2010 Week Five Problems Impulse-Mom-Energy

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Week 5 Problems: Impulse, Momentum, Energy Momentum and Conservation of Momentum 1. Which of the following quantities are units of momentum? (There could be more than one correct choice.) A) N ∙ m B) kg ∙ s/m C) kg ∙ m/s D) N ∙ s E) kg ∙ m 2 /s 2 Answer: C, D Topic: Momentum 2. A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct? (There could be more than one correct choice.) A) The ball had the same momentum just before and just after the bounce. B) The magnitude of the ball's momentum was the same just before and just after the bounce. C) The ball's momentum was conserved during the bounce. D) None of the above statements are correct. Answer: B Topic: Conservation of Momentum 3. The momentum of an isolated system is conserved A) only in inelastic collisions. B) only in elastic collisions. C) in both elastic and inelastic collisions. Answer: C Topic: Conservation of Momentum 4. Two friends are standing on opposite ends of a canoe that is initially at rest with respect to a frictionless lake. The person in the front throws a very massive ball toward the back, and the person in the back catches it. After the ball is caught, the canoe is A) moving backward. B) stationary. C) moving forward. Answer: B Topic: Conservation of Momentum 5. Which of the following quantities are units of impulse? (There could be more than one correct choice.) A) N ∙ m B) kg ∙ s/m C) kg ∙ m/s D) N ∙ s E) kg ∙ m 2 /s 2 Answer: C, D Topic: Impulse

6. Identical forces act for the same length of time on two different objects. The magnitude of the change in momentum of the lighter object is A) smaller than the magnitude of the change in momentum of the larger mass, but not zero. B) larger than the magnitude of the change in momentum of the larger mass. C) exactly equal to the magnitude of the change in momentum of the larger mass. D) zero. E) There is not enough information to answer the question. Answer: C Topic: Impulse 7. A 5-kg ball collides inelastically head-on with a 10-kg ball, which is initially stationary. Which of the following statements is true? (There could be more than one correct choice.) A) The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball. B) The magnitude of the change of velocity the 5-kg ball experiences is less than that of the 10-kg ball. C) The magnitude of the change of velocity the 5-kg ball experiences is equal to that of the 10-kg ball. D) The magnitude of the change of the momentum of the 5-kg ball is equal to the magnitude of the change of momentum of the 10-kg ball. E) Both balls lose all their momentum since the collision is inelastic. Answer: A, D Topic: Inelastic Collisions Elastic Collisions 8. In a game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves away with the same velocity as the cue ball had originally. Both balls have the same mass. This type of collision is A) somewhat inelastic. B) elastic. C) completely inelastic. Answer: B Topic: Elastic Collisions 9. In the figure, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. The collision is A) perfectly elastic. B) partially inelastic. C) completely inelastic. D) characterized by an increase in kinetic energy. E) not possible because momentum is not conserved. Answer: A Topic: Elastic Collisions 10. An egg falls from a bird's nest in a tree and feels no effects due to the air. As it falls, A) only its kinetic energy is conserved. B) only its momentum is conserved. C) both its kinetic energy and its momentum are conserved. D) only its mechanical energy is conserved. E) both its mechanical energy and its momentum are conserved. Answer: D Topic: Energy and Momentum

11. A railroad car collides with and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system A) is the same as before. B) is half as much as before. C) is one third as much as before. D) is one fourth as much as before. E) is one quarter as much as before. Answer: B Topic: Energy and Momentum 12. On a horizontal frictionless air table, a puck runs into an ideal horizontal spring that is fastened to the table. The puck compresses the spring by 15 cm before coming to rest. During the compression process, which quantities are conserved? A) only the momentum of the puck B) only the kinetic energy of the puck C) only the mechanical energy (kinetic plus potential) of the puck D) the momentum and the mechanical energy of the puck E) the momentum and the kinetic energy of the puck Answer: C Topic: Energy and Momentum 13. There must be equal amounts of mass on both sides of the center of mass (or center of gravity) of a system. A) True B) False Answer: B Topic: Center of Mass 14. What is the magnitude of the momentum of a 0.140 kg baseball traveling at 45.0 m/s? Answer: 6.30 kg ∙ m/s Topic: Momentum 15. A 0.14-kg baseball is dropped from rest from a height of 2.0 m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance? A) 0.28 kg ∙ m/s B) 0.88 kg ∙ m/s C) 0.44 kg ∙ m/s D) 0.62 kg ∙ m/s E) 1.4 kg ∙ m/s Answer: B Topic: Momentum 16. Three objects are moving along a straight line as shown in the figure. Taking the positive direction to be to the right, what is the total momentum of this system? A) +106 kg ∙ m/s B) -106 kg ∙ m/s C) +14.0 kg ∙ m/s D) -14.0 kg ∙ m/s E) 0.00 kg ∙ m/s Answer: D Topic: Momentum

