Question

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

• A. $\left(\sqrt{2}\right)I$
• B. $2I$
• C. $I/2$
• D. $I/\sqrt{2}$

Answer 1

Answer: (B)

Moment of inertia of thin uniform circular disc about one of its diameter is $I$
$\therefore I=\frac{M{R}^2}{4}\dots (i)$
where M is the mass and R is the radius of the disc. Moment of inertia of disc about an axis passing through the centre and perpendicular to the plane of the disc is $I$'
$I^{\prime }=\frac{M{R}^2}{2}=2\left(\frac{M{R}^2}{4}\right)=2I$ [Using $(i)]$