Chapter 11, Problem 90AP

A boy stands at the center of a platform that is rotating without friction at 1.0 rev/s. The boy holds weights as far from his body as possible. At this position the total moment of inertia of the boy, platform, and weights is $5.0\text{kg}\cdot {\text{m}}^{\text{2}}$ . The boy draws the weights in close to his body, thereby decreasing the total moment of inertia to $1.5\text{kg}\cdot {\text{m}}^{\text{2}}$ . (a) What Is the final angular velocity of the platform? (b) By how much does the rotational kinetic energy increase?