Question

If net force acting on system of particles is zero, choose an incorrect option regarding the motion of the centre of mass of the system.

• A. Acceleration of COM will always be zero.
• B. Velocity of COM will always be zero.
• C. Both (a) and (b)
• D. None of these

Answer 1

The correct option is B Velocity of COM will always be zero.

We know that,
$F_{\text{net}}=0$
$\Rightarrow a_{\text{COM}}=0$
If $a_{\text{COM}}$ is zero then $v_{\text{COM}}$ will remain constant.
$v_{\text{COM}}$ may remain zero if initially $v_{\text{COM}}$ is at rest but not necessarily always. (Newton's $1$st law)
$\therefore$ Option (b) is correct.