Question

Two particles A and B, initially at rest, move towards each other under mutual force of attraction. At the instant when the speed of A is v and the speed of B is 2v, what is the speed of mass of the system?

(a) 3v

(b) v

(c) Zero

(d) 1.5v

The question was posed to me in a national level competition.

I'm obligated to ask this question of Angular Momentum in division System of Particles and Rotational Motion of Engineering Physics I

Answer 1

Correct answer is (c) Zero

To explain: No external force is acting on the centre of mass. It remains at rest. The speed of centre of mass is zero.