Question

The moment of inertia of a disc of mass m and radius R about an axis, which is tangential the circumference of the disc and parallel to the diameter is?

• A. $\frac{3}{2}m{R}^2$
• B. $\frac{2}{3}m{R}^2$
• C. $\frac{5}{4}m{R}^2$
• D. $\frac{4}{5}m{R}^2$

Answer 1

The correct option is C $\frac{5}{4}m{R}^2$

Use parallel axis theorem, from the theorem of parallel axis, the moment of inertia(l) of a body about given axis is equal to its moment of inertia l about its diameter, plus the product of the mass M of the body and square of perpendicular distance between the two axes. That is
$l=l_d+M{R}^2=\frac{1}{2}M{R}^2+M{R}^2=\frac{5}{4}M{R}^2$.