are you a wimp?, justify your answer (You will be considered a wimp if you can push less than 50 kg of mass around, so you therefore need to find the mass of the object you push and compare it.) 4) A 100 N box is pulled with 2 forces. A 23 N force directed to the right and a 9 N force directed at 60° up from the horizontal and towards the left. The box moves to the right at a constant speed and a friction force acts to retard (slow) the motion. a.) Determine the friction force acts on the box. b.) Determine the normal force acts on the box. 5) In the scaled diagram, two forces, F1 and F2, act on a 4.0-kilogram block at point P. Force F1 has a magnitude of 12.0 newtons, and is directed toward the right. a) Using a ruler and the scaled diagram, determine the magnitude of F2 in newtons b) Determine the magnitude of the net force acting on the block. c) Calculate the magnitude of the acceleration of the block. 6) Graph question on next page Answers: 1) 37 N, 2a) 0.81 m/s2, b) 208 N, 3) Since you can only push 37.5 kg, you are a wimp, 4a) 18.5 N, b) 92.2 N, 5a) measuring F1 we find scale 1cm = 2.31 N, then measuring F2 we get 9 N 5b) 3N, c) 0.75 m/s2 HW18B – Castle Learning, login and complete assignment PAGE 2 of 2 6) A constant force is applied to a variety of masses and the acceleration of each mass is measured as shown in the table below. Mass (kg) Acceleration (m/s2) 10 5.00 15 3.33 20 2.50 25 2.00 30 1.67 35 1.43 40 1.25 Create a graph of acceleration vs mass for the provided data, properly labeling the graph and axis. What specific type of mathematical relationship does this graph indicate? Does this relationship make sense in relation to Newton second law? Physics HW #19 PAGE 1 of 1 HW19 A - Problems 1) A 10 kilogram rubber block is pulled horizontally with a horizontally applied force and it moves at a constant velocity of 2 m/s across a sheet of ice. a) Calculate the magnitude of the force of friction acting on the block. b) Calculate the pushing force 2) A 25 kg chair initially at rest on a horizontal floor requires a 380 N horizontal force to set it in motion. Once the chair is in motion, a 340 N horizontal force keeps it moving at a constant velocity. (a) find the coefficient of static friction between the chair and the floor (b) find the coefficient of kinetic friction between the chair and the floor. 3) A student moves a box of books down the hall by pulling on a rope attached to a wood box. The student pulls with a force of 170 N at an angle of 20° above the horizontal. The WOOD box has a mass of 28 kg and it is pulled across a WOOD floor. Find the acceleration of the box. 4) A 2.75 kg block is pushed along the ceiling with a constant applied force of 85 N that acts at and angle of 55° with the horizontal as shown in the figure. The block accelerates to the right at 6 m/s2. Determine the coefficient of kinetic friction between the block and the ceiling. The FBD is tricky for this problem, remember that the normal force always comes outward from the surface. Refer to website for further help. 5) A box of books weighing 319 N is on a surface with a coefficient of kinetic friction between the box and the floor of 0.57 and a coefficient of static friction of 0.62 (a) A horizontal force is applied to the box. What is the minimum amount of force needed to set the box into motion. 6) … removed 7) A 10 kg box is pushed across a surface at a constant speed oriented as shown, and 49 N of pushing force is used. A) Determine the coefficient of kinetic friction between the box and surface. B) The box is turned on its side so that half of the area of the box is touching the table, but still only 49N of force is needed to slide it at a constant speed, determine the coefficient of friction. C) What does this imply about the effect of surface area on the coefficient of friction? A B Answers – 1a) 14.7 N b) since Fnet=0, Fpush=Fk, so also 14.7 N 2a) 1.55, b) 1.39, 3) a=3.38 m/s2 (note: Fn=216.54, fk=65), 4) u=0.76 (note: Fn=42.53, fk=32.25) 5a) 197.8 N, 7) u = 0.5 for both answers, fk and Fn are the same in each. Surface area does not affect u, only surface type does. HW19B – Castle Learning – log in and complete the assignment Intentional Blank Page Physics HW #20 PAGE 1 of 2 HW20A – Problems Below 1.) A 72 kg box slides down a 22° ramp. The coefficient of kinetic friction between the box and the ramp is 0.17. Determine the acceleration of the box as it