The momentum of a moving object is its mass multiplied by its velocity. The most convenient way to analyse the impact is to use the Principle of Conservation of Linear Momentum: the total momentum of both objects after the collision is equal to the total momentum before collision.
Two smooth spheres of masses m and 4m collide directly when moving in opposite directions with speeds u and v respectively. (See Fig. 1). The sphere of mass 4m is brought to rest by the impact. Prove that 
where e is the coefficient of restitution. (Note: masses are in kg, speeds are in m/s)
where e is the coefficient of restitution. (Note: masses are in kg, speeds are in m/s)
The next step is to identify the motion of the particles before and after the collision and express this in mathematical equations:
We have:
From the Principle of Conservation of Linear Momentum:
