Question

The moment of inertia of a thin uniform circular disc about one of the diameters is $I$. Its moment of inertia about an axis perpendicular to the circular surface and passing through its centre is :

• A. $\sqrt{2}I$
• B. $2I$
• C. $\frac{I}{2}$
• D. $\frac{I}{\sqrt{2}}$

Answer 1

The correct option is B $2I$

The moment of inertia about any diameter is $I$.
The moment of inertia about another diameter which is inclined at ${90}^o$ to the first one is also $I$.
Thus using perpendicular axis theorem ($I_x+I_y=I_z$) the moment of inertia about the axis passing through the center and perpendicular to the plane would be
$I+I=2I$