A circular metal disc of mass `200g` and radius `20cm` makes `10` revolutions per second about an axis passing through the centre and perpendicular to its plane. Find a) Moment of inertia about to axis, b) Torque required to change its angular velocity from `10` rps to `20` rps in `5s`.

Explanation

`(a) I=(Mr^(2))/(2)=(0.2xx(0.2)^(2))/(2)=4xx10^(-3)kgm^(2)`
(b) Torque `tau=Ialpha=(I(omega_(2)-omega_(1)))/(t)`
`:.tau=(4xx10^(-3)(40pi-20pi))/(5)`, `tau=0.05Nm`