A horizontal platform in the shape of a circular disk rotates on a frictionless

Question

A horizontal platform in the shape of a circular disk rotates on a frictionless bearing about a vertical axle through the center of the disk. The platform has a mass of 150kg, a radius of 2.0m, and a rotational inertia of 300kgxm2 about the axis of rotation. A 60 kg student walks slowly from the rim of the platform toward the center.

If the angular speed of the system is 1.5 rad/s when the student starts at the rim, what is the angular speed when she is 0.50 m from the center?

Please, can you explain in detail how to factor in the fact that she is .50m from the center?

Explanation / Answer

conserving angular momentum
I11=I22

2=I11/I2

I1=300+60*2^2(inertia of disk+man wrt to disk=mr^2)

I2=300+60*0.5^2

1=1.5

2=(300+240)*1.5/(300+15)

=2.57 rad/s

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