slides down the ramp. 2.) A girl on a sled starts from rest and coasts down a 50 degree inclined hill in 2.5 seconds, reaching level ground at the bottom with a speed of 3.25 m/s. The girl and sled together weigh 645 N. (a) Determine the acceleration on the incline, (b) Determine the coefficient of kinetic friction on this incline 3.) A 981 N kid slides in dirt with a coefficient of kinetic friction of 0.5 moving at an initial speed of 3.25 m/s and travels an unknown distance until she comes to rest. Determine the distance the girl travels on the flat ground before coming to rest. 4.) A 2.8 kg steel block on a 26° steel incline and is pushed up the incline at a constant speed with a force parallel to the length of the incline. Find the force pushing the block up the incline 5.) Graphing Question on next page HW20B – Castle Learning - Logon to castle learning and complete the multiple choice questions Answers – 1) a=2.13 m/s2 (fk=111.33, Fn=654.9), 2) use kinematics, a=1.3m/s2, u=0.985 (fk=408.5, Fn=414.6) 3) d = 1/08 m (a=4.91 m/s2), 4) Look up u on ref table. F=26.11 N (const speed is key, fk=14.07, Fn=24.7) PAGE 2 of 2 5.) A box is placed on an incline and remains at rest as the angle is slowly increased. The friction force and max static friction force is determined for each angle increase. a) In the table, how is the “friction force” calculated, show a sample calculation for the first value in the table (draw a FBD and use it to think about how the actual static friction force acting is found b) On the graph below, plot both “friction force vs θ” and “fs(max) vs. θ” (two separate trend lines on the same graph). Use some sort of legend to distinguish each line. Be sure to leave some extra graph grid spaces to the right (meaning don’t use the whole graph for your plot and leave some blank space left over), label the axis appropriately. Friction vs. Angle c) Based on the graph above, estimate the angle at which the box would slip, explain how you did it d) Using any of the values from the table, determine the value of µs, show work. Physics HW #21, (No castle learning this time) PAGE 1 of 1 This page may be turned instead of loose leaf. 1.) Identify the force that maintains the circular motion of the following (meaning identify which force is the centripetal force) (a) A car rounding a curve on pavement _________________________________ (b) A yo-yo swung in a horizontal circle around someone’s head _________________________________ (c) A boy sliding down a curved slide at a water park _________________________________ 2.) An object moves in a circular path with constant speed, v. (a) Is the objects velocity constant, explain. (b) is the objects acceleration constant, explain. 3.) Give an example of a situation in which an automobile driver can have a centripetal acceleration but not tangential acceleration, explain. 4.) Can a car move around a circular track so that the car has a tangential acceleration but no centripetal acceleration, explain 5.) The gas pedal and the brakes of the car can cause acceleration and deceleration. Explain how a steering wheel can cause acceleration. Intentional Blank Page Physics HW #22 PAGE 1 of 2 HW22A Questions 1.) When a rollercoaster goes around a loop, what force provides the centripetal force at the top of the loop? 2.) Two coins are placed on a record and the record spins. The outside coin is twice as far from the center of the record compared to the other coin, is 3 times as heavy as the inside coin and moves twice as fast as the inside coin. Numerically compare the centripetal force on the outside coin to the inside coin. 3.) A young boy swings a yo-yo horizontally above his head so that the yo-yo has a centripetal acceleration of 40 m/s2. If the yoyo’s string is 0.5 m long, what is the yo-yo’s tangential speed. 4.) A 900 kg test car travels around a circular track that has a length of 3.05 km (the circumference of the track). If the magnitude of the force that maintains the car’s circular motion is 2140 N, what is the car’s tangential speed. 5.) A building superintendent twirls a set of 200 g keys in a horizontal circle at the end of a cord. If the keys have a centripetal acceleration of 125 m/s2 and the tangential speed of the keys is 6.25 m/s, (a) how long is the cord and (b) how much force must the man pull on the attached cord to keep the keys in motion? 