A disc of radius 2 m and mass 100 kg rolls on a horizontal floor. Its centre of mass has speed of 20 cm/s. How much work is needed to stop it ?

1. 3 J

2. 30 kJ

3. 2 J

4. 1 J

Doubtly Asked 30 Oct 2026 NEET UG 2019 Practice test neet Save WhatsApp Report

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Answer: 1. 3 J

To stop the disc we must remove its total kinetic energy, which is translational plus rotational.

\(K=\tfrac12mv^2+\tfrac12I\omega^2\) with \(I=\tfrac12mR^2\) and \(\omega=v/R\) (rolling), so \(K=\tfrac34mv^2\).

\(K=\tfrac34\times100\times(0.2)^2=3\) J.

Work needed \(=3\) J (the radius is not needed).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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