Sol. Using work energy theorem $$ \begin{aligned} & \mathrm{W}=\Delta \mathrm{KE}=0-\left(\frac{1}{2} \mathrm{mv}^2+\frac{1}{2} \mathrm{I} \omega^2\right) \\ & \mathrm{W}=0-\frac{1}{2} \mathrm{mv}^2\left(1+\frac{\mathrm{K}^2}{\mathrm{R}^2}\right) \\ & =-\frac{1}{2} \times 50 \times 0.4^2\left(1+\frac{1}{2}\right)=-6 \mathrm{~J} \end{aligned} $$ Absolute work $=+6 \mathrm{~J}$ $$ \mathrm{W}=-6 \mathrm{~J}|\mathrm{~W}|=6 \mathrm{~J} $$