Give short answer for the following question:
 
Prove the law involved in the rocket propulsion with given consideration.

Consider two bodies, A and B, having masses \(m_1\) and \(m_2\), move with an initial velocity \(u_1\) and \(u_2\) in a straight line.   Let the initial velocity of the body, A be higher than that of the body, B. i.e., \({u_1} > {u_2}\).   During a period of time \(t\) \(second\), they tend to have a collision. After the impact, both bodies move along the same straight line with a velocity \(v_1\) and \(v_2\), respectively.
 
Statement:
 
There is  of bodies as long as  acts on them.
 
Force on body B due to A,