A disc of radius $2 ext{ m}$ and mass $100 ext{ kg}$ rolls on a horizontal floor. Its centre of mass has spe

Question

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

Accepted Answer

Work required = change in kinetic energy. Final KE = 0. Initial KE = $\frac{1}{2}mv^2 + \frac{1}{2}I\omega^2 = \frac{3}{4}mv^2 = \frac{3}{4} 	imes 100 	imes (20 	imes 10^{-2})^2 = 3	ext{ J}$. $|\Delta KE| = 3	ext{ J}$.

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