Question

A uniform disc of radius R has a round disc of radius R/3 cut as shown in Fig. The mass of the remaining (shaded) portion of the disc equals M. Find the moment of inertia of such a disc relative to the axis passing through geometrical centre of original disc and perpendicular to the plane of the disc.

Answer 1

Let the mass per unit area of the material of disc be σ . Now the empty space can be considered as having density – σ and σ .