Question

Two disc of same radius (r) and mass (m) are placed such that their centre is at a common point and their planes are perpendicular to each other. The moment of inertia of the system about an axis passing through the centre and perpendicular to plane of one of the discs is:

• A.
• B. mr²
• C.
• D. 2 mr²

Answer 1

The correct option is C

$I_1=m{r}^2/2$
$I_2=$moment of inertia about one of the diameters =$\frac{1}{4}m{r}^2\therefore I=I_1+I_2=\frac{3}{4}m{r}^2$