Question

Two particles A and B, initially at rest, moves towards each other under a mutual force of attraction. At the instant when the speed of A is v and the speed of B is 2 v, the speed of centre of mass is(a) zero(b) v(c) 1.5 v(d) 3 v

Answer 1

Answer:

A) Zero

Explanation:

Particles = 2 = A and B (Given)

Speed of A = v (Given)

Speed of B = 2v (Given)

The two particles A and B are at a rest, thus the momentum of centre of mass is 0. = Pi=0

And no external force act on the system so,  Pi=Pf

Thus, there will be no change in the momentum of centre of mass and it will also remain zero. As the momentum(product of mass and velocity) is zero the velocity must also be zero. Thus, At the instant when the speed of A is v and the speed of B is 2 v, the speed of centre of mass is zero.