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17. A 100-g ball falls from a window that is 12 m above ground level and experiences no significant air resistance as it falls. What is its momentum when it strikes the ground? A) 3.3 kg ∙ m/s B) 4.8 kg ∙ m/s C) 1.8 kg ∙ m/s D) 1.5 kg ∙ m/s E) 2.4 kg ∙ m/s Answer: D Topic: Momentum 18. A 60-kg swimmer suddenly dives horizontally from a 150-kg raft with a speed of 1.5 m/s. The raft is initially at rest. What is the speed of the raft immediately after the diver jumps if the water has negligible effect on the raft? Answer: 0.60 m/s Topic: Conservation of Momentum 19. A 14,000-kg boxcar is coasting at 1.50 m/s along a horizontal track when it suddenly hits and couples with a stationary 10,000-kg boxcar. What is the speed of the cars just after the collision? Answer: 0.875 m/s Topic: Conservation of Momentum 20. In a police ballistics test, 2.00-g bullet traveling at 700 m/s suddenly hits and becomes embedded in a stationary 5.00-kg wood block. What is the speed of the block immediately after the bullet has stopped moving relative to the block? Answer: 0.280 m/s Topic: Conservation of Momentum 21. Two ice skaters suddenly push off against one another starting from a stationary position. The 45-kg skater acquires a speed of 0.375 m/s relative to the ice. What speed does the 60-kg skater acquire relative to the ice? A) 0.50 m/s B) 0.28 m/s C) 0.38 m/s D) 0.75 m/s E) 0.00 m/s Answer: B Topic: Conservation of Momentum 22. : A 1200-kg cannon suddenly fires a 100-kg cannonball at 35 m/s. What is the recoil speed of the cannon? Assume that frictional forces are negligible, and the cannon is fired horizontally. A) 2.9 m/s B) 35 m/s C) 3.5 m/s D) 3.2 m/s Answer: A Topic: Conservation of Momentum

23. In a police ballistics test, a 10.0-g bullet moving at 300 m/s is fired into a 1.00-kg block at rest. The bullet goes through the block almost instantaneously and emerges with 50.0% of its original speed. What is the speed of the block just after the bullet emerges? A) 1.50 m/s B) 2.97 m/s C) 3.00 m/s D) 273 m/s Answer: A Topic: Conservation of Momentum 24. A batter applies an average force of 8000 N to a baseball for 1.1 ms. What is the magnitude of the impulse delivered to the baseball by the bat? Answer: 8.8 N ∙ s Topic: Impulse 25. A batter hits a 0.140-kg baseball that was approaching him at 30 m/s and, as a result, the ball leaves the bat at 40 m/s in the reverse of its original direction. The ball remains in contact with the bat for 2.0 ms. What is the magnitude of the average force exerted by the bat on the ball? Answer: 4900 N Topic: Impulse 26. Jennifer hits a stationary 0.20-kg ball, and it leaves her racket at 40 m/s. Time-lapse photography shows that the ball was in contact with the racket for 40 ms. (a) What average force did the ball exert on the racket? (b) What is the ratio of this force to the weight of the ball? Answer: (a) 0.20 kN (b) 100 Topic: Impulse 27. A 0.140 kg baseball is thrown horizontally with a velocity of 28.9 m/s. It is struck with a constant horizontal force that lasts for 1.85 ms, which results in a velocity of 37.0 m/s in the opposite direction. What was the magnitude of the horizontal force? A) 0.613 kN B) 2.19 kN C) 2.80 kN D) 4.99 kN Answer: D Topic: Impulse 28. A golf ball of mass 0.050 kg is at rest on the tee. Just after being struck, it has a velocity of 102 m/s. If the club and ball were in contact for 0.81 ms, what is the average force exerted on the ball by the club? A) 6.3 kN B) 7.1 kN C) 5.5 kN D) 4.9 kN Answer: A Topic: Impulse 29: A very small 51-g steel ball is released from rest and falls vertically onto a steel plate. The ball strikes the plate and is in contact with it for 0.50 ms. The ball rebounds elastically and returns to its original height. The total time interval for a round trip is 3.00 s. What is the magnitude of the average force exerted on the ball by the plate during contact with the plate?