6.) A 12000 N car traveling at 45 km/hr rounds a curve of radius 180 m. Find the following (a) the centripetal acceleration of the car (b) the force that maintains the centripetal acceleration (c) the minimum coefficient of static friction between the tires and the road that will allow the car to round the curve safely. 7.) The moon circles the earth once in 28 days at a radial distance as shown on the Regents reference table. (a) Determine the average speed of the moon in its orbit in (m/s). (b) Determine the centripetal force acting on the moon (c) What force provides the centripetal force found in part b 8.) A 1000 kg car travels at constant speed around a section of horizontal, circular track. A) On the diagram, draw an arrow at point P to represent the direction of the centripetal acceleration of the car when it is at point P. B) The radius of the track is 20 m. a) If the car took 15 seconds to travel from start to end, determine the magnitude of the centripetal force at point P. b) What specific type of force provides the centripetal force for the car. 9.) On next page HW22B – castle learning online review problems Answers – 1) Fn, 2) 6x as much, 3) 4.47 m/s, 4) 34 m/s, 5a) 0.3125 m, b) 25 N, 6a) 0.87, b) 1062 N, c) .09 7a) 997.3 m/s, b) 1.9x1020 N, c) gravity, 8a) 878.8 N, b) static friction Question 9) PAGE 2 of 2 In an experiment, a rubber stopper is attached to one end of a string that is passed through a plastic tube before weights are attached to the other end. The stopper is whirled in a horizontal circular path at constant speed. (a) On the diagram of the top view draw the path of the rubber stopper if the string breaks at the position shown. (b) Describe what would happen to the radius of the circle if the student whirls the stopper at a greater speed without changing the balancing weights. (c) List three measurements (easily measureable quantities) that must be taken to show that the magnitude of the centripetal force is equal to the balancing weights. [Neglect friction] (d) The rubber stopper is now whirled in a vertical circle at the same speed. On the diagram draw and label vectors to indicate the direction of the weight (Fg) and the direction of the centripetal force (Fc) at the position shown. Physics HW #23 PAGE 1 of 1 HW23A Questions 1.) Astronauts floating around inside the space shuttle are not actually in a zero-gravity environment. What is the real reason astronauts seem weightless, explain fully. 2.) Describe how satellites are made to orbit and be sure to identify the force that provides the centripetal force to maintain the motion. 3.) Two objects are a distance d apart and experience a gravitational force F. How much would the distance need to change by in order to produce a gravitational force 9 times larger than it initially was? 4.) Two objects are a distance d apart and experience a gravitational force of 2000 N. If the mass of one of the objects was made 4 times larger and the distance between the objects was made 3 times smaller what would the new force be? 5.) Two equal masses are a distance d apart and experience a gravitational force F. The two masses are replaced with different size masses (but still equal to each other). The distance between the two objects is also reduced to ¼ d and the resulting Force is now changed to 64 times the original value. By what factor were the masses changed by compared to their original value? 6.) A 90 kg person stands 2 m away from a 60 kg person sitting on a bench nearby. What is the magnitude of the gravitational force between them? 7.) Mars has a mass of about 6.4 x 1023 kg and its moon Phobos has a mass of about 9.6 x 1015 kg. If the magnitude of the gravitation force between the two bodies is 4.6 x 1015 N, how far apart are Mars and Phoebos 8.) A person stands at the equator of the earth, and is therefore 1 earth radii from the center. The earth rotates one time around in one day. Determine the speed of the person as seen from outer space, assume the earth is a perfect circle. 9.) The period of the moons revolution is 28 days. Determine the speed of the moon around the earth assuming its orbit is circular. 