Question

If the external force acting on a system have zero resultant, the centre of mass
(a) must not move
(b) must not accelerate
(c) may move
(d) may accelerate.

Answer 1

(b) must not accelerate
(c) may move

If the external force acting on a system has zero resultant,
then, acceleration of centre of mass \[= \frac{\vec{F}_{net}}{M} = 0\]
However, it may move uniformly with constant velocity.