Chapter 6 Review

13. The 12-ounce boxing gloves used in amateur fights hurt less than the 6-ounce gloves used in professional fights because the ____ stopping times mean ____ forces. A. increased ... smaller B. decreased ... smaller C. increased ... larger D. decreased ... larger

A

16. An astronaut training at the Craters of the Moon in Idaho jumps off a platform in full spacewalk gear and hits the surface at 5 m/s. If later on the Moon the astronaut jumps from the LEM and hits the surface at the same speed, the impulse will be ____ that on Earth. A. the same as B. larger than C. smaller than

A

18. A clay ball and a rubber ball have equal mass. A student releases each ball from rest at the same height. The clay ball sticks to the ground while the rubber ball bounces back up. The magnitude of the impulse delivered to the rubber ball by the floor is A. greater than that delivered to the clay ball by the floor B. less than that delivered to the clay ball by the floor C. equal to that delivered to the clay ball by the floor

A

30. A coach is hitting pop flies to the outfielders. If the baseball (m = 145 g) stays in contact with the bat for 0.04 s and leaves the bat with a speed of 50 m/s, what is the average force acting on the ball? A. 181 N B. 290 N C. 56,400 N D. 181,000 N

A

34. If rockets are fired from an airplane in the forward direction, the momentum of the airplane will A. decrease. B. be unchanged. C. increase.

A

36. We can explain the recoil that occurs when a rifle is fired by using the conservation of A. momentum. B. kinetic energy. C. work. D. mass.

A

42. Larry has a mass of 90 kg and runs across the front of the classroom with a speed of 5 m/s and jumps onto a giant skateboard. The skateboard is initially at rest and has a mass equal to Larry's. If we ignore friction with the floor, what is the speed of Larry and the skateboard? A. 2.5 m/s B. 5 m/s C. 45 m/s D. 450 m/s

A

46. A 5-kg cart moving at 2 meters per second hits a stationary 5-kg cart. The two move off together at 1 meter per second. Paula contends, "Momentum is conserved in this collision because the momentum of the system has the same value before and after the collision." Lillian counters, "The momentum of the system before the collision is 10 kilogram-meters per second, not zero, so momentum is not conserved." As a "momexpert," you should A. Agree entirely with Paula, Lillian's argument is irrelevant B. Agree mostly with Paula, but Lillian makes a relevant point C. Agree equally with Paula and Lillian D. Agree mostly with Lillian, but Paula makes a relevant point

A

53. Exhibit 6-1 A friend is making an iMovie and wants your help designing a skateboard stunt. You estimate that your friend's mass is four times greater than that of the skateboard. For the following questions, ignore friction. Refer to Exhibit 6-1. In one scenario, the skateboard starts at rest and your friend jumps horizontally onto it. In order for the skateboard/person system to have a final speed of 6 meters per second, your friend must jump at a speed of A. 6 meters per second B. 7.2 meters per second C. 7.5 meters per second D. 24 meters per second

A

56. A 3-kg ball traveling to the right with a speed of 4 m/s collides with a 4-kg ball traveling to the left with a speed of 3 m/s. What is the total momentum of the two balls before and after the collision? A. zero B. 12 kg·m/s C. 24 kg·m/s D. The momentum will be different before and after the collision.

A

57. A 4-kg ball traveling to the right with a speed of 4 m/s collides with a 5-kg ball traveling to the left with a speed of 2 m/s. What is the total momentum of the two balls after they collide? A. 6 kg·m/s to the right B. 22 kg·m/s to the right C. 26 kg·m/s to the right D. 40 kg·m/s to the right

A

63. Two students are arguing in physics lab about an experiment in which two gliders collide on a frictionless air track. Glider A hits glider B, which is twice as massive and initially stationary. Wilson claims "Glider B will have the largest final speed when glider A's final speed is zero. In that case, A gives all of its momentum to B." Grady counters "Glider A will experience a greater change in momentum if it bounces back, rather than if it stops. Thus glider B will have a faster final speed if A bounces back." As the third member of the lab team, you should A. disagree with Wilson, and point out that he is not taking the vector nature of momentum into account B. disagree with Grady, and point out that he is not taking conservation of momentum into account C. disagree with both of your partners D. there is not enough information to predict how the final speed of glider B will compare in these two scenarios

A

8. How fast would an 80-kg person need to run to have the same momentum as an 18-wheeler (m = 24,000 kg) rolling along at 1 mph? A. 300 mph B. 3000 mph C. 1,920 mph D. 1,920,000 mph

A

1. Under what conditions is mass conserved? A. Only when the change is a chemical one. B. Only when the change is a physical one. C. Whenever the system is isolated or closed. D. Always.

