WEBVTT

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So the last question
we can ask us

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is what it was that v0 here
initially off the sled,

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making use of the fact
that the sled comes

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to a stop at the time that
the fuel is all used up.

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That means that our final
velocity over here is 0.

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We'll bring v0 to
the other side,

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and then we get to minus u l n.

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And the rocket
mass, by then it's

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just the dry mass-- n0 over 2n0.

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And that, of course,
cancels out here.

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And we can say that
is plus u l n of 2.

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So that was the velocity
that the sled was going with.