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1) A rock is dropped from a high tower and falls freely under the influence of gravity

Physics

1) A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements is true concerning the rock as it falls?

    1. It will gain an equal amount of momentum during each second.
    2. It will gain an equal amount of kinetic energy during each second.
    3. It will gain an equal amount of speed for each meter through which it falls.
    4. It will gain an equal amount of momentum for each meter through which it falls.
    5. The amount of momentum it gains will be proportional to the amount of potential energy that it loses.

 

2. A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large, air-filled bag. Which one of the following best describes why no injury occurs?

    1. The bag provides the necessary force to stop the person.
    2. The bag reduces the impulse to the person.
    3. The bag increases the amount of time the force acts on the person and reduces the change in momentum.
    4. The bag decreases the amount of time during which the momentum is changing and reduces the average force on the person.
    5. The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.

 

3. A 1.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. What is the change in momentum of the ball?

  1. zero kg • m/s                    (c) 12 kg • m/s, upward             (e) 24 kg • m/s, upward
  2. 12 kg • m/s, downward    (d) 24 kg • m/s, downward

 

4. A 0.065-kg tennis ball moving to the right with a speed of 15 m/s is struck by a tennis  racket, causing it to move to the left with a speed of 15 m/s. If the ball remains in  contact with the racquet for 0.020 s, what is the magnitude of the average force

experienced by the ball?

  1. zero newtons                       (c) 160 N                      (e) 9.8 104 N
  2. 98 N                                    (d) 1.6 105 N

 

5. While a car is stopped at a traffic light in a storm, raindrops strike the roof of the car. The area of he roof is 5.0 m2. Each raindrop has a mass of 3.7 10–4 kg and speed of 2.5 m/s before impact and is at rest after the impact. If, on average at a given time, 150 raindrops strike each square meter, what is the impulse of the rain striking the car?

  1. 0.69 N • s                 (c) 0.14 N • s                   (e) 21 N • s
  2. 0.046 N • s               (d) 11 N • s

 

6. A football player kicks a 0.41-kg football initially at rest; and the ball flies through the air. If the kicker’s foot was in contact with the ball for 0.051 s and the ball’s initial speed after the collision is 21 m/s, what was the magnitude of the average force on the football?

  1. 9.7 N                       (c) 81 N                 (e) 210 N
  2. 46 N                        (d) 170 N

 

 

A 4.0-kg block slides along a frictionless surface with a constant speed of 5.0 m/s. Two seconds after it begins sliding, a horizontal, time-dependent force is applied to the mass. The force is removed eight seconds later. The graph shows how the force on the block varies with time.

 

 

 

 

 

 

7.What is the magnitude of the total impulse of the force acting on the block?

    1. 20 N • s                       (c) 48 N • s                (e) 60 N • s  (b) 42 N • s                      (d) 54 N • s

 

8.What, approximately, is the speed of the block at t = 11 seconds?

    1. 5.0 m/s             (c) 25 m/s             (e) 75 m/s
    2. 16 m/s             (d) 65 m/s

 

 

9. A 50-kg toboggan is coasting on level snow. As it passes beneath a bridge, a 20-kg parcel is dropped straight down and lands in the toboggan. If (KE)1 is the original kinetic energy of the toboggan and (KE)2 is the kinetic energy after the parcel has been added, what is the ratio (KE)2/(KE)1.

    1. 0.4             (c) 0.7              (e) 1
    2. 0.6             (d) 0.8

 

10. An 80-kg astronaut carrying a 20-kg tool kit is initially drifting toward a stationary  space shuttle at a speed of 2 m/s. If she throws the tool kit toward the shuttle with a  speed of 6 m/s as seen from the shuttle, her final speed is

    1. 1 m/s toward the shuttle.                    (d) 4 m/s toward the shuttle.
    2. 1 m/s away from the shuttle.              (e) 6 m/s away from the shuttle.
    3. 2 m/s toward the shuttle.

 

11. Two objects of equal mass traveling toward each other with equal speeds undergo a head on collision. Which one of the following statements concerning their velocities after the collision is necessarily true?

    1. They will exchange velocities.                  (d) Their velocities will be zero.
    2. Their velocities will be reduced.               (e) Their velocities may be zero. (c) Their velocities will be unchanged.

 

12. Complete the following statement: Momentum will be conserved in a two-body collision only if

    1. both bodies come to rest.
    2. the collision is perfectly elastic.
    3. the kinetic energy of the system is conserved.
    4. the net external force acting on the two-body system is zero.
    5. the internal forces of the two body system cancel in action-reaction pairs.

 

 

 

The cart is  initially at rest.

 

 

 

 

 

13. If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart?

    1. 150 kg               (c) 210 kg             (e) 300 kg
    2. 175 kg               (d) 260 kg

 

14.  A 35-kg girl is standing near and to the left of a 43-kg boy on the frictionless surface of a frozen pond. The boy tosses a 0.75-kg ice ball to the girl with a horizontal speed of 6.2 m/s. What are the velocities of the boy and the girl immediately after the girl catches the ice ball?

girl                                         boy

    1. 0.81 m/s, left                0.67 m/s, right
    2. 0.17 m/s, left                0.14 m/s, left (c) 0.18 m/s, right              0.13 m/s, left
    1. 0.42 m/s, left                0.49 m/s, right
    2. 0.13 m/s, left                0.11 m/s, right

 

 

 

15. In the game of billiards, all the balls have approximately the same mass, about 0.17 kg. In the figure, the cue ball strikes another ball such that it follows the path shown. The other ball has a speed of 1.5 m/s immediately after the collision. What is the speed of the cue ball after the collision?

 

    1. 1.5 m/s      (c) 2.6 m/s       (e) 5.2 m/s
    2. 1.8 m/s        (d) 4.3 m/s

 

 

 

16. A 100-kg fisherman and a 500-kg supply crate are on a frozen pond that is essentially frictionless. The man and the crate are initially separated by a distance of 600 meters. The fisherman uses a very light rope to pull the crate closer to him. How far has the man moved when the crate reaches the fisherman?

(a) zero meters                     (c) 50 m             (e) 500 m (b) 10 m                               (d) 100 m

 

 

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