Question

A machine with a mass of 4kg fires a 45g bullet at a speed of 100m/s...
What is the recoil speed of the machine gun

Answer 1

$M$ =4 kg - mass of machine

$m$ = 45 g - mass of bullet

$v$ = 100 m/s - speed of bullet

$v'$ - recoil speed of machine gun

Law of conservation of momentum:

$0=mv-Mv'$

Then $v'=mv/M=0.045*100/4=1.125$ m/s