10.) (a) Identify the specific force that provides the centripetal force to keep the Earth revolving around the sun (b) The earth takes 1 year to orbit the sun, assume the orbit is a perfect circle and determine the speed of the earth in its orbit (c) Calculate the force that maintains the circular motion of the earth around the sun. 11.) A 1000 kg satellite is in a geosynchronous orbit around an unknown planet that has the same rotation rate as the earth but is a different size and mass. The satellite is 35000 km above the center of the planet. (a) How fast must the satellite be moving to be in this geosynchronous orbit. (b) Calculate the centripetal force acting on the satellite. (c) Using your answer from b (and knowing the specific force that this centripetal force represents), determine the mass of the planet. HW23B – Castle Learning online problems Answers – 1) free falling, 2) FG = Fnet(c), 3) 1/3 x, 4) F increase by 36x, so new F =72000 N, 5) since m2=4 when subbing in numbers, each mass must have been doubled, 6) 9x10-8 N, 7) 9.44x106 N, 8) 463.24 m/s, 9) 997.33 m/s, 10) gravity, 29886 m/s, 3.56x10 22 N, 11) 2545.27 m/s, 185.1 N, 3.4x1024 kg Physics HW #24 Page 1 of 1 HW 24A - Questions 1.) For each example below, indicate whether the work done on the second object will have a positive, negative or zero value. (a) The road exerts a friction force on a speeding car skidding to a stop (b) A rope exerts a force on a bucket as the bucket is raised up a well (c) Air exerts a force on a parachute as the parachutist slowly falls to Earth (d) A man pushes on a stationary wall. 2.) If 2.15 J of work is done by a person lifting a 160 g apple at a constant speed, how far is it lifted 3.) A worker pushes a 1.25x103 N crate horizontally with a force of 500 N @ 30 degrees below the horizontal, and he moves it a distance of 24 m. The coefficient of kinetic friction between the crate and the floor is 0.10 (a) How much work is done by the worker on the crate (b) How much work is done by friction on the crate (c) How much work is done by gravity (d) What is the net work done on the crate 4.) A car with a mass of 2.5x103 kg starts from rest and accelerates to a speed of 16.5 m/s in 11.5 sec as it is pushed horizontally by the force of the car’s engine. Assume that the force of resistance (friction, air resistance) against the motion of the car remains constant at 400 N during this time. (a) What is the acceleration of the car (b) What is the force of the engine (c) What is the average power of the car engine. 5.) A harrier jet plane is designed for vertical takeoff and has a mass of 8x10 3 kg. Find the net work done on the plane as it accelerates upward at 0.9 m/s2 through a distance of 30 m after starting from rest. 6.) A car at rest has a 144 kW engine operate for 1.8 minutes to bring it to a final speed of 5 m/s. (a) How much force did the engine exert on the car. (b) How much work was done on the car. 7.) A constant force of 20 N acts on a box. The box is moving at a constant speed of 3.7 m/s. (a) How much work is done by the force in 6 seconds? (b) How much net work is done? 8.) A 10.-kilogram block is pushed across a floor by a horizontal force of 50. newtons. The block moves from point A to point B in 3.0 seconds. a) Using a scale of 1.0 centimeter = 2 meters, determine the magnitude of the displacement of the block as it moves from point A to point B b) Calculate the power required to move the block from point A to point B in 3.0 seconds. HW24 B – Castle Learning Problems Answers – 1) -, +, -, 0 2) 1.37 m, 3) + 10392.3 J, -3600 J, 0, 6792.3 J, 4) 1.435 m/s2, 3975 N, 32800 W, 5) 216000 J, 6) 57600 N, 1.56x107 J, 7) 444 J, 0, 8) measure 16.3 m, 271.67 W Physics HW #25 Page 1 of 2 HW25A Questions 1.) A car has a kinetic energy of 4.32x105 J when traveling at a speed of 18 m/s. (a) What is its mass? (b) How fast would a 10 kg bowling ball have to travel to have the same energy as the car. 2.) A pinball bangs against a bumper giving the ball a speed of 26 cm/s. If the ball has a mass of 40 g, what is the balls kinetic energy in joules. 3.) A spoon is raised 15 cm above a table. If the spoon and its contents have a mass of 28 g, what is the gravitational potential energy associated with the spoon at that height relative to the table surface. 4.) A 75 kg skydiver is 850 m above the earth’s surface moving at 36 m/s. What is the mechanical energy of the skydiver at this point (express your answer in scientific notation). 5.) A spring lying horizontally at rest has a length of 1m. A 9.5 N force holds the spring at a new length of 1.20 m. What is the elastic energy in the spring? 