# hmwk7 - 5 What quantities must be zero for equilibrium 6...

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Homework #7 Due midnight Sunday November 6. 1. In his discussion of the principle of conservation of momentum, what sport does Hay use as an example? 2. Give sports examples of a (nearly) elastic collision and of an inelastic collision. 3. A ping-pong ball hits the table with backspin. (a) Does a ping-pong ball have a low or high coeﬃcient of restitution? (b) Does a ping-pong ball have a low or high coeﬃcient of friction? (c) Is the velocity at the contact point larger or smaller than it would be if there was no spin? (d) Is the frictional force larger or smaller? (e) Is the horizontal component of the velocity larger or smaller after the bounce than it would be without topspin? (f) Is the angle of reﬂection larger or smaller? 4. What term does Hay use for “torque?” What is an athletic example Hay uses to explain the concept of torque?

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Unformatted text preview: 5. What quantities must be zero for equilibrium? 6. Mark each statement about the gymnast in the ﬁgure as True or False. Explain your reasoning. (a) The net torque is zero when she performs the stunt correctly. (b) The torque associated with her upper body tends to rotate her body clockwise. (c) The lever arm for the torque associated with her free leg is x 1 . (d) The torque produced by her free leg is larger in magnitude than the torque produced by her supporting leg. Warmup Questions Submit answers by 11:00 p.m. Monday November 7. 1. Warmup question for November 8. How does a ballerina manage to have her head ﬂoat at the same height for a long time when she performs a grand jete ? 2. Warmup question for November 3. Why does a ﬁgure skater spin faster when she pulls her arms in? 1 2...
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hmwk7 - 5 What quantities must be zero for equilibrium 6...

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