# (Un) Realistic Situation 1

Two fat astronauts each of mass $$120 kg$$ are traveling in a closed spaceship moving at a speed of $$15 km s^{-1}$$ in the outer space far away from any other object. The total mass of the spaceship including the astronauts is $$660 kg$$.

If the astronauts try to do slimming exercise & succeed in bringing their weights down to $$90 kg$$ each (this is sure to make the women jealous), with what velocity will the spaceship finally move in $$km s^{-1}$$?

You can also try (Un) Realistic Situation #2.

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