6.) A spring with a spring constant of 100 N/m is attached to the ceiling and a 5 kg mass is attached to it. The stretched length of the spring is measured to be 1.75 m. What is the relaxed length of the spring. 7.) A 25 cm long spring with a force constant of 1.7 N/m is sitting on the ground in a vertical position. A mass is placed on top of the spring and it compresses it 10 cm. (a) Find the Force in the spring, (b) Find the value of the mass placed on the spring , (c) find the elastic energy in the spring 8.) A 10 cm long spring with a spring constant of 45 N/m rests horizontally and is stretched to a new length of 60 cm. Calculate the elastic potential energy in the spring 9.) The graph below, represents the relationship between vertical height and gravitational potential energy for an object near Earth’s surface. (The same graph appears in your answer booklet.) a) Based on the graph, what is the gravitational potential energy of the object when it is 2.25 meters above the surface of Earth? b) Using the graph, calculate the mass of the object. c) What physical quantity does the slope of the graph represent? d) Using a straightedge, draw a line on the graph in your answer booklet to represent the relationship between gravitational potential energy and vertical height for an object having a greater mass. Page 2 of 2 10.) A student performed an experiment in which the weight attached to a suspended spring was varied and the resulting total length of the spring measured. The data for the experiment are in the table below. a) Using the information in the data table, construct a graph, following the directions below. - Plot the data points for the attached weight versus total spring length. - Label and title your graph appropriately with units. - Draw the line or curve of best fit. b) Using your graph, determine the length of the spring before any weight was attached. c) Using your graph, determine the spring constant of the spring HW25B – Castle Learning ANSWERS – 1a) 2666.7 kg, b) 293.94 m/s, 2) 0.00135 J, 3) 0.0412 J, 4) 674000 J, 5) 0.95 J, m, 6) 1.26 m, 7a) 0.17 N, b) 0.017 kg, c) 0.0085 J, 8) 5.625 J, 9) 55J, 2.49 kg, weight, linear but slightly more slope, 10) be sure it’s a best fit linear line, relaxed length: extend line to x axis = 0.29 m, k = slope = 13.69 N/m Physics HW #26 Page 1 of 2 HW26A Questions – A 1.) A 100 gram marble rolls on the frictionless track shown starting from a height of h = 26 cm as shown below. The ball is released from rest at A. Calculate (a) the speed at B (c) the speed at point C C h 2/3 h B 2.) A 40 kg pole vaulter runs on the ground at 10 m/s and vaults over a bar of unknown height. The velocity when the runner goes over the bar is 2 m/s. Ignoring air resistance, how high is the bar? 3.) A 2600 N box slides across a table with a coefficient of kinetic friction of 0.25 and it comes to rest after traveling 26 m. (a) How much work is done by friction (b) What is the change in energy of the box as it slides across the surface. (c) What is the initial speed of the box 4.) A horizontal spring with a force constant (spring constant) of 80 N/m is compressed on a frictionless surface, a distance of 9.5 cm from its relaxed length. A 36 g box is placed next to it and is released. What will the speed of the box be when the spring reaches its relaxed length and the box leaves the spring? 5.) A horizontal BB gun, 2.25 m off the ground, fires a pebble of mass m at a horizontal velocity of 5 m/s. (a) Use energy conservation to determine the speed of the BB when it hits the ground (b) Use projectile methods to determine how far away the ball landed from the shooter. VF=0 2600 N \/\/\/\/\ /\/\/\/\/\/\/\/\/\/\/\/ \ dY dX 6.) A 9.5 g bullet moving at 360 m/s penetrates a tree trunk to a depth of 36 cm until friction from the tree has stopped it. Use work energy considerations to find the magnitude of the force that stops the bullet 7.) A 1.5 kg box sliding on a frictionless surface at 3 m/s hits a 50 cm long horizontal spring and compresses it by 10 cm until it comes to rest. (a) Determine the spring constant of the spring. (b) How much work is done by the spring to stop the box /\/\/\/\/\/\/\/\/\/\/\/ /\/\/\/\/\ \ 8.) An average force of 50 N is needed to compress a spring 5 cm. How much elastic energy is stored in the spring. 9.) A spring was compressed 5 cm by a variable force and held in place by a 50 N force, how much elastic energy would be stored in the spring. 