The motion of the centre of mass of a system of two particles is unaffected by their internal forces.

Options

A. irrespective of the actual direction of the internal forces.
B. only if they are along the line joining the particles
C. only if they are at right angles to the joining the particles
D. only if they are obliquely inclined to the line joining the particle.

Answer

A

Explanation

(b) Only in this case, the total effect of internal forces can be cancelled.