Question

A machine gun fires n bullets per second each of mass m. If the speed of each bullet is v, then the force of recoil is?

Answer 1

Since, the momentum of gun and bullet together was zero before firing, so, after firing:
momentum of bullets+momentum of gun=0
momentum of the gun=-momentum of the bullets
momentum of bullet for each fire=mu
since, n bullets are fired per second.
Change in momentum of bullet per second=nmu
Therefore, change in momentum of gun per second is =-nmu[since direction of gun and bullet are opposite]
since, Force=rate of change of momentum
Force on gun= -nmu
Therefore Force of recoil is=nmu.
The force is directed opposite to the direction of the bullets.