A boy stands over the center of a horizontal platform which is rotating freely with a speed of $$2$$ revolutions per second about a vertical axis through the center 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 x $$metre2$$. The boy now stretches his arms so as to hold the masses far from his body. In this situation, the moment of inertia of the system increases to $$2$$ kg x $$metre2$$. The kinetic energy of the system in the latter case as compared with that in the previous case will

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Infinity Learn · Accepted Answer

Since, external torque on system is zero, angular momentum is conserved.$$L=I$$ωSo, if I is doubled. ω is halvedNow, Rotational K.E.$$=L22IClearly$$, rotational $$KE$$  decreases (becomes$$ $$half).

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