What is the equation of the moment of inertia of a disc about an axis passing through its center and measured perpendicular to its plane?

Moment of inertia plays the same roll in rotational motion as mass in linear motion. The moment of inertia of a body changes when the axis of rotation changes.If the moment of inertia of a disc about an axis passing through its centre and perpendicular to its plane is (MR^2)/2) ( M is the mass of the disc and R its radius). Determine its moment of inertia about a diameter and about a tangent.

What is the radius of gyration of the ring about an axis passing through its centre mass and perpendicular to its plane?

Two identical concentric rings each of mass M and radius R are placed perpendicular to each other. What is the moment of inertia about an axis passing through the center of this system and perpendicular to the plane of one of the rings?