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. The child now stretches his hands so that the moment of inertia of the system doubles. The kinetic energy of the system now is:

• A. 4K
• B. $K$
• C. $\frac{K}{2}$
• D. 2K

Answer 1

The correct option is C

$\frac{K}{2}$

By conservation of angular momentum ($I\omega$ =constant) angular velocity will become half.

Since $K=\frac{1}{2}I{\omega }^2$, the rotational kinetic energy will become half.