3. Physics Practice Questions Chapter 6

1) Which of the following has the largest momentum relative to the Earth? A) a tightrope walker crossing Niagara Falls B) a pickup truck speeding along a highway C) a Mack truck parked in a parking lot D) the Science building on campus E) a dog running down the street

B

21) A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared to the force that stops the car, the force needed to stop the truck is A) greater. B) smaller. C) the same.

A

24) A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both move with a combined momentum of A) less than 1 unit. B) more than 1 unit. C) 1 unit. D) not enough information.

C

28) Compared to the force that brings a small car to a stop, the force required to bring a heavy truck traveling at the same speed to a stop A) is less. B) is more. C) may be less and may be more.

C

34) A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is A) 1/2 m/s. B) 2/5 m/s. C) 5/6 m/s. D) 6/5 m/s. E) 1 m/s.

C

35) A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the larger fish after lunch is A) 1/2 m/s. B) 1/5 m/s. C) 1/6 m/s. D) 2/3 m/s. E) 3/2 m/s.

C

36) A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball that is initially at rest. The bowling ball and putty are then in motion with a speed of A) 1/4 m/s. B) 1/5 m/s. C) 1/6 m/s. D) none of these. E) not enough information given.

C

46) A 1-kg glider and a 2-kg glider both slide toward each other at 1 m/s on an air track. They collide and stick. The combined mass moves at A) 0 m/s. B) 1/2 m/s. C) 1/3 m/s. D) 1/6 m/s. E) 1.5 m/s.

C

48) A 5000-kg freight car runs into a 10,000-kg freight car at rest. They couple upon collision and move with a speed of 2 m/s. What was the initial speed of the 5000-kg car? A) 4 m/s B) 5 m/s C) 6 m/s D) 8 m/s E) none of these

C

49) A 5000-kg freight car moving at 2 m/s runs into a 10,000-kg freight car at rest. They couple upon collision and move away as one body at A) 2 m/s. B) 1 m/s. C) 2/3 m/s. D) 1/3 m/s.

C

5) The conservation of momentum is most closely related to A) Newton's 1st law. B) Newton's 2nd law. C) Newton's 3rd law.

C

9) A heavy truck and a small truck roll down a hill. Neglecting friction, at the bottom of the hill, the heavy truck will have greater A) speed. B) acceleration. C) momentum. D) all of these. E) none of these.

C

10) In order to catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball's motion upon impact. Doing this reduces the force of impact on the player's hand principally because the A) force of impact is reduced. B) relative velocity is less. C) time of impact is increased. D) time of impact is decreased. E) none of these.

C

12) When you are in the way of a fast-moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a A) long time. B) short time. C) same way either way.

A

18) A 4 kg ball has a momentum of 12 kg m/s. What is the ball's speed? A) 3 m/s B) 4 m/s C) 12 m/s D) 48 m/s E) none of these

A

20) Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be A) zero. B) the same as before. C) small, but noticeable.

A

27) Two billiard balls having the same mass roll toward each other, each moving at the same speed. What is the combined momentum of the two balls? A) 0 kg m/s. B) 10 kg m/s. C) more information need to determine.

A

38) A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact. The boat can A) then move in the direction of the wind impact force. B) not move by this wind impact. C) then move, but in the opposite direction of the wind impact force.

A

43) If the ball is one hundredth as massive as the astronaut, the time between catches A) increases as the game progresses. B) stays the same as the game progresses. C) decreases as the game progresses.

A

47) Two identical gliders slide toward each other on an air track. One moves at 1 m/s and the other at 2 m/s. They collide and stick. The combined mass moves at A) 1/2 m/s. B) 1/3 m/s. C) 1/6 m/s. D) 3/4 m/s. E) 1.5 m/s.

A

7) Suppose a gun were made of a strong but very light material. Suppose also that the bullet is more massive than the gun itself. For such a weapon A) the target would be safer than the shooter. B) recoil problems would be lessened. C) conservation of energy would not hold. D) conservation of momentum would not hold. E) both conservation of energy and momentum would not hold.

A

17) Compared to falling on a wooden floor, a wine glass may not break when it falls to a carpeted floor because of the A) lesser impulse in stopping. B) longer time to stop. C) both of these. D) neither of these.

B

19) A ball is moving at 4 m/s and has a momentum of 48 kg m/s. What is the ball's mass? A) 4 kg B) 12 kg C) 48 kg D) 192 kg E) none of these

B

2) The difference between impulse and impact force involves the A) distance the force acts. B) time the force acts. C) difference between acceleration and velocity. D) mass and its effect on resisting a change in momentum.

B

25) A 1-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-kg bowling ball initially at rest. The bowling ball and putty then move with a momentum of A) 0 kg m/s. B) 1 kg m/s. C) 2 kg m/s. D) 5 kg m/s. E) more than 5 kg m/s.

