A rifle of mass 2 kg is suspended by strings. The rifle fires a bullet of mass 0.01 kg at a speed of 200 m/s. The recoil velocity of the rifle is about

Question

Quizplus · Accepted Answer

The recoil velocity of the rifle can be calculated using the principle of conservation of momentum. Before firing, the total momentum of the system (rifle + bullet) is zero because neither is moving. After firing, the momentum of the bullet is $0.01 \, \text{kg} \times 200 \, \text{m/s} = 2 \, \text{kg} \cdot \text{m/s}$. To conserve momentum, the rifle must have an equal and opposite momentum. Since the mass of the rifle is $2 \, \text{kg}$, its recoil velocity $v$ can be found from $2 \, \text{kg} \cdot v = -2 \, \text{kg} \cdot \text{m/s}$, giving $v = -1 \, \text{m/s}$. The negative sign indicates direction opposite to the bullet's motion, but the magnitude of the velocity is $1 \, \text{m/s}$.

A Rifle of Mass 2 Kg Is Suspended by Strings