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

Options

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

Answer

A

Explanation

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