A) 3000 N B) 1500 N C) 2490 N D) 2000 N E) 3500 N Answer: A Topic: Impulse 30.: A block of mass m = 5.6 kg, moving on a frictionless surface with a velocity of v i = 6.5 m/s to the right, collides with a block of mass M at rest, as shown in the figure. After the collision, the 5.6-kg block recoils with a velocity of v f = 0.70 m/s to the left. If the blocks are in contact for 0.20 s, what is the magnitude of the average force on the 5.6-kg block, while the two blocks are in contact? A) 202 N B) 192 N C) 182 N D) 34 N E) 162 N Answer: A Topic: Impulse Inelastic Collisions 31. A 2200-kg auto moving northward at 12.0 m/s runs into a 3800-kg truck which is also moving northward, but at 5.00 m/s. If the vehicles lock bumpers, how fast are they moving just after the collision? Answer: 7.57 m/s Topic: Inelastic Collisions 32. A 1200-kg car moving at 15.6 m/s suddenly collides with a stationary car of mass 1500 kg. If the two vehicles lock together, what is their combined velocity immediately after the collision? A) 6.9 m/s B) 8.6 m/s C) 12.1 m/s D) 5.5 m/s Answer: A Topic: Inelastic Collisions 33 A 1000-kg whale swims horizontally to the right at a speed of 6.0 m/s. It suddenly collides directly with a stationary seal of mass 200 kg. The seal grabs onto the whale and holds fast. What is the momentum of these two sea creatures just after their collision? You can neglect any drag effects of the water during the collision. A) 0.00 kg ∙ m/s B) 1200 kg ∙ m/s C) 2000 kg ∙ m/s D) 7200 kg ∙ m/s E) 6000 kg ∙ m/s Answer: E Topic: Inelastic Collisions

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34. A block of mass m = 4.4 kg, moving on frictionless surface with a speed v i = 9.2 m/s makes a sudden perfectly elastic collision with a second block of mass M , as shown in the figure. The second block is originally at rest. Just after the collision, the 4.4-kg block recoils with a speed of v f = 2.5 m/s. What is the mass M of the second block? A) 7.7 kg B) 12 kg C) 5.6 kg D) 21 kg E) 4.4 kg Answer: A Topic: Elastic Collisions 35. A 320-g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 270-g cart. What is the speed of the 270-g cart just after the collision? A) 0.678 m/s B) 0.106 m/s C) 1.36 m/s D) 1.14 m/s E) 2.72 m/s Answer: C Topic: Elastic Collisions 36. A 320-g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 270-g cart. What is the speed of the 320-g cart just after the collision? A) 0.68 m/s B) 0.11 m/s C) 0.21 m/s D) 1.4 m/s E) 1.1 m/s Answer: B Topic: Elastic Collisions 37. In a perfectly elastic collision, a 400-g ball moving toward the east at 3.7 m/s suddenly collides head- on with a 200 g ball sitting at rest. (a) Determine the velocity of the first ball just after the collision. (b) Determine the velocity of the second ball just after the collision. (c) Is kinetic energy conserved in this collision? How do you know? Answer: (a) 1.2 m/s toward the east (b) 4.9 m/s toward the east (c) Yes, it is an elastic collision. Topic: Elastic Collisions Energy and Momentum 38. A 0.140-kg baseball is dropped from rest from a height of 2.20 m above the ground and experiences negligible air resistance as it falls. It rebounds to a height of 1.60 m. What change in the ball's momentum occurs as it rebounds from the ground? A) 0.117 kg ∙ m/s upwards B) 0.117 kg ∙ m/s downwards C) 1.70 kg ∙ m/s upwards D) 0.350 kg ∙ m/s upwards E) 0.350 kg ∙ m/s downwards Answer: C Topic: Energy and Momentum

