Two particles having masses m1 and m2 are situated in a plane perpendicular to line AB at a distance of r1 and r2 respectively as shown. Find the moment of inertia about axis passing through centre of mass and perpendicular to line joining m1 and m2.
Centre of mass of system rcm = m2r1+r2m1+m2 = distance of centre of mass from m1
Distance of centre of mass from mass m2 = m1(r1+r2)(m1+m2)
So moment of inertia about its centre of mass = ICM = m1(m2(r1+r2)m1+m2)2+m2(m1(r1+r2)m1+m2)2
Icm = m1m2(r1+r2)2m1+m2