Question
Discuss the motion of center of mass of a system consisting of n particles and show that center of mass moves with constant velocity in the absence of external force.
Solution
Consider a system of n particles of masses m1, m2, ..... mn having position vectors 
. The position of the centre of mass of the system is, 
If M is the total mass of the system, then 
are the net forces (internal + external) acting on masses m1, m2 ..... and mn respectively.
The net force on the system of particles is, 
