Question

Two thin discs each of mass M and radius r metre are attached to form a rigid body as shown in figure. The rotational inertia of this body about an axis perpendicular to the plane of disc B and passing through its centre is :

• A. $2M{r}^2$
• B. $3M{r}^2$
• C. $4M{r}^2$
• D. $5M{r}^2$

Answer 1

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

Moment of inertia is denoted by I. It measures the extent to which an object resists the rotational acceleration, and it is the rotational analogue for mass.

For the spherical object with mass M and radius r , it will be computed as:

$I=I_B+I_A=\frac{1}{2}M{r}^2+(\frac{1}{2}M{r}^2+M{\left(2r\right)}^2)$

$I=5M{r}^2$

Thus option D is correct.