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The speed of rotation of a person with s...

The speed of rotation of a person with some weights in his hands and standing on a rotating platform increases as he draws his arms close to his chest.Why?Explain.

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A man stands on a rotating platform, with his arms stretched horizontally holding a 5 kg 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 90cm to 20cm. 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 :- Is kinetic energy conserved in the process? If not, from where does the change come about?

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JBD PUBLICATION-MOTION OF SYSTEM OF PARTICLES AND RIGID BODY-EXAMPLE
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  2. What is law of conservation of momentum ?

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