39. A 0.32-kg ball is moving horizontally at 30 m/s just before suddenly bouncing off a wall Just after the bounce, it is moving horizontally at 25 m/s but in the opposite direction. (a) What is the magnitude of the change in momentum of the ball during the bounce? (b) What percentage of the ball's original kinetic energy was lost in the collision? Answer: (a) 18 N ∙ s (b) 31% Topic: Energy and Momentum 40. A block of mass m = 9.0 kg and speed V and is behind a block of mass M = 27 kg and speed of 0.50 m/s, as shown int the figure. The surface is frictionless, and the blocks suddenly collide and couple. After the collision, the blocks have a common speed of 0.90 m/s. How much kinetic energy of the blocks is lost due to the collision? A) 8.6 J B) 2.0 J C) 4.6 J D) 11 J E) 31 J Answer: A Topic: Energy and Momentum 41. As shown in the figure, a bullet of mass 0.010 kg moving horizontally suddenly strikes a block of wood of mass 1.5 kg that is suspended as a pendulum. The bullet lodges in the wood, and together they swing upward a vertical distance of 0.40 m. The length of the string is 2.0 m. What was the speed of the bullet just before it struck the wooden block? A) 67 m/s B) 250 m/s C) 370 m/s D) 420 m/s E) 650 m/s Answer: D Topic: Energy and Momentum 42. An 8.0-g bullet is suddenly shot into a 4.0-kg block that is at rest on a frictionless horizontal surface, as shown in the figure. The bullet remains lodged in the block. The block then moves against a spring and compresses it by 3.7 cm. The force constant (spring constant) of the spring is 2500 N/m. What was the initial speed v of the bullet? A) 460 m/s B) 440 m/s C) 480 m/s D) 500 m/s E) 520 m/s Answer: A Topic: Energy and Momentum

Energy-Work 1. Person X pushes twice as hard against a stationary brick wall as person Y. Which one of the following statements is correct? A) Both do positive work, but person X does four times the work of person Y. B) Both do positive work, but person X does twice the work of person Y. C) Both do the same amount of positive work. D) Both do zero work. E) Both do positive work, but person X does one-half the work of person Y. Answer: D Topic: Work 2. If the force on an object is in the negative direction, the work it does on the object must be A) negative. B) positive. C) The work could be either positive or negative, depending on the direction the object moves. Answer: C Topic: Work Kinetic Energy 3. A truck has four times the mass of a car and is moving with twice the speed of the car. If K t and K c refer to the kinetic energies of truck and car respectively, it is correct to say that A) K t = 16 K c . B) K t = 4 K c . C) K t = 2 K c . D) K t = K c . E) K t = K c. Answer: A Topic: Kinetic Energy Work-Energy Theorem 4. Three cars (car F, car G, and car H) are moving with the same speed and slam on their brakes. The most massive car is car F, and the least massive is car H. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, which car travels the longest distance to skid to a stop? A) They all travel the same distance in stopping. B) Car F C) Car G D) Car H Answer: A Topic: Work-Energy Theorem

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5. Three cars (car L, car M, and car N) are moving with the same speed and slam on their brakes. The most massive car is car L, and the least massive is car N. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, for which car is the amount of work done by friction in stopping it the greatest? A) The amount of work done by friction is the same for all cars. B) Car L C) Car M D) Car N Answer: B Topic: Work-Energy Theorem 6. Which requires more work, increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph? A) 0 mph to 30 mph B) 50 mph to 60 mph C) It is the same in both cases. Answer: B Topic: Work-Energy Theorem Gravitational Potential Energy 7. You and your friend, who weighs the same as you, want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy of you and your friend, after you both reach the top. A) It is impossible to tell, since the times you both took are unknown. B) It is impossible to tell, since the distances you both traveled are unknown. C) Your friend's gravitational potential energy is greater than yours, because he got to the top faster. D) Both of you have the same amount of gravitational potential energy at the top. E) Your gravitational potential energy is greater than that of your friend, because you traveled a greater distance in getting to the top. Answer: D Topic: Gravitational Potential Energy Energy Conservation with Conservative Forces 8. When you throw a pebble straight up with initial speed V , it reaches a maximum height H with no air resistance. At what speed should you throw it up vertically so it will go twice as high? A) 16 V B) 8 V C) 4 V D) 2 V E) V Answer: E Topic: Energy Conservation with Conservative Forces

