A bullet was fired from a stationary gun in a horizontal direction. The speed that the gun acquired is 10 cm / s

A bullet was fired from a stationary gun in a horizontal direction. The speed that the gun acquired is 10 cm / s, its weight is 5 kg, and the bullet speed is 400 m / s, determine the mass of the bullet

given:
v1 = 400m / s
m2 = 5 kg
v2 = 10m / s = 0.1m / s
find: m1
decision:
p1 = p2
p1 = m1 * v2
p2 = m2 * v2
m1 * v1 = m2 * v2
m1 = m2 * v2: v1 = 5 * 0.1: 400 = 0.00125 kg
Answer: 0.00125 kg bullet weight