JEE Main Physics 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 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 . The boy now stretches his arms so as to hold the masses far from his body, and the moment of inertia of the system increases to . The kinetic energy of the system in the latter case as compared with that in the previous case will
Answer: (B)
Solution
With conserved, . Since doubles while stays fixed, is halved — it decreases.