Two particles which are initially at rest, move towards each other under the action of their internal attraction. If their speeds are v and 2v at any instant, then the speed of centre of mass of the system will be:

Options

(a) 2v
(b) zero
(c) 1.5
(d) v

Correct Answer:

zero

Explanation:

If no external force actson a system of particles, the centre of mass remains as rest. So, speed of centre of mass is zero.