Question

Two discs $A$ and $B$ of same mass $M$ and radius $R$ are connected to one another to form a single rigid body. Moment of inertia of this attachment about an axis normal to the plane of disc $A$ and passing through its centre is

• A. $2M{R}^2$
• B. $3M{R}^2$
• C. $\left(3/2\right)M{R}^2$
• D. $5M{R}^2$

Answer 1

The correct option is D $5M{R}^2$

The moment of inertia of the disc is given as $\frac{1}{2}M{R}^2$. For the second disc attached the moment of inertia would be $\frac{1}{2}M{R}^2+M(2R{)}^2$. Thus we get the total moment of inertia as $5M{R}^2$