Question

Remya stands at the centre of a turn table with her two arms out stretched. The table is set rotating with an angular speed of 40 revolution/ minute . (a) what will happen to the moment of inertia if she folds her hands back ?(b) if the angular speed is increased to 100 rev/min, what will be the new moment of inertia ?​

Answer 1

Answer:

Since no external force acts on the boy, the angular momentum is constant.

Thus I1ω1=I2ω2

⟹ω2=I2I1ω1=25×40rev/min=100revmin

(b) Initial kinetic energy=E1=21I1ω12

Final kinetic energy=E2=21I2ω22

Thus E1E2=I1I2×ω12ω22=2.5

The increase in the rotational kinetic energy is attributed to the internal energy of the boy.