Consider a light rod with two heavy mass particles at its ends. Let AB be a line perpendicular to the rod as shown in figure. What is the moment of inertia of the system about AB?

Explanation

Moment of inertia of the particle on the left is `m_1r_1^2`
Moment of inertia of the particle on the right is `m_2r_2^2`. Moment of inertia of the rod is negligible as the rod is light.
Thus the moment of inertia of the system about AB is
`m_1r_1^2+m_2r_2^2`