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Homework Help: What is meant by momentum is maximised?

  1. Feb 9, 2010 #1
    1. The problem statement, all variables and given/known data

    I'm answering some questions to do with rockets and their momentum after 250s of engine time

    fuel rate of rocket= 480 kg/s
    initial exhaust speed= 3.27 km/s
    final velocity: 12.2 km/s
    m (fuel at t=0) = 1.81*10^5 kg
    m(total at t=0) = 2.55*10^5 kg
    m (total at t=250s) = 68400 kg

    associated questions have been pretty simple so far like:
    find the final velocity
    find the ration of masses if the final speed was ...

    2. Relevant equations

    I'm stumped on the meaning of the phase "momentum is maximised"
    (not lookign for someone to do my homework)

    the phrase I'm stumped on:
    A rocket starts moving from rest in deep space. What fraction of its initial mass does the
    rocket (i.e. casing plus payload plus remaining fuel) have when its "momentum is maximised"

    what is the definition of maximised momentum? The larger the final velocity, the larger the momentum and this all depends on the feul rate from which the rocket uses (the amount of feul 480kg/s)
    Anyway if anyone can understand what is meant by "momentum is maximised" that would be great.

    3. The attempt at a solution
  2. jcsd
  3. Feb 9, 2010 #2


    User Avatar

    http://img14.imageshack.us/img14/2735/momentuum.jpg [Broken]

    Here is a graph of you problem. More exactly the momentuum of your rocket as a function of time. It has a maximum right there.
    Last edited by a moderator: May 4, 2017
  4. Feb 19, 2010 #3
    thanks lok, I wasn't thinking at all.
    I took dp/dm=0 to get maximum initial mass?
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