Question

Three point masses, each of mass $m$, 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

Answer: (C)

$\frac{3}{4}m{l}^2$

$I_{AB}=0+0+m{\left(\frac{l\sqrt{3}}{2}\right)}^2$ where $I_{AB}$ is the MI about the side AB
$\therefore =\frac{3}{4}m{l}^2$