Moment of inertia of a body about an axis is $4\;kgm^2$. The body is initially at rest and a torque of $8\;Nm$ starts acting on it along the same axis. Work done by the torque in $20\;sec.$ in joules, is

Question

\[(a)\;40 \quad (b)\;640 \quad (c)\;2560 \quad (d)\;3200 \]