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NEET 2011 (AIPMT, Mains) · Angular Momentum & its Conservation

Angular Momentum & its Conservation question from NEET 2011 (AIPMT, Mains)

Q83NEET 2011 · AIPMT · MAINSEasy

Angular Momentum & its Conservation

A small mass attached to a string rotates on a frictionless table top as shown. If the tension in the string is increased by pulling the string causing the radius of the circular motion to decrease by a factor of 2, the kinetic energy of the mass will

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Answer: (d)

The pull is along the string (central), so $L = mvr$ is conserved.
$r \to r/2 \Rightarrow v \to 2v$
$KE = \tfrac{1}{2}mv^2 \to 4\,KE$ , so the answer is (d).

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