Q. From a disc of radius $R$, a concentric circular portion of radius $r$ is cut out so as to leave an annular disc of mass $M$. The moment of inertia of this annular disc about the axis perpendicular to its plane and passing through its centre of gravity is
A) $\frac{1}{2}\ M\ \left( R^{2\ } + r^{2} \right)$
B) $\frac{1}{2}M\left( R^{2\ } - r^{2} \right)$
C) $\frac{1}{2}M\left( R^{4\ } + r^{4} \right)$
D) $\frac{1}{2}M'\left( R^{4\ } - r^{4} \right)$
Explanation
(a) The moment of inertia of this annular disc about the axis perpendicular to its plane will be $\frac{1}{2}M(R^{2} + r^{2})$.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.