Question

Show that in the absence of an external force centre of mass moves become with a constant velocity

Answer 1

M for mass 

And v for velocity  

When there is not external force the acceleration of body is zero 

The velocity of the body will be 'v' 

Force = rate of change of momentum 

=> F = d(mv)/dt 

=> m (dv/dt) = F 

The external force F = 0 

M(dv/dt) = 0 

Dv/dt = 0 

M is not zero 

So this proves that velocity will always be constant in such scenario