9. When you drop a pebble from height H , it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much kinetic energy? A) H B) 2 H C) 4 H D) 8 H E) 16 H Answer: B Topic: Energy Conservation with Conservative Forces 10. Swimmers at a water park have a choice of two frictionless water slides, as shown in the figure. Although both slides drop over the same height h , slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v 1 of a swimmer reaching the bottom of slide 1 compare with v 2 , the speed of a swimmer reaching the end of slide 2? A) v 1 > v 2 B) v 1 < v 2 C) v 1 = v 2 D) The heavier swimmer will have a greater speed than the lighter swimmer, no matter which slide he uses. E) No simple relationship exists between v 1 and v 2 . Answer: C Topic: Energy Conservation With Conservative Forces 11. Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial speed twice as high as Bill. If there is no air resistance, the maximum height of Joe's ball will be A) four times that of Bill's ball. B) two times that of Bill's ball. C) equal to that of Bill's ball. D) eight times that of Bill's ball. E) roughly 1.4 times that of Bill's ball. Answer: A Topic: Energy Conservation With Conservative Forces

12. A stone can slide down one of three different frictionless ramps, as shown in the figure. For which ramp will the speed of the ball be the greatest at the bottom? A) Ramp X B) Ramp Y C) Ramp Z D) The speed of the ball will be the same for all ramps. Answer: D Topic: Energy Conservation With Conservative Forces 13. A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45° above horizontal. Case D: Thrown straight out horizontally. In which case will the speed of the stone be greatest when it hits the water below if there is no significant air resistance? A) Case A B) Case B C) Case C D) Case D E) The speed will be the same in all cases. Answer: E Topic: Energy Conservation With Conservative Forces 14. A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct? (There could be more than one correct choice.) A) Just as they leave the ground, the heavier frog is moving faster than the lighter frog. B) Just as they leave the ground, the lighter frog is moving faster than the heavier frog. C) They both leave the ground with the same speed. D) The lighter frog goes higher than the heavier frog. E) The heavier frog goes higher than the lighter frog. F) Both frogs reach the same maximum height. Answer: B, F Topic: Energy Conservation with Conservative Forces 15. A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct? (There could be more than one correct choice.) A) Both rocks have the same kinetic energy when they reach the ground. B) Both rocks have the same speed when they reach the ground. C) The heavier rock reaches the ground before the lighter rock. D) Just as they were released, both rocks had the same amount of gravitational potential energy. E) When they reach the ground, the heavier rock has more kinetic energy than the lighter rock. Answer: B, E Topic: Energy Conservation with Conservative Forces

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16. A heavy stone and a light stone are released from rest in such away that they both have the same amount of gravitational potential energy just as they are released. Air resistance is negligibly small. Which of the following statements about these stones are correct? (There could be more than one correct choice.) A) The initial height of the light stone is greater than the initial height of the heavy stone. B) The stones must have been released from the same height. C) The stones both have the same speed just as they reach the ground. D) Just as it reaches the ground, the light stone is traveling faster than the heavy stone. E) The stones both have the same kinetic energy just as they reach the ground. Answer: A, D, E Topic: Energy Conservation with Conservative Forces 17. A 1-kg ball is released from a height of 6 m, and a 2-kg ball is released from a height of 3 m. Air resistance is negligible as they fall. Which of the following statements about these balls are correct? (There could be more than one correct choice.) A) As they reach the ground, the 1-kg ball will have more kinetic energy than the 2-kg ball because it was dropped from a greater height. B) As they reach the ground, the 1-kg ball will be moving faster than the 2-kg ball. C) Both balls will reach the ground with the same speed. D) Both balls will reach the ground with the same kinetic energy. E) Both balls will take the same time to reach the ground. Answer: B, D Topic: Energy Conservation with Conservative Forces Energy Conservation with Nonconservative Forces 18. A heavy sled and a light sled, both moving horizontally with the same speed, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them. Which of the following statements about these sleds are correct? (There could be more than one correct choice.) A) Both sleds will slide the same distance on the rough snow before stopping. B) The heavy sled will slide farther on the rough snow than the light sled. C) The light sled will slide farther on the rough snow than the heavy sled. D) The friction from the snow will do more negative work on the heavy sled than on the light sled. E) The friction from the snow will do the same amount of work on both sleds. Answer: A, D Topic: Energy Conservation With Nonconservative Forces 19. A heavy sled and a light sled, both moving horizontally with the same kinetic energy, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them. Which of the following statements about these sleds are correct? (There could be more than one correct choice.) A) Both sleds will slide the same distance on the rough snow before stopping. B) The heavy sled will slide farther on the rough snow than the light sled. C) The light sled will slide farther on the rough snow than the heavy sled. D) On the rough snow, the change in kinetic energy will be the same for both sleds. E) The friction from the snow will do the same amount of work on both sleds. Answer: C, D, E Topic: Energy Conservation With Nonconservative Forces

