At what speed will the platform begin to rotate as the person moves from the platform edge to its center?

Question

A horizontal platform weighing 100 kg rotates about a vertical axis passing through the center of the platform at 10 rpm. The edge of the platform is occupied by a person weighing 588.6 N. At what speed will the platform begin to rotate as the person moves from the platform edge to its center? Consider the platform as a round, homogeneous disk, but a human as a point like body. [22 rpm].

Answer 1

This is about the conservation of angular momentum. L = m*v*r

m = mass

v = velocity

r = radius

If the platform is rotating, then the person walking towards the center has a decreasing value of L. This means that the rotation rate will increase. If the platform is not already moving, and the person walks directly towards the centerr, then there is no change in angular momentum---so the platform will no start rotating.

So- we need to know the initial rate of rotation in order to determine the effect of the person moving