Question

Two particles A and B, initially at rest, start moving towards each other under a mutual force of attraction. When the speed of A is “10 m/s” and the speed of B is “800 m/s”, what is the speed of their centre of mass?

(a) 0

(b) 0.8v

(c) 80v

(d) 8v

This question was posed to me in semester exam.

Question is taken from System of Particles topic in section System of Particles and Rotational Motion of Physics – Class 11

Answer 1

The correct answer is (a) 0

The explanation: Since both A and B are moving towards each other due to mutual force of attraction, we can infer that the particles of the system are in motion due to internal forces and hence the state of centre of mass will remain unchanged, i.e., at rest.