A physics student is sitting on a frictionless platform that is rotating with an angular speed of ωi = 1.0 rad/s. His arms are outstretched, and he is holding a heavy weight in each hand. The moment of inertia of the student, the extended weights, and the platform about the rotation axis is Ii = 8.1 kg·m2. When the student pulls the weights inward toward his body, the moment of inertia decreases to If = 4.5 kg·m2. What is the resulting angular speed, ωf, of the platform?

By how much is the kinetic energy of the system increased? (Think about where this increase in energy comes from!)