ism_ch05 - Chapter 5 Newton's Laws of Motion Answers to...

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82 Chapter 5 Newton’s Laws of Motion Answers to Even-numbered Conceptual Questions 2. As the dog shakes its body, it starts water in its fur moving in one direction. When it then begins to shake its body in the opposite direction, much of the water continues in the same direction – due to the law of inertia (Newton’s first law). As a result, water leaves the fur with each reversal in direction. 4. If the tablecloth is pulled rapidly, it can exert a force on the place settings for only a very short time. In this brief time, the objects on the table accelerate, but only slightly. Therefore, the objects may have barely moved by the time the tablecloth is completely removed. 6. The drag racer needs an engine to turn the wheels, which makes them push against the ground. It is only in this way that the ground is able to exert a reaction force on the car. 8. The astronaut should push the jet pack away from him, in the opposite direction from the spaceship. As a result, the reaction force exerted on him by the pack will accelerate him toward the ship. 10. The action-reaction forces are the force exerted on the ball by the bat, and the force exerted on the bat by the ball. The force exerted on the ball causes it to change its direction of motion and move into the field of play (hopefully). The force exerted on the bat slows its forward motion. 12. The forces between the two cars are an action-reaction pair; therefore, the forces have exactly the same magnitude. The effect of the forces is quite different, however. In particular, the car with the smaller mass experiences a greater acceleration than the car with the larger mass. This could increase the chance of injury for the occupants of the smaller car. 14. The floor exerts an upward force on the ball that causes it to rebound to your hand. 16. To cause a deceleration, the upward force exerted on you by the parachute must be greater in magnitude than your weight. In this case, the net force acting on you is upward, as is your acceleration. Since your acceleration and velocity are in different directions, you will decelerate. See Figure 2-11 for further details. 18. The whole brick also experiences twice the force due to gravity. As a result, these two effects (more inertia, more force) exactly cancel, and the free fall acceleration is independent of mass. 20. No. If only a single force acts on the object, it will not stay at rest; instead, it will accelerate in the direction of the force. 22. Object 1 has the greater net force acting on it, due to its larger mass. Therefore, object 1 reaches the ground first. 24. Yes. In the upwardly accelerating elevator it is as if you are playing a game of darts on a planet with a greater acceleration of gravity. Therefore, you must aim higher than you would if the elevator were moving upward with constant speed.
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Physics: An Introduction Chapter 5: Newton’s Laws of Motion 26. (a) When the parrot jumps, it pushes down on its perch. In this case, the scale reads a larger value. (b) When the parrot is in the air, the scale reads only the weight of the bird cage.
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ism_ch05 - Chapter 5 Newton's Laws of Motion Answers to...

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