Question

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
decrease in 10 rad/s. If I is the initial moment of
inertia of the dancer, the new moment of inertia is
(a) 2I (b) 3I
(c) I/2 (d) I/3

Answer 1

Answer:

option a is correct.

Here, angular momentum is conserved.

Initial angular momentum = Final angular momentum

I×20=I′×10

where, I′ is the new moment of inertia.

Then,

I′=2I

Answer 2

Answer:

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

decrease in 10 rad/s. If I is the initial moment of

inertia of the dancer, the new moment of inertia is

(a) 2I ✔️✔️

(b) 3I

(c) I/2

(d) I/3