Radius of hoop, $R = 2\,\text{m}$Mass of hoop, $M = 100\,\text{kg}$Velocity of centre of mass $= 20\,\text{cm}\,\text{s}^{-1} = 0.2\,\text{m}\,\text{s}^{-1}$The total kinetic energy of the hoop$= \frac{1}{2} M v^{2} + \frac{1}{2} I \omega^{2}$$= \frac{1}{2} M v^{2} + \frac{1}{2} M R^{2} \omega^{2}$$= \frac{1}{2} M v^{2} + \frac{1}{2} M R^{2} \omega^{2}$$= \frac{1}{2} M v^{2} + \frac{1}{2} M v^{2}$$= M v^{2} = 100 \times (0.2)^{2} = 4\,\text{J}$By work-energy theorem,Work required to stop the hoop = Total kinetic energy of hoop = 4 J