C

12. Air bags are used by stunt people when they fall off buildings to reduce the ____ that occurs during the collision. A. change in momentum B. impulse C. force D. change in velocity

C

14. Why is skiing into a wall of deep powder less hazardous to your health than skiing into a wall of bricks? Assume in both cases that you have the same initial speed and come to a complete stop. A. The change in momentum is less in powder. B. The impulse is less in powder. C. The increased stopping time in powder means a smaller stopping force. D. The decreased stopping time in powder means a larger stopping force.

C

15. A tailgunner jumped from a Lancaster bomber but did not break any bones or die because he fell into the branches of a tree and then into a snow bank. Physics explains this because A. the change in momentum was less than hitting the ground directly. B. the impulse in less in trees and snow than ground. C. the increased stopping time in the tree meant a smaller stopping force. D. the decreased stopping time in the tree meant a smaller stopping force.

C

17. Assuming that your author jumps off the roof of a garage and lands on the ground, how will the impulse the ground exerts on him if he lands on grass compare to that if he lands on concrete? A. The impulse will be larger if he lands on concrete. B. The impulse will be larger if he lands on grass. C. The impulses will be the same independent of the surface.

C

19. A clay ball is released from rest, falls, and sticks to the floor. The magnitude of the impulse that gravity imparts to the ball during is fall is _________ the magnitude of the impulse that the floor imparts to the ball during the stop. A. much greater than B. much less than C. about equal to

C

2. Which has the greater momentum, a heavy truck at rest or a moving roller skate? A. Cannot tell from the information given. B. the heavy truck C. the roller skate D. The momenta are equal.

C

22. Which of the following will cause the largest change in the momentum of an object? A force of ____ acting for ____. A. 3 N ... 6 s B. 4 N ... 5 s C. 5 N ... 5 s D. 6 N ... 3 s

C

26. A 1400-kg car has a speed of 20 m/s. What average force is required to stop the car in 10 s? A. 70 N B. 700 N C. 2800 N D. 280,000 N

C

29. It takes about 30 s for a jet plane to go from rest to the takeoff speed of 100 mph (44.7 m/s). What is the average horizontal force that the seat exerts on the back of a 80-kg passenger during takeoff? A. 16.8 N B. 53.7 N C. 119 N D. 11,300 N

C

31. A tennis ball (m = 0.2 kg) is thrown at a brick wall. It is traveling horizontally at 16 m/s just before hitting the wall and rebounds from the wall at 8 m/s, still traveling horizontally. The ball is in contact with the wall for 0.04 s. What is the magnitude of the average force of the wall on the ball? A. 40 N B. 80 N C. 120 N D. 640 N

C

38. An astronaut floating in the center of the main room in SkyLab with no translational motion relative to Skylab A. can get to a wall by waving his arms and legs. B. can convert his rotational motion to translational motion. C. is stranded. D. cannot change his orientation.

C

39. Greg runs across the front of the classroom with a momentum of 300 kg·m/s and jumps onto a giant skateboard. The skateboard is initially at rest and has a mass equal to Greg's. If we ignore friction with the floor, what is the total momentum of Greg and the skateboard? A. zero B. 150 kg·m/s C. 300 kg·m/s D. 600 kg·m/s

C

43. Juan has a mass of 60 kg and is standing on a giant skateboard that is initially at rest and has a mass of 30 kg. If we ignore frictional effects with the floor, what is the speed of the skateboard if Juan walks to the right with a speed of 3 m/s? A. 1 m/s B. 3 m/s C. 6 m/s D. 600 m/s

C

5. If a sports car with a mass of 1000 kg travels down the road with a speed of 30 m/s, its momentum is 30,000 A. kg/(m/s) B. kg·s/m C. kg·m/s D. kg·m2/s2

C

51. A 3-kg ball traveling to the right with a speed of 4 m/s overtook and collided with a 4-kg ball traveling in the same direction with a speed of 2 m/s. The total momentum after the collision was ____ kg·m/s to the right. A. 8 B. 12 C. 20 D. 96

C

54. Exhibit 6-1 A friend is making an iMovie and wants your help designing a skateboard stunt. You estimate that your friend's mass is four times greater than that of the skateboard. For the following questions, ignore friction. Refer to Exhibit 6-1. In one scenario, your friend starts by standing at rest on the skateboard, and then jumps horizontally off of the skateboard. In order for the skateboard to shoot out with a speed of 10 meters per second, how fast should your friend jump (relative to the ground)? A. 10 meters per second B. 2 meters per second C. 2.5 meters per second D. 25 meters per second

