A ballet dancer, dancing on a smooth floor is spinning about a vertical axis with her arms folded with angular velocity of `20 rad//s`. When the stretches her arms fully, the spinning speed decrease in `10 rad//s`. If `I` is the initial moment of inertia of the dancer, the new moment of inertia is.

Options

A. 2I
B. 3I
C. `I/2`
D. `I/3`

Answer

A

Explanation

Here, angular momentum is conserved.
Initial angular momentum = Final angular momenum
`I xx 20 = I^(') xx 10`, where `I^(')` is new moment of inertia
`therefore I^(')=2I`