Angular Momentum and Rotational Energy. A figure skater stands on one spot on th

Question

Angular Momentum and Rotational Energy. A figure skater stands on one spot on the ice (assumed frictionless) and spins around with her arms extended. When she pulls in her arms, she reduces her moment of inertia about the spin axis passing through her center of mass and her angular speed increases so that her angular momentum is conserved. Compared to her initial rotational kinetic energy, her rotational kinetic energy after she has pulled in her arms must be 1. the same. 2. larger because she's rotating faster 3. smaller because her moment of inertia is smaller. Explain your reasoning.

Explanation / Answer

When she pull in her arms , Her moment of inertia is reduced , but as angular momentum is conserved, angular speed of the skater increases !!!

Now Rotational kinetic energy is given by,
K.Erot = 1/2 * I * w^2
As the angular speed of the skater increases, Rotational kinetic energy also increases !!!

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