Q: A fly – wheel of mass 25kg has a radius of 0.2m. It is making 240 rpm. What is the torque necessary to bring to rest in 20 s ?

Sol: $\large \alpha = \frac{2\pi \nu}{t}$

$\large \alpha = \frac{2\pi \times 4}{20}$

Torque , $\large \tau = I \alpha $

$\large \tau = \frac{MR^2}{2} \alpha $

= 0.2π Nm