Question

A child is standing with folded hands at the centre of a platform rotating about its central axis. The kinetic energy of the system is K. Now, the child stretches his arms so that moment of inertia of the system doubled. Now, the kinetic energy of the system is

• A.
• B.
• C. 2K
• D. 4K

Answer 1

Answer: (B)

Answer 2

Initial kinetic energy, ..(i)

According to the principle of conservation of angular momentum, I$\omega$= constant As I is doubled, $\omega$becomes half.

So final kinetic energy.

(Using (i))