10.) A box at the top of a rough incline possesses 981 joules of gravitational potential energy compared to the bottom of the incline. As the box slides to the bottom of the incline, 245 joules of heat is produced. Determine the kinetic energy of the box at the bottom of the incline. 11.) A 10 kg box moving with a kinetic energy of 500 J slides across a rough patch. It moves across the patch and emerges at a speed of 8 m/s. (a) How much internal energy is generated as the box moves across the patch (b) If the coefficient of kinetic friction was 0.4, how long was the rough patch? 12.) A spring with a spring constant of 40 newtons per meter is compressed by a force of 30 newtons. What is the total elastic potential energy stored in this compressed spring? Page 2 of 2 13.) Using the graph, determine the total work done in moving the box 6.0 meters? 14.) The graph below represents the motion of a 5 gram marble moving on a rollercoaster track. Note that the scale on the y axis has units x 10-4 (therefore the “20” on the y axis is actually 20 x 10-4 J). a) From the graph, by how much does the mechanical energy change over the course of the trip b) What is most likely the cause of this loss of mechanical energy, and where does the energy go c) What is the speed of the marble at 0.4 sec? (this about which energy you can use to get speed) d) What is the maximum height of the marble? (think about which energy you can use to get height and where on the graph the largest amount is) Kinetic Time vs. Energy Potential Total 180 x10-4 180 160 x10-4 160 Energy (J) 140 x10-4 140 120 x10-4 120 100 x10-4 100 80 x10 80-4 60 x10 60-4 40 x10 40-4 20-4 20 x10 0 0 0.5 1 1.5 Time (sec) HW26B – Castle Learning Answers: 1a) 2.26 m/s, b) 1.3 m/s, 2) 4.89 m, 3a) -16900 J, b) -16900 J, c) 11.29 m/s, 4) 4.47 m/s, 5a) 8.32 m/s, b) 3.39 m, 6) 1710 N, 7a) 1350 N/m, b) 6.75 J, 8) 2.5 J, 9) 1.25J, 10) 736 J, 11a) 180J, b) 4.59 m, 12) 11.25 J, 13) 27 J, 14a) 30x10-4 J, b) friction, internal energy, c) 1.67 m/s, d) 0.31 m Physics HW #28 Page 1 of 1 HW28A Questions 1.) The speed of a particle is doubled (a) by what factor is its momentum changed (b) What happens to its kinetic energy 2.) When a force is exerted on an object, does a large force always produce a larger change in the object’s momentum than a smaller force does, explain 3.) What is the relationship between impulse and momentum 4.) A truck loaded with sand is moving down the highway in a straight pate (a) What happens to the momentum of the truck if the truck’s velocity is increasing. (b) What happens to the momentum of the truck if sand leaks at a constant rate through a hole in the truck bed while the truck maintains a constant velocity. Explain answers. 5.) When a car collision occurs, an air bag is inflated, protecting the passenger from serious injury. How does the air bag soften the blow? Use physics terms involved with impulse and momentum to explain. 6.) If you jump from a table onto the floor, are you more likely to be hurt if your legs are relaxed or stiff and your knees are locked? Use physics terms involved with impulse and momentum to explain. 7.) A 0.40 kg soccer ball approaches a player horizontally with a velocity of 10 m/s to the north. The player strikes the ball and causes it to move in the opposite direction with a velocity of 13 m/s. What impulse was delivered to the ball by the player? 8.) A 4.7 kg ball strikes the wall with a velocity of 8.5 m/s to the left. The ball bounces off with a velocity of 7.5 m/s to the right. If the ball is in contact with the wall for 0.10 sec, what is the constant force exerted on the ball by the wall? 9.) A 14 g baseball moving at +22 m/s is slowed to a stop by a catcher who exerts a constant force of 300 N in a direction opposite the motion of the ball. (a) How long does it take this force to stop the ball? (b) How far does the ball sink into the catchers mitt before stopping? 10.) A 51 kg pole-vaulter falls from rest from a height of 4 m onto a foam-rubber pad. After falling the 4 m, the pole vaulter then hits the mat and is in brought to rest while in contact with the mat for 0.3 seconds. (a) Calculate the athlete’s velocity just before reaching the pad (b) Calculate the net force acting on the vaulter while he is being brought to rest by the mat . (Note, there are two parts, the fall and then the part where the man sinks into the pad). 