20. If a stone is dropped with an initial gravitational potential energy of 100 J but reaches the ground with a kinetic energy of only 75 J, this is a violation of the principle of conservation of energy. A) True B) False Answer: B Topic: Energy Conservation With Nonconservative Forces Power 21. If the units of your answer are kg ∙ m 2 /s 3 , which of the following types of quantities could your answer be? (There could be more than one correct choice.) A) kinetic energy B) potential energy C) force D) power E) work Answer: D Topic: Power 22. Two cyclists who weigh the same and have identical bicycles ride up the same mountain, both starting at the same time. Joe rides straight up the mountain, and Bob rides up the longer road that has a lower grade. Joe gets to the top before Bob. Ignoring friction and wind resistance, which one of the following statements is true? A) The amount of work done by Joe is equal to the amount of work done by Bob, but the average power exerted by Joe is greater than that of Bob. B) The amount of work done by Joe is greater than the amount of work done by Bob, and the average power exerted by Joe is greater than that of Bob. C) Bob and Joe exerted the same amount of work, and the average power of each cyclist was also the same. D) The average power exerted by Bob and Joe was the same, but Joe exerted more work in getting there. Answer: A Topic: Power Work 23.: How much work would a child do while pulling a 12-kg wagon a distance of 4.3 m with a 22 N force? A) 95 J B) 52 J C) 66 J D) 109 J Answer: A Topic: Work 24. A child does 350 J of work while pulling a box from the ground up to his tree house at a steady speed with a light rope. The tree house is 4.0 m above the ground. What is the mass of the box? A) 8.9 kg B) 5.3 kg C) 6.7 kg D) 8.0 kg Answer: A Topic: Work

25. You carry a 7.0-kg bag of groceries 1.2 m above the ground at constant speed across a 2.7 m room. How much work do you do on the bag in the process? A) 0.00 J B) 82 J C) 185 J D) 157 J Answer: A Topic: Work 26. A crane lifts a 425 kg steel beam vertically upward a distance of 95 m. How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s 2 ? Neglect frictional forces. A) 4.7 × 10 5 J B) 2.7 × 10 5 J C) 3.2 × 10 5 J D) 4.0 × 10 5 J Answer: A Topic: Work 27. A traveler pulls on a suitcase strap at an angle 36° above the horizontal. If 555 J of work are done by the strap while moving the suitcase a horizontal distance of 15 m, what is the tension in the strap? A) 46 N B) 37 N C) 52 N D) 56 N Answer: A Topic: Work 28. A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. (a) What is the work done by the 5500-N force? (b) What is the work done by gravity? (c) What is the net work done on the elevator? Answer: (a) 275 Kj (b) -245 kJ (c) 30.0 kJ Topic: Work 29. A person carries a 25.0-N rock through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 1.50 min. How much work did gravity do on the rock between A and B? A) 625 J B) 20.0 J C) 275 J D) 75 J E) 0 J Answer: E Topic: Work

