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>>Another mistake you make in your calculations is that you assume that the >>exhausted mass and the exhaust velocity are constant at any time. >>It's quite simple to see that that can't be true: The ship continues to >>become lighter while it exhausts fuel therefore it also becomes easier to >>accelerate. So for a constant mass exhaust and a constant exhaust velocity >>you'll accelerate with an increasingly larger rate. > >Ah, no I included this in the total mass calculations. Indeed you did include the fact that the ship became lighter, but not that it would accelerate with a greater rate. You explicitly defined a=10 m/s/s (Don't forget that 2nd /s otherwise your talking about velocity.) The "t" in your formulas has a double meaning, which is why you confuse yourself. The "t" in a(M + Mf * T - Mf * t) is an actual point in time, while the "t" in (Mf * Vf) / t is actually a "dt", thus a per unit of time. In short the relation m*a = (Mf * Vf)/t isn't valid if m changes during t. Timothy

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