Q 7.23    A man stands on a rotating platform, with his arms stretched horizontally holding a               $5kg$  weight in each hand. The angular speed of the platform is $30$ revolutions per               minute. The man then brings his arms close to his body with the distance of each               weight from the axis changing from $90 cm$ to $20 cm$. The moment of inertia of the               man together with the platform may be taken to be constant and equal to $7.6 kg m^{2}$.              (b) Is kinetic energy conserved in the process? If not, from where does the change come about?

No, the kinetic is not constant. The kinetic energy increases with decrease in moment of inertia. The work done by man in folding and stretching hands is responsible for this result.

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