Question

A metallic ring of mass 1 kg has moment of inertia 1 kg m when rotating about one of its diameters. It is molten and remoulded into a thin uniform disc of the same radius. How much will its moment of inertia be, when rotated about its own axis.

Answer 1

The MI of the thin ring about its diameter, I_ring = 1/2 MR² = 1Kg.m²

Since the ring is melted and recast into a thin disc of same radius R, the mass of the disc equals the mass of the ring = M.

The MI of the thin disc about its own axis (i.e., transverse symmetry axis) is