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

Options

A. 2 K
B. `(K)/(2)`
C. `(K)/(4)`
D. 4 K

Answer

B

Explanation

According to the principle of conservation of angular momentum , `I omega `= constant
As I is doubled , `omega` becomes half
Now KE of rotation , `K = (1)/(2) I omega^(2)`
Since I is doulbed and `omega` is halved , KE will become half i.e., `(K)/(2)`