# A bullet weighing 10 g flew out of machine gun 3 at a speed of 700 m / s. As a result of the rebound

A bullet weighing 10 g flew out of machine gun 3 at a speed of 700 m / s. As a result of the rebound, the assault rifle acquired a speed of 1.6 m / s. What is the mass of the machine?

We calculate the mass of the automaton using the law of conservation of momentum:

(m1 + m2) * V1.2 = m1V1 + m2V2, where m1 is the mass of the bullet (m1 = 10 g or 0.01 kg), m2 is the desired mass of the assault rifle, V1.2 is the initial velocity of the bullet and the assault rifle (V1.2 = 0 m / s), V1 is the speed of the bullet after the shot (V1 = 700 m / s), V2 is the speed of the machine gun after the shot (V2 = 1.6 m / s).

0 = m1V1 + m2V2.

| m1V1 | = | m2V2 |.

m2 = m1V1 / V2.

Let’s perform the calculation:

m2 = 0.01 * 700 / 1.6 = 4.375 kg.

Answer: The mass of the machine is 4.375 kg.

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