Question

From a circular disc of radius R and mass 9M, a small disc of mass M and radius R/3 removed concentrically. The moment of inertia of the remaining disc about an axis perpendicular to the plane of the disc and passing through its centre is

(a) 40/9 MR²

(b) MR²

(c) 4 MR²

(d) 4/9 MR²

Answer 1

Correct option (a) 40/9 MR²

Explanation:

Mass of the disc = 9M Mass of removed portion of disc = M The moment oi inertia of the complete disc about an axis passing through its centre O and perpendicular to its plane is I₁= 9/2 MR²

Now, the moment of inertia of the disc with removed portion

There, moment of inertia of the remaing portion of disc about o is