A solid disc of radius 20cm and mass 10kg is rotating with an...

$τ = \dfrac{\DeltaL}{\Deltat} = \dfrac{I\left({\omega}_{f} - {\omega}_{i}\right)}{\Deltat}$

$τ = \dfrac{\dfrac{m{R}^{2}}{2} \times [ 0 - \omega ]}{\Deltat}$

$= \dfrac{10 \times {\left(20 \times {10}^{- 2}\right)}^{2}}{2} \times \dfrac{600 \times \pi}{30 \times 10}$

$= 0 . 4\pi = 4\pi \times {10}^{- 1}$