Velocity of centre of mass of a system,
\(\vec{v}_{CM}=\frac{d\vec{r}}{dt}\)
Total external force
\(\vec{F}=M\frac{d^2\vec{r}}{dt^2}\)
\(=M\frac{d\vec{v}_{cm}}{dt}........(1)\)
Internal force cancel out in pairs, so velocity of centre of mass is not affected by internal force.
Putting \(\vec{F}\) = 0 in equation (i),
\(=M\frac{d\vec{v}_{cm}}{dt} =0\) ( m ≠ 0)
i.e.,, \(\vec{v}_{CM}\) =constant
If resultant external forces is zero, the velocity of centre of mass remains same.
