Angular momentum/kinetic energy

[twituksh12345]

Homework Statement

An ice skater holds two weights in his outstretched hands and rotates about his vertical axis. Then he brings the weights closer to his hands.In accordance with the law of conservation of angular momentum,the angular velocity of the ice skater increases.But so does the rotational kinetic energy.Where does this extra energy come from?

Homework Equations

The Attempt at a Solution

 

[rl.bhat]

The muscles in his hands do work on the weights to bring them closer. this will increase the rotational kinetic energy.