A circular plate is rotating in horizontal plane, about an axis… | JEE Main 2023 (11 Apr, Shift 2)

Q38JEE Main 2023 · 11 APR · SHIFT 2Medium

Angular Momentum & its Conservation

A circular plate is rotating in horizontal plane, about an axis passing through its center and perpendicular to the plate, with an angular velocity $\omega$ . A person sits at the center having two dumbbells in his hands. When he stretches out his hands, the moment of inertia of the system becomes triple. If E be the initial Kinetic energy of the system, then final Kinetic energy will be $\frac{E}{x}$ . The value of $x$ is

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Answer: 3

No external torque, so $L$ is constant and $K=\frac{L^2}{2I}$ .
$I\to3I \Rightarrow K\to\frac{E}{3}$
So $x=3$ .

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