When fired, a bullet weighing 10 g flew out of the rifle barrel at a speed of 840 m / s.

When fired, a bullet weighing 10 g flew out of the rifle barrel at a speed of 840 m / s. Determine the mass of the rifle if its recoil speed is 2 m / s.

These tasks: mp (the mass of the bullet ejected from the rifle barrel) = 10 g (in SI mp = 0.01 kg); Vp (bullet exit speed) = 840 m / s; Vv (rifle recoil speed) = 2 m / s.

To determine the mass of the rifle, we use the equality (we use the law of conservation of momentum): mp * Vp = mw * Vw, whence mw = mp * Vp / Vw.

Let’s calculate: mw = 0.01 * 840/2 = 4.2 kg.

Answer: The rifle has a mass of 4.2 kg.