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A man stands on a freely rotating platform, as shown, holding an exercise dumbbell in each...

A man stands on a freely rotating platform, as shown, holding an exercise dumbbell in each hand. With outstretched arms, his angular speed is 1.5 rad/s. After he has pulled his arms in, as shown, his angular speed is 5 rad/s. What is the ratio of his final rotational KE to his initial rotational KE? Explain any differences.

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Answer #1

the difference in the kinetic energy is due to the change in moment of inertia. As the person pulled his arms the radius of gyration decreases and hence they moment of inertia also decreases.

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