C

55. Exhibit 6-1 A friend is making an iMovie and wants your help designing a skateboard stunt. You estimate that your friend's mass is four times greater than that of the skateboard. For the following questions, ignore friction. Refer to Exhibit 6-1. In one scenario, your friend the skateboard will coast across a horizontal surface at a constant speed of 10 meters per second. Your friend will then drop vertically from a ledge, landing squarely on the skateboard. Your friend wants the skateboard to end up with a speed of 1.8 meters per second after the drop. Will it work? A. Yes, it will work as described above. B. No, it will not work. Your friend needs to "add some mass," and could wear a backpack with some bricks in it to make the stunt work as described. C. No, it will not work. The skateboard needs to "add some mass," so your friend could tape some bricks to the skateboard to make the stunt work as described.

C

6. If a sports car with a mass of 1000 kg travels down the road with a speed of 40 m/s, its momentum is A. 100 kg/m/s B. 20,000 kg·m/s C. 40,000 kg·m/s D. 400,000 kg·m2/s2

C

61. A puck is traveling along a frictionless horizontal surface at constant speed. The magnitude of the puck's momentum is 10 kg·m/s. The puck then separates into two equal size pieces, each of which moves off at a 20 degree angle to the puck's initial path. The magnitude of the momentum of each piece is A. less than 5 kg·m/s B. equal to 5 kg·m/s C. more than 5 kg·m/s

C

62. Two cars of identical mass travel at the same constant speed. One car is moving in a direction 10 degrees east of due north while the other car is moving in a direction 10 degrees west of due north. The cars collide and stick together, moving due north just after the collision. Just after the collision, the magnitude of the momentum of the two car system is A. twice as great as that of a single car just before the collision B. more than twice as great as that of a single car just before the collision C. less than twice as great as that of a single car just before the collision

C

7. How fast would you have to throw a baseball (m = 145 g) to give it the same momentum as a 10-g bullet traveling at 800 m/s? A. 0.55 m/s B. 1.8 m/s C. 55 m/s D. 800 m/S

C

9. Newton's second law can be rearranged to show that the ____ is equal to the ____. A. momentum ... impulse B. change in momentum ... change in impulse C. change in momentum ... impulse D. momentum ... change in impulse

C

10. Padded dashboards in automobiles are safer because the A. momentum change is less B. impulse is less C. impact time is less D. impact time is greater

D

11. The stunt person who is shot by a bandit and falls from the balcony into an air bag rather than onto the ground will not be hurt because the A. momentum change is less for the air bag. B. momentum is less for the air bag. C. impulse is less for the air bag. D. increased stopping time means a smaller stopping force.

D

23. What is the impulse of a 5 N force acting for 15 s? A. 3 N·s B. 15 N·s C. 20 N·s D. 75 N·s

D

24. What change in momentum occurs when a force of 20 N acts for 4 s? A. 5 kg·m/s B. 16 kg·m/s C. 24 kg·m/s D. 80 kg·m/s

D

25. What impulse is need to stop a 1200-kg car traveling at 20 m/s? A. 60 N·s B. 240 N·s C. 1200 N·s D. 24,000 N·s

D

27. What average force is required to stop a 120-kg football player running at 8 m/s in a time of 0.4 s? A. 6 N B. 37.5 N C. 384 N D. 2400 N

D

32. A very hard rubber ball (m = 0.6 kg) is falling vertically at 6 m/s just before it bounces on the floor. The ball rebounds back at essentially the same speed. If the collision with the floor lasts 0.04 s, what is the average force exerted by the floor on the ball? A. 45 N B. 90 N C. 180 N D. 360 N

D

33. If we examine a ball in free fall, we find that the momentum of the ball is not constant. This is not a violation of the law of conservation of momentum because A. the force of gravity acts on the ball. B. the ball experiences an external force. C. the system is not closed. D. All of the above.

D

35. We can explain the recoil that occurs when a rifle is fired by using A. conservation of momentum. B. equal and opposite impulses. C. equal and opposite changes in momentum D. Any of the above.