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Kinetic Energy 30. How fast must a 6.0-kg cat run to have a kinetic energy of 150 J? Answer: 7.1 m/s Topic: Kinetic Energy 31. How much kinetic energy does a 0.30-kg stone have if it is thrown at 44 m/s? A) 290 J B) 580 J C) 440 J D) 510 J Answer: A Topic: Kinetic Energy 32. An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy of the object? A) 1/2 B) 1/4 C) 1/8 D) 1/16 Answer: B Topic: Kinetic Energy Work-Energy Theorem 33. When a car of mass 1167 kg accelerates from 10.0 m/s to some final speed, 4.00 × 10 5 J of work are done. Find this final speed. A) 28.0 m/s B) 22.4 m/s C) 25.2 m/s D) 30.8 m/s Answer: A Topic: Work-Energy Theorem 34. How large a net force is required to accelerate a 1600-kg SUV from rest to a speed of 25 m/s in a distance of 200 m? A) 1600 N B) 0 N C) 200 N D) 400 N E) 2500 N Answer: E Topic: Work-Energy Theorem

35. A sled having a certain initial speed on a horizontal surface comes to rest after traveling 10 m. If the coefficient of kinetic friction between the object and the surface is 0.20, what was the initial speed of the object? A) 9.8 m/s B) 6.3 m/s C) 3.6 m/s D) 7.2 m/s E) 8.9 m/s Answer: B Topic: Work-Energy Theorem 36. A certain car traveling at 34.0 mph skids to a stop in 29 meters from the point where the brakes were applied. In approximately what distance would the car have stopped had it been going 105.4 mph? A) 279 m B) 158 m C) 90 m D) 51 m E) 29 m Answer: A Topic: Work-Energy Theorem Gravitational Potential Energy 37. How high a hill would a 75-kg hiker have to climb to increase her gravitational potential energy by 10,000 J? Answer: 14 m Topic: Gravitational Potential Energy 38. You do 116 J of work while pulling your sister back on a frictionless swing, whose chain is 5.10 m long, until the swing makes an angle of 32.0° with the vertical. What is your sister's mass? A) 15.3 kg B) 13.0 kg C) 17.6 kg D) 19.0 kg Answer: A Topic: Gravitational Potential Energy 39. A tennis ball bounces on the floor three times, and each time it loses 23.0% of its energy due to heating. How high does it bounce after the third time, if we released it 4.0 m from the floor? A) 180 cm B) 18 cm C) 180 mm D) 240 cm Answer: A Topic: Gravitational Potential Energy

Springs 40. A 10-kg mass, hung by an ideal spring, causes the spring to stretch 2.0 cm. What is the spring constant (force constant) for this spring? A) 5.0 N/cm B) 49 N/cm C) 0.20 N/cm D) 20 N/m E) 0.0020 N/cm Answer: B Topic: Springs 41. An ideal spring stretches by 21.0 cm when a 135-N object is hung from it. If instead you hang a fish from this spring, what is the weight of a fish that would stretch the spring by 31.0 cm? A) 199 N B) 91 N C) 145 N D) 279 N Answer: A Topic: Springs 42. An ideal spring has a spring constant (force constant) of 2500 N/m. is stretched 4.0 cm. How much work is required to stretch the spring by 4.0 cm? A) 4.0 J B) 0.00 J C) 1.0 J D) 3.0 J E) 2.0 J Answer: E Topic: Springs Energy Conservation with Conservative Forces 43.: A rock falls from a vertical cliff that is 4.0 m tall and experiences no significant air resistance as it falls. At what speed will its gravitational potential energy (relative to the base of the cliff) be equal to its kinetic energy? A) 3.1 m/s B) 4.4 m/s C) 6.3 m/s D) 8.9 m/s E) 13 m/s Answer: C Topic: Energy Conservation with Conservative Forces

