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Homework Help: A Rocket in Deep Space

  1. Mar 4, 2009 #1
    1. The problem statement, all variables and given/known data

    A rocket is fired in deep space, where gravity is negligible. In the first second it ejects 1/160 of its mass as exhaust gas and has an acceleration of 15.9 m/s2.

    What is the speed vgas of the exhaust gas relative to the rocket?
    Express your answer numerically in kilometers per second.

    2. Relevant equations

    conservation of momentum: (m1v1 + m2v2)final = (m1v1 + m2v2)initial

    3. The attempt at a solution

    (159/160)M(vrocket + 15.9) - (1/160)Mvgas = Mvrocket

    I go on to simplify it but I cant express vgas in numerical terms, as vrocket still remains in the equation. There is no value given for this so how can I solve the question?

    Pls help! Thanks! :)
  2. jcsd
  3. Mar 4, 2009 #2


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    Homework Helper

    What's wrong with F = m*a = Δmv/Δt ?
  4. Mar 4, 2009 #3
    hmmm... Are you saying that i should use m*a = Δmv/Δt for the change in momentum of the rocket? then wat will be the value of m? :confused:
  5. Mar 4, 2009 #4
    ooohh!!! I got it now! Thanks for the help! :)
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