A person with mass mp = 77 kg stands on a spinning platform disk with a radius of R = 2.16 m and mass md = 185 kg. The disk is initially spinning at ? = 1.6 rad/s. The person then walks 2/3 of the way toward the center of the disk (ending 0.72 m from the center).
1. What is the change in the total kinetic energy of the person and disk? (A positive value means the energy increased.)
2. If the person now walks back to the rim of the disk, what is the final angular speed of the disk?