A bullet weighing 10 g, flying horizontally, hit a box of sand with a total weight of 5 kg suspended

A bullet weighing 10 g, flying horizontally, hit a box of sand with a total weight of 5 kg suspended on a rope, and got stuck in it. At the same time, the box was pumped out, having risen by 10 cm. Determine the speed of the bullet before hitting.

mя = 5 kg.
mp = 0.01 kg.
h = 10 cm = 0.1 m.
g = 9.8 m / s ^ 2.
V -?
Let’s use the law of conservation of energy: (my + mp) * g * h = mp * V ^ 2/2, where my is the mass of the box with sand, mp is the mass of the bullet, V is the speed of the bullet. h – the height to which the box of sand has risen.
V = √ (2 * ((my + mp) * g * h) / mp).
V = √ (2 * ((5 kg + 0.01 kg) * 9.8 m / s ^ 2 * 0.1 m) / 0.01 kg) = 31 m / s.
Answer: V = 31 m / s.