a horizontal platform in the shape of a circular disk rotates in a horizontal plane about a frictionless vertical axle.the platform has a mass M=100 kg and a radius r=2.0 m.A student whose mass is m=60 kg walks slowly from the rim of the disk towards its center. If the angular speed of the system sis 2.0 rad/s when the student is at the rim, what is the angular speed when he has reached a point r=0.5 m from the center..

What do YOU think ?
While we're happy to help, we will NOt do all the work for you.

Think Conservation of angular momentum. Compute the moment of inertia of the system before and after the student walked toward the center.