Question

The bullet from a soldier's rifle has mass of 0.03kg. When the rifle is fired, the bullet leaves therifle with a velocity of 350 m/s. if the mass of the rifle is 5 kg. What is the velocity with which therifle recoils?​

Answer 1

According to conservation of momentum:

$$p_i=p_f,\\ mv=Mu,\\\space\\ u=v\frac mM=350\frac{0.03}{5}=2.1\text{ m/s}.$$