This is conservation of angular momentum
Iiωi = Ifωf
Note: you must account for I of the platform (which will not change) plus I of the student (which changes as she goes from 3.21 to 1.23)
A horizontal circular platform (m = 110.1 kg, r = 3.21m) rotates about a frictionless vertical axle. A student (m = 98.3kg) walks slowly from the rim of the platform toward the center. The angular velocity, omega, of the system is 3.9 rad/s when the student is at the rim. Find omega when the student is 1.23m from the center.
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