Question

A machine gun fires n bullets per sec with speed u and mass of each bullet is m .if bullet hit the wall and rebounds with the same speed ,then force acting on the wall is

Answer 1

Force is rate of change of momentum per second the n bullets hit the wall with velocity v and return at same velocity.

Therefore, change in momentum of 1 ball is { mv-m(-v)} =2mv.

So rate of change if momentum for n balls is 2mvn/1

Thus, force is 2nmv