A man stands on a frictionless platform that is rotating with an angular speed of 1.5 rev/s. His arms are outstretched, and he holds a heavy weight in each hand. The moment of inertia of the man, the extended weights, and the platform is 6 kg ∙ m2. When the man pulls the weights inward toward his body, the moment of inertia decreases to 1.8 kg ∙ m2.

(a) What is the resulting angular speed of the platform?

(b) What is the change in kinetic energy of the system?

(c) Where did this increase in energy come from?