\(\omega = 25 \times 2\pi \,rad/5\)
\( = 50\,\,\pi \,\,rad/\sec \)
\(\omega = \frac{\tau }{I}t\)
\(\tau = \frac{{I\omega }}{t} = \frac{{5m{r^2}}}{4} \times \frac{\omega }{t}\)
\( = \frac{{5 \times 5 \times {{10}^{ - 3}} \times {{10}^{ - 4}} \times 50\,\pi }}{{4 \times 5}}\)
\( = \frac{{25\pi }}{4} \times {10^{ - 6}} = 2 \times {10^{ - 5}}\)