# What is the recoil velocity of a rifle, stationary when fired, if the mass of the rifle is 4 kg

January 31, 2021 | education

| **What is the recoil velocity of a rifle, stationary when fired, if the mass of the rifle is 4 kg, the mass of the bullet is 8 g, and the velocity of the bullet is 600 m / s?**

m1 = 4 kilograms is the mass of the rifle;

m2 = 8 grams = 0.008 kilograms – bullet weight;

v2 = 600 meters per second – bullet speed.

It is required to determine the speed of the rifle at recoil v1 (meter per second).

Since, according to the condition of the problem, the rifle is stationary when fired, which, according to the law of conservation of momentum (momentum):

m1 * v1 = m2 * v2, hence:

v1 = m2 * v2 / m1 = 0.008 * 600/4 = 4.8 / 4 = 1.2 meters per second.

Answer: The recoil speed of the rifle is 1.2 meters per second.

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