• # question_answer If the external forces acting on a system have zero resultant, the centre of mass A)  may move but not accelerate B)  may accelerate C)  must not move D)  None of die above

According to the equation of motion of the centre of mass $M{{\vec{a}}_{CM}}={{\vec{F}}_{ext}}$                 If ${{\vec{F}}_{ext}}=0,{{\vec{a}}_{CM}}=0$                 $\therefore$  ${{\vec{v}}_{CM}}=\text{constant}$ 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.