A man standing on a platform holds weights in his outstretched arms. The system rotates freely about a central vertical axis. If he now draws the weights inwards close to his body,

the angular velocity of the system will increase.

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the angular momentum of the system will decrease.

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the kinetic energy of the system will increase.

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he will have to expend some energy to draw the weights in.

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Solution

The correct options are
A the angular velocity of the system will increase.
C he will have to expend some energy to draw the weights in.
D the kinetic energy of the system will increase.
When the person contracts his hands he is decreasing his moment of inertia thereby increasing his angular velocity using the principle of conservation of angular momentum $I_{1} ω_{1} = I_{2} ω_{2}$
As the angular velocity increases, its kinetic energy also increases. Also energy would be required to draw the weights inwards from its position.

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