Rotational Motion question bank (Physics)

Moment of inertia of a disc about its own axis is I. Its moment of inertia about a tangential axis in its plane is

A solid disc of radius $40\ \text{cm}$ and the mass of $20\ \text{kg}$ is rotating with an angular velocity of $300\ \text{rpm}$, about an axis passing through its centre of mass and perpendicular to its plane. The magnitude of retarding torque required to bring the disc at rest in $20\ \text{s}$ is $x\pi\ \text{Nm}$. The value of $x$ is