11.) A 1000-kilogram car traveling due east at 15 meters per second is hit from behind and receives a forward impulse of 6000 newton-seconds. Determine the magnitude of the car’s change in momentum due to this impulse. 12.) A car with mass m possesses momentum of magnitude p. Which expression correctly represents the kinetic energy, KE, of the car in terms of m and p? HW28B – Castle Learning (online) Answers: 1) a) x2, b) x4, 2) No, time matters also, J=Δp=Ft, 3) J=Δp, 4) based on p=mv … a) p inc., b) p dec, 5) more t less F, 6) stiff, less t more F, 7) 9.2 Ns South, 8) 752 N right, 9a) 0.001 sec, b)0.0113 m, 10a) 8.86 m/s, b) 1506.2 N, 11) 6000 kg m/s, 12) sub in p=mv and cancel m to get choice 4. Physics HW #29 Page 1 of 1 HW 29A Questions 1.) Two skaters on ice are facing each other touching and initially push against each other so that they move in opposite directions. What is the total momentum of the two skaters when they begin moving? Explain your answer. 2.) An astronaut carrying a camera in space finds herself drifting away from a space shuttle after her tether strap becomes unfastened. If she has no propulsion device, what should she do to move back to the shuttle? 3.) Given the masses of two objects and their velocities before and after a head on collision, how could you determine whether the collision was elastic, inelastic, or perfectly inelastic? Explain and refer to how you would use the velocities given to find the answer. 4.) A person on a 2.1 kg skateboard initially at rest tosses a 6.5 kg jug of water in the forward direction. If the jug has a speed of 4 m/s relative the ground and the person and skateboard move in the opposite direction at 0.60 m/s, find the person’s mass. 5.) A 1.2 kg skateboard is coasting along the pavement at a speed of 4.5 m/s when a 0.80 kg cat drops from a tree vertically onto the skateboard. What is the speed of the skateboard-cat combination. 6.) A 150 g toy car moving to the right at 35 cm/s has a collision with a 200 g toy car moving in the opposite direction at 30 cm/s. After colliding, the 150 g car moves with a velocity of 7.1 cm/s to the left. Find the velocity of the 200 g car after the collision, in cm/s, and determine what type of collision this is (show work and explain answer). 7.) A tennis player places a 52 kg ball machine on a frictionless surface. The machine fires a 57 g tennis ball horizontally with a velocity of 32 m/s towards the north. What is the final velocity of the machine 8.) A 50-kilogram child running at 6.0 meters per second jumps onto a stationary 10.-kilogram sled. The sled is on a level frictionless surface. a) Calculate the speed of the sled with the child after she jumps onto the sled. b) Calculate the kinetic energy of the sled with the child after she jumps onto the sled. c) After a short time, the sled reaches a rough level surface that exerts a constant frictional force of 54 newtons on the sled. How much work must be done by friction to bring the sled with the child to a stop? 9.) A 1200-kilogram car moving at 12 meters per second collides with a 2300-kilogram car that is waiting at rest at a traffic light. After the collision, the cars lock together and slide. Eventually, the combined cars are brought to rest by a force of kinetic friction as the rubber tires slide across the dry, level, asphalt road surface. a) Calculate the speed of the locked-together cars immediately after the collision. b) Calculate the magnitude of the frictional force that brings the locked-together cars to rest. c) Calculate the distance over which the frictional force acted to bring the locked-together cars to rest. 10.) A 4.0-kilogram cart moving to the right at 3 m/s and a 6.0-kilogram cart moving to the left at 3 m/s on a horizontal frictionless surface collide with each other and they lock together. Determine the magnitude of the total momentum of the twocart system after the collision. 11.) Two masses collide as shown. Before the collision, mass mA is moving to the right with speed v, and mass mB is at rest. Upon collision, the two masses stick together. Which expression represents the speed, v', of the masses after the collision? HW29B – Castle Learning (online) Answers: 1) zero, + and – cancel, 2) throw camera in direction away from ship, 3) method given in notes, 4) 41.23 kg, 5) 2.7 m/s, 6) 1.58 cm/s, KEi=0.0182 J KEf = 0.0029 J … inelastic since not equal, 7) 0.035 m/s, 8) 5 m/s, 750 J, 750 J, 9a) 4.11 m/s, b) 23000 N, c) 1.29 m, 10) -6 kg m/s, 11) choice 4.