posted by Anon .
A girl holds a 1.7 kg air rifle loosely and fires a bullet of mass 2 g. The muzzle velocity of the bullet is 160 m/s. What is the magnitude of the recoil velocity of the gun?
Since total momentum is conserved (and remains zero) the forward mometum of the bullet equals the the momentum of the gun in the opposite direction.
Holding the rifle tightly will diminish the recoil velocity, by applying an outside force. That is why the word "loosely" was added to the question.