Question

Consider a system on which there are external forces acting. If the vector sum of all these external forces is zero, then the centre of mass _____

(a) must not move

(b) may move

(c) may accelerate

(d) must accelerate

I had been asked this question during an interview.

Asked question is from System of Particles in section System of Particles and Rotational Motion of Physics – Class 11

Answer 1

The correct choice is (b) may move

To explain: Since the vector addition of all external forces is zero, we know that the acceleration vector is zero for the resultant force vector as mass cannot be zero. Zero acceleration can imply zero or non-zero constant velocity. Thus, the centre of mass may move.