Question

Three point masses, each of mass are placed at the corners of an equilateral triangle of side l. Then the moment of inertia of this system about an axis along one side of the triangle is:

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

Answer 1

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

Apply parallel axis theorem. Two masses will be on axis of rotation. Another mass is away from the axis at a perpendicular distance of $lsin60$.