# The spacecraft with a total mass of 2 tons shoots off the spent degree. The mass of the degree is 200 kg

**The spacecraft with a total mass of 2 tons shoots off the spent degree. The mass of the degree is 200 kg, the speed of its removal from the apparatus is 10 m / s. How much has the speed of the device changed?**

mk = 2 t = 2000 kg.

mst = 200 kg.

Vst = 10 m / s.

ΔVk -?

Let’s write down the law of conservation of momentum for closed systems: a ship and a stage.

Δpk = pst.

The momentum of a body p is the product of the body’s mass m by its velocity V.

The momentum of the disconnected stage pst should be compensated for by changing the momentum of the spacecraft Δpk.

Since the mass of the ship does not change, it means that Δk = mk * ΔVk

mk * ΔVk = mst * Vst.

ΔVk = mst * Vst / mk.

ΔVk = 200 kg * 10 m / s / 2000 kg = 1 m / s.

Answer: the speed of the spacecraft when the stage is disconnected will change by ΔVk = 1 m / s.