A boy stands over the centre of a horizontal platform which is rotating freely with a speed of $2\ revolutions/sec$ about a vertical axis through the centre of the platform and straight up through the boy. He holds $2\ kg$ masses in each of his hands close to his body. The combined moment of inertia of the system is $1\ kg imes metre^{2}$. The boy now stretches his arms so as to hold the masses of inertia of the system increases to $2\ kg\ imes metre^{2}$. The kinetic energy of the system in the latter case as compared with that in the previous case will

Question

A boy stands over the centre of a horizontal platform which is rotating freely with a speed of $2\ revolutions/sec$ about a vertical axis through the centre of the platform and straight up through the boy. He holds $2\ kg$ masses in each of his hands close to his body. The combined moment of inertia of the system is $1\ kg 	imes metre^{2}$. The boy now stretches his arms so as to hold the masses of inertia of the system increases to $2\ kg\ 	imes metre^{2}$. The kinetic energy of the system in the latter case as compared with that in the previous case will

Dr. Abubacker · Accepted Answer

(b) $E = \frac{L^{2}}{2I}$. If boy stretches his arm then moment of inertia increases and accordingly kinetic energy of the system decreases because $L =$ constant and $E \propto \frac{1}{I}$

Explanation

Reviewed by Dr. Abubacker

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