Question

A bullet is fired from a rifle which recoils after firing. The ratio of kinetic energy of the rifle to that of the bullet is –

Q: Answer-A bullet is fired from a rifle which recoils after firing. The ratio of kinetic energy of the rifle...

The rifle and bullet have zero momentum and zero kinetic energy to start with. When the trigger is pulled, the bullet gains some momentum in the forward direction, but this is canceled by the rifles backward momentum, so the total momentum is still zero. The kinetic energies of the gun and bullet are both positive scalars, however, and do not cancel.