D

41. Two air-track gliders are held together with a string. The mass of glider A is twice that of glider B. A spring is tightly compressed between the gliders. If the gliders are initially at rest and the spring is released by burning the string, what is the total momentum of both gliders after the release? A. twice the momentum of A B. half the momentum of A C. twice the momentum of B D. zero

D

45. Two identical carts with identical speeds collide head-on and stick together. Greg argues, "Momentum for this system is conserved because the moemtnum of the first cart cancles the moemtnum of the second cart to give zero." Andrew responds, "No, momentum is conserved because it is zero both before and after the collision." As a "momexpert," you should A. Agree entirely with Greg,Andrew's argument is irrelevant B. Agree mostly with Greg, but Andrew makes a relevant point C. Agree equally with Greg and Andrew D. Agree entirely with Andrew, Greg's argument is irrelevant

D

47. A cue ball hits a stationary eight ball on a pool table. For which of the following systems is there a change in momentum during the collision? A. the cue ball B. the eight ball C. the system consisting of both balls together D. a and b

D

48. A rambunctious little girl kicks a soccer ball into a lamppost. Luckily, the post is very solidly planted and does not move. For which of the following systems is there a change in momentum during the collision? A. the soccer ball B. the lamppost C. the system consisting of the soccer ball and the lamppost D. a and c

D

49. A 2-kg ball traveling to the right with a speed of 3 m/s collides with a 4-kg ball traveling to the left with a speed of 2 m/s. The total momentum of the two balls after the collision is ____ kg-m/s to the ____. A. 14 ... left B. 14 ... right C. 2 ... right D. 2 ... left

D

50. A 2-kg ball traveling to the right with a speed of 4 m/s collides with a 4-kg ball traveling to the left with a speed of 2 m/s. The total momentum of the two balls after the collision is A. 16 kg·m/s to the left B. 16 kg·m/s to the right C. 2 kg·m/s to the right D. zero

D

52. A father (m = 90 kg) and son (m = 45 kg) are standing facing each other on a frozen pond. The son pushes on the father and finds himself moving backward at 3 m/s after they have separated. How fast is the father moving? A. 1 m/s B. 1.5 m/s C. 3 m/s D. 6 m/s

D

58. A 1200-kg car traveling north at 14 m/s is rear-ended by a 2000-kg truck traveling at 25 m/s. What is the total momentum before and after the collision? A. 16,800 kg·m/s B. 33,200 kg·m/s C. 62,400 kg·m/s D. 66,800 kg·m/s

D

59. A 1200-kg car traveling north at 14 m/s is rear-ended by a 2000-kg truck traveling at 25 m/s. If the truck and car lock bumpers and stick together, what is their speed immediately after the collision? A. 5.25 m/s B. 10.4 m/s C. 19.5 m/s D. 20.9 m/s

D

20. A rubber ball is released from rest, falls, and bounces back up. The magnitude of the impulse that gravity imparts to the ball during is fall is _________ the magnitude of the impulse that the floor imparts to the ball during the bounce. A. much greater than B. much less than C. about equal to

B

21. A rubber ball is thrown against a horizontal wall and bounces back with the same speed it came in at. The change in momentum vector of the ball is A. in the same direction as the ball's initial motion B. in the opposite direction as the ball's initial motion C. is zero

B

28. What average net force is needed to accelerate a 1200-kg car to a speed of 30 m/s in a time of 8 s? A. 320 N B. 4500 N C. 144,000 N D. 288,000 N

B

3. Which has the greater momentum, an 18-wheeler parked at the curb or a Volkswagen rolling down a hill? A. 18-wheeler B. Volkswagen C. The momenta are equal. D. Could be either.

B

37. What happens to the total momentum of a star that undergoes a supernova explosion? A. It increases. B. It remains constant. C. It decreases. D. It depends on the color of the star.

B

4. Linear momentum is defined to be A. mass times speed. B. mass times velocity. C. mass times acceleration. D. weight times velocity.

B

40. Carmen is standing on a giant skateboard that is initially at rest. If we ignore frictional effects with the floor, what is the momentum of the skateboard if Carmon walks to the right with a momentum of 500 kg·m/s? A. 500 kg·m/s to the right B. 500 kg·m/s to the left C. 500 kg·m/s D. zero

B

44. Two air-track gliders are held together with a string. The mass of glider A is twice that of glider B. A spring is tightly compressed between the gliders. The gliders are initially at rest and the spring is released by burning the string. If glider B has a speed of 3 m/s after the release, how fast will glider A be moving? A. 1 m/s B. 1.5 m/s C. 3 m/s D. 6 m/s

B

60. A boxcar traveling at 10 m/s approaches a string of three identical boxcars sitting stationary on the track. The moving boxcar collides and links with the stationary cars, and the four move off together along the track. What is the final speed of the four cars immediately after the collision? (You may take the mass of each boxcar to be 18,537 kg.) A. 2 m/s B. 2.5 m/s C. 3.33 m/s D. 10 m/s

B