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44. A block slides down a frictionless inclined ramp and experiences no significant air resistance. If the ramp angle is 17.0° above the horizontal and the length of the surface of the ramp is 20.0 m, find the speed of the block as it reaches the bottom of the ramp, assuming it started sliding from rest at the top. A) 10.7 m/s B) 114 m/s C) 7.57 m/s D) 19.6 m/s Answer: A Topic: Energy Conservation with Conservative Forces 45. A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C? A) 0 m/s B) 34 m/s C) 69 m/s D) 20 m/s E) We cannot solve this problem without knowing the mass of the bead. Answer: B Topic: Energy Conservation with Conservative Forces 46. What is the minimum energy needed to lift a 1.0-kg rocket to a height of 200 km and to give it a speed of 8.0 km/s at that height? (Neglect air resistance and the small decrease in g over that distance.) A) 34 TJ B) 34 kJ C) 34 MJ D) 34 GJ E) 34 J Answer: C Topic: Energy Conservation With Conservative Forces 47. Assuming negligible friction, what spring constant (force constant) would be needed by the spring in a "B-B gun" to fire a 10-g pellet to a height of 100 m if the spring is initially compressed by 0.10 m? A) 20 N/cm B) 20 N/m C) 200 N/m D) 2000 N/cm E) 0.0020 N/m Answer: A Topic: Energy Conservation with Conservative Forces

48. In the figure, a ball hangs by a very light string. What is the minimum speed of the ball at the bottom of its swing (point B) in order for it to reach point A, which is 1.0 m above the bottom of the swing? A) 2.2 m/s B) 3.1 m/s C) 4.4 m/s D) 4.9 m/s Answer: C Topic: Energy Conservation With Conservative Forces 49. A roller coaster starts from rest at a height h at the left side of a loop-the-loop, as shown in the figure. It is not attached to the track in anyway, and there is no friction from the track or from air resistance. If the radius of the loop is R = 6.0 m, what is the minimum height h for which the roller coaster will not fall off the track at the top of the loop? A) 21 m B) 18 m C) 15 m D) 12 m E) 8.5 m Answer: C Topic: Energy Conservation With Conservative Forces Energy Conservation with Nonconservative Forces 50. A 30-N stone is dropped from a height of 10 m and strikes the ground with a speed of 13 m/s. What average force of air friction acted on the stone as it fell? A) 4.1 N B) 2.9 N C) 0.13 kN D) 7.2 N E) 1.2 N Answer: A Topic: Energy Conservation With Nonconservative Forces 51. A 60-kg skier starts from rest from the top of a 50-m high slope. If the work done by friction is -6.0 kJ, what is the speed of the skier on reaching the bottom of the slope? A) 17 m/s B) 24 m/s C) 28 m/s D) 31 m/s Answer: C Topic: Energy Conservation with Nonconservative Forces

52. A 7.5-kg otter slides down a hill, starting from rest at the top. The sloping surface of the hill is 8.8 m long, and the top is 6.5 m above the base. If the speed of the otter at the bottom of the hill is 9.2 m/s, how much energy was lost to nonconservative forces on the hill? Answer: 160 J Topic: Energy Conservation With Nonconservative Forces 53. An object with a mass of 10 kg is initially at rest at the top of a frictionless inclined plane that rises at 30° above the horizontal. At the top, the object is initially 8.0 m from the bottom of the incline, as shown in the figure. When the object is released from this position, it eventually stops at a distance d from the bottom of the inclined plane along a horizontal surface, as shown. There is friction on the horizontal portion. The coefficient of kinetic friction between the horizontal surface and the object is 0.20, and air resistance is negligible. Find the distance d . A) 5.0 m B) 10 m C) 15 m D) 20 m E) 25 m Answer: D Topic: Energy Conservation With Nonconservative Forces 54. A 0.12-kg block is held in place against the spring by a 35-N horizontal external force. The external force is removed, and the block is projected with a velocity v 1 = 1.2 m/s when it separates from the spring, as shown in the figure. The block descends a ramp and has a velocity v 1 = 1.4 m/s at the bottom of the ramp. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction between the block and the rough surface is 0.26. The block moves on to D, where it stops. By how many centimeters was the spring initially compressed? A) 0.49 cm B) 0.26 cm C) 0.18 cm D) 0.99 cm E) 0.67 cm Answer: A Topic: Energy Conservation With Nonconservative Forces Power 55. How many joules of energy are used by a 2.0 hp motor that runs for 1.0 hour? (1 hp = 746 W) Answer: 5.4 MJ Topic: Power 55. A child pulls on a wagon with a force of 75 N. If the wagon moves a total of 42 m in 3.1 min, what is the average power delivered by the child? A) 17 W B) 21 W C) 22 W D) 26 W Answer: A Topic: Power

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