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Rocket thrust question

  1. Oct 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A jet aircraft is traveling at 246 m/s in horizontal flight. The engine takes in air at a rate of 77.0 kg/s and burns fuel at a rate of 4.00 kg/s. If the exhaust gases are ejected at 633 m/s relative to the aircraft, find the thrust of the jet engine and the delivered power.

    find thrust and power

    ive tried everything! even my teacher couldnt get the problem. but i refuse to just accept that i cant get it..please help would be greatly appreciated!
     
  2. jcsd
  3. Oct 21, 2008 #2
    If you've tried everything maybe you could show at least some of it.
     
  4. Oct 22, 2008 #3
    ahh yes, sorry about that.

    here's what i know. i know that it change in momentum is obviously is impulse. So i have it set to a 1 second time frame, and i found:

    initial momentum = ((77 kg + 4 kg) * 246 m/s) = 19926 kg*m/s
    TOTAL MASS * VELOCITY = Momentum

    final momentum = ((77 kg + 4 kg) * -387 m/s) = -31347 kg*m/s
    TOTAL MASS * VELOCITY = Momentum

    the change in that would become the average force because impulse (which is change in momentum) is equal to average force * time. and the time is set to 1 in this instance.

    anybody see flaws in the thinking?
     
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