A physics student is sitting on a frictionlessplatform that is rotating with an

Question

A physics student is sitting on a frictionlessplatform that is rotating with an angular speed ofi = 1.3 rad/s. His arms areoutstretched, and he is holding a heavy weight in each hand. Themoment of inertia of the student, the extended weights, and theplatform about the rotation axis is Ii = 12.8kg·m2. When the student pullsthe weights inward toward his body, the moment of inertia decreasesto If = 5.6kg·m2.

What is the resulting angular speed, f, of theplatform?

By how much is the kinetic energy of thesystem increased? (Think about where this increase in energy comesfrom!)

Explanation / Answer

       From the conservation ofangular momentum                    Ii*i = If*f                    f= Ii*i / If                        = ---------- rad/s     The increase in kinetic energyis                K = (1/2)If*f2 -(1/2)Ii*i2                         = ------------ J      

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