B

29) A cannonball shot from a cannon with a long barrel will have a greater muzzle velocity because the cannonball receives a greater A) force. B) impulse. C) both of these. D) neither of these.

B

3) It is correct to say that impulse is equal to A) momentum. B) the change in momentum. C) the force multiplied by the distance the force acts. D) all of these. E) none of these.

B

31) A 1000-kg car moving at 10 m/s brakes to a stop in 5 s. The average braking force is A) 1000 N. B) 2000 N. C) 3000 N. D) 4000 N. E) 5000 N.

B

37) Momentum is transferred to the ground when an apple falls on it. The momentum absorbed by the ground is A) negligible compared to the momentum of the apple. B) greater than that of the apple only if the apple bounces. C) greater than that of the apple in all cases. D) none of these.

B

39) If all people, animals, trains and trucks all over the world began to walk or run towards the east, then the A) earth would spin a bit faster. B) earth would spin a bit slower. C) earth's spin would not be affected at all.

B

4) The impulse-momentum relationship is a direct result of A) Newton's 1st law. B) Newton's 2nd law. C) Newton's 3rd law.

B

41) If the ball is as massive as the astronaut, the A) astronaut will catch one bounce only. B) astronaut will never catch the first bounce. C) astronaut's time between catches will decrease as the game progresses. D) none of these.

B

44) A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of A) less than 1 unit. B) more than 1 unit. C) 1 unit. D) not enough information.

B

11) When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. In this way the average force your body experiences is A) less than 1/10 as great. B) more than 1/10 as great. C) about 1/10 as great. D) about 10 times as great.

C

30) According to the impulse-momentum equation Ft = change in (mv), a person will suffer less injury falling on a wooden floor which "gives" than on a more rigid cement floor. The "F" in the above equation stands for the force exerted on the A) person. B) floor. C) both of these. D) none of these.

C

32) Which would be more damaging, driving into a very massive concrete wall with no "give," or having a head-on collision at the same speed with an identical car moving toward you with the same speed? It would be more damaging to hit the A) car. B) wall. C) both the same.

C

40) You're driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum? A) the bug B) your car C) both the same

C

42) If the ball is as massive as the astronaut, the distance between the moving ball and the moving astronaut after the first bounce A) increases with time. B) decreases with time. C) remains constant with time.

C

45) Consider massive gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1 kg, a speed of 1 m/s, and collides with Glider B that has a mass of 5 kg and is at rest. If they stick upon collision, their speed after collision will be A) 1/4 m/s. B) 1/5 m/s. C) 1/6 m/s. D) 1 m/s. E) none of these.

C

6) A rifle recoils from firing a bullet. The speed of the rifle's recoil is small because the A) force against the rifle is smaller than against the bullet. B) momentum is mainly concentrated in the bullet. C) rifle has much more mass than the bullet. D) momentum of the rifle is smaller.

C

8) Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a greater A) speed. B) acceleration. C) momentum. D) all of these. E) none of these.

C

14) A bullet is fired from a gun. The speed of the bullet will be about the same as the speed of the recoiling gun A) because momentum is conserved. B) because velocity is conserved. C) because both velocity and momentum are conserved. D) if the mass of the bullet equals the mass of the gun. E) none of these.

D

16) The force on an apple hitting the ground depends upon A) the speed of the apple just before it hits. B) the time of impact with the ground. C) whether or not the apple bounces. D) all of these.

D

23) A karate expert executes a swift blow and severs a cement block with her bare hand. The magnitude is the same for the A) impulse on both the block and the expert's hand B) force on both the block and the expert's hand. C) time of impact on both the block and the expert's hand. D) all of these. E) none of these.

D

26) The force that accelerates a rocket in outer space is exerted on the rocket by the A) rocket's engine. B) rocket's wings. C) atmospheric pressure. D) exhaust gases. E) none of these.

D

33) A rifle of mass 2 kg is suspended by strings. The rifle fires a bullet of mass 1/100 kg at a speed of 200 m/s. The recoil velocity of the rifle is about A) 0.001 m/s. B) 0.01 m/s. C) 0.1 m/s. D) 1 m/s. E) none of these.

D

13) A car traveling along the highway needs a certain amount of force exerted on it to stop it in a certain distance. More stopping force is required when the car has A) more mass. B) more momentum. C) less stopping distance. D) all of these. E) none of these.

E

15) Padded dashboards in cars are safer in an accident than nonpadded ones because an occupant hitting the dash has A) increased time of impact. B) decreased impulse. C) decreased impact force. D) a and b above. E) a and c above.

E

22) A 1-N apple falls to the ground. The apple hits the ground with an impact force of about A) 1 N. B) 2 N. C) 4 N. D) 9.8 N. E) not enough information given to say.

E

50) A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it. They stick together and move at a speed of A) 3 m/s. B) 4 m/s. C) 6 m/s. D) 8 m/s. E) none of these

E