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NEET 2015 (AIPMT, Cancelled Paper) · Angular Momentum & its Conservation

Angular Momentum & its Conservation question from NEET 2015 (AIPMT, Cancelled Paper)

Q73NEET 2015 · AIPMT · CANCELLED PAPERMedium

Angular Momentum & its Conservation

A mass m moves in a circle on a smooth horizontal plane with velocity v0 at a radius R0. The mass is attached to a string which passes through a smooth hole in the plane as shown. the tension in the string is increased gradually and finally m moves in a circle of radius $\frac{R_0}{2}$ .

The final value of the kinetic energy is

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Answer: (a)

Tension passes through the hole, so torque about it is zero and $mvR$ is conserved.
$mv_0R_0=mv\frac{R_0}{2}\Rightarrow v=2v_0$
$K=\frac12m(2v_0)^2=2mv_0^2$
So the answer is (a) $2mv_0^2$ .

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