Q. If the external forces acting on a system have zero resultant, the center of mass
A) May move but not accelerate
B) May Accelerate
C) Must not move
D) None of the above
Explanation
(a) According to the equation of motion of the centre of mass
$M\ \mathbf{a}_{CM} = \mathbf{F}_{ext}$
If $\mathbf{F}_{ext} = 0,\ \mathbf{a}_{CM} = 0$
$\therefore$ $\mathbf{v}_{CM} = constant$
$ie$, if no external force acts on a system the velocity of its centre of mass remains constant. Thus, the centre of mass may move but not accelerate.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.