Question

Three point masses, each of mass m are placed at the cornets of an equilateral triangle of side a. The moment of inertia of this system about, an axis along one side of the triangle is

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

Answer 1

The correct option is C $\frac{3}{4}m{a}^2$

The moment of inertia of two masses which lies on the axis will be zero.

Altitude in equilateral triangle is $h=a\frac{\sqrt{3}}{2}$

$I=m{h}^2=\frac{3m{a}^2}{4}$