Q. 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 stretches his arms so that the moment of inertia of the system doubles. The kinetic energy of the system now is
A) $2K$
B) $\frac{K}{2}$
C) $\frac{K}{4}$
D) $4K$
Explanation
(b) From conservation of angular momentum ($I\omega$= constant), angular velocity will remain half. As,
$K = \frac{1}{2}I\omega^{2}$
The rotational kinetic energy will become half.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.