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**James S. Walker, Physics 4th edition, **** Addison-Wesley 2009**.

**Chapter 5
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1. An object of mass m is initially at rest. After a force of magnitude F acts on it for a time T, the object has a speed v. Suppose the mass of the object is doubled, and the magnitude of the force acting on it is quadrupled. In terms of T, how long does it take for the object to accelerate from rest to a speed v now?

2. On a planet far, far away, an astronaut picks up a rock. The rock has a mass of 5.00 kg, and on this particular planet its weight is 40.0 N. If the astronaut exerts an upward force of 46.2 N on the rock, what is its acceleration?

3. In a grocery store, you push a 12.3-kg shopping cart with a force of 10.1 N. If the cart starts at rest, how far does it move in 2.50 s?

4. You are pulling your little sister on her sled across an icy (frictionless) surface. When you exert a constant horizontal force of 120 N, the sled has an acceleration of 2.5 m/s2. If the sled has a mass of 7.4 kg, what is the mass of your little sister?

5. A 0.53-kg billiard ball initially at rest is given a speed of 12 m/s during a time interval of 4.0 ms. What average force acted on the ball during this time?

6. A 92-kg water skier floating in a lake is pulled from rest to a speed of 12 m/s in a distance of 25 m. What is the net force exerted on the skier, assuming his acceleration is constant?

7. You drop two balls of equal diameter from the same height at the same time. Ball 1 is made of metal and has a greater mass than ball 2, which is made of wood. The upward force due to air resistance is the same for both balls. (a) Is the drop time of ball 1 greater than, less than, or equal to the drop time of ball 2? (b) Choose the best explanation from among the following:

I. The acceleration of gravity is the same for all objects, regardless of mass.

II. The more massive ball is harder to accelerate.

III. Air resistance has less effect on the more massive ball.

8. A 42.0-kg parachutist is moving straight downward with a speed of 3.85 m/s. (a) If the parachutist comes to rest with constant acceleration over a distance of 0.750 m, what force does the ground exert on her? (b) If the parachutist comes to rest over a shorter distance, if the force exerted by the ground greater than, less than, or the same as in part (a)? Explain.

9. In baseball, a pitcher can accelerate a 0.15-kg ball from rest to 98 mi/h in a distance of a 1.7m. (a) What is the average force exerted on the ball during the pitch? (b) If the mass of the ball is increased, is the force required of the pitcher increased, decreased, or unchanged? Explain.

10. A major-league catcher gloves a 92-mi/h pitch and brings it to rest in 0.15 m. If the force exerted by the catcher is 803 N, what is the mass of the ball?

11. Driving home from school one day, you spot a ball rolling out into the street (Figure 5-18). You brake for 1.20 s, slowing your 950-kg car from 16.0 m/s to 9.50 m/s. (a) What was the average force exerted on your car during braking? (b) How far did you travel while braking?

12. Stopping a 747. A 747 jetliner lands and begins to slow to a stop as it moves along the runaway. If its mass is 3.50 × 105 kg, its speed is 27.0 m/s, and the net braking 4.30 × 105 N, (a) what is its speed 7.50 s later? (b) How far has it traveled in this time?

13. A drag racer crosses the finish line doing 202 mi/h and promptly deploys her drag chute (the small parachute used for braking). (a) What force must the drag chute exert on the 891-kg car to slow it to 45.0 mi/h in a distance of 185? (b) Describe the strategy you used to solve part (a).

14. A small car collides with a large truck. (a) Is the magnitude of the force experienced by the car greater than, less than, or equal to the magnitude of the force experienced by the truck? (b) Choose the best explanation from among the following:

I. Action-reaction forces always have equal magnitude.

II. The truck has more mass, and hence the force exerted on it is greater.

III. The massive truck exerts a greater force on the lightweight car.

15. A small car collides with a large truck. (a) Is the acceleration experienced by the car greater than, less than, or equal to the acceleration experienced by the truck? (b) Choose the best explanation from among the following:

I. The truck exerts a larger force on the car, giving it the greater acceleration.

II. Both vehicles experience the same magnitude of force, therefore the lightweight car experiences the greater acceleration.

III. The greater force exerted on the truck gives it the greater acceleration.

16. You hold a brick at rest in your hand. (a) How many forces act on the brick? (b) Identify these forces. (c) Are these forces equal and opposite in direction? (d) Are these forces an action-reaction pair? Explain.

17. Referring to Problem 16, you are now accelerating the brick upward. (a) How many forces act on the brick in this case? (b) Identify these forces. (c) Are these forces equal and opposite in direction? (d) Are these forces an action-reaction pair? Explain.

18. On vacation, your 1400-kg car pulls a 560-kg trailer away from a stoplight with an acceleration of 1.85 m/s2. (a) What is the net force exerted on the trailer? (b) What force does the trailer exert on the car? (c) What is the net force acting on the car?

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