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in Physics by (50.3k points)

A man spinning in free space can change the moment of inertia of his body (I) by changing its shape. In this process, 

(a) he will have to expend some energy to increase I 

(b) he will have to expend some energy to decrease I 

(c) he does not have to expend any energy to change I 

(d) either (a) or (b) depending on the initial value of I 

1 Answer

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by (51.1k points)
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Best answer

Correct Answer is: (b) he will have to expend some energy to decrease I

Let L = angular momentum ω = angular velocity 

I = moment of inertia.

Here, L is conserved. ∴ L = Iω = constant.

Kinetic energy =E = 1/2 Iω2 = 1/2 .I (L/I)2 = L2/2I

If I decreases, E increases. Hence, energy must be expended.

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