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Thrust created

  1. Oct 24, 2012 #1
    The burned gases of a rocket engine are ejected from the rocket nozzle at a speed of 17,000 ft/sec. If the weight of gas ejected is one pound per second, find the thrust developed by the rocket.

    I don't really have an equation to use here but my guess is F = M\32.2 * Ejection Velocity

    F in lbs. = [ 1 lb / 32.2] * 17,000 = 527 lbs of thrust

    Anyone care to verify that this is correctly calculated or have any ideas on a different calcualtion?
  2. jcsd
  3. Oct 24, 2012 #2


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    Analysis of units does not support your approach. Also 32.2 ft/s2 is the terrestrial acceleration due to gravity. The rocket could be anywhere-- interstellar space or the moon. Thrust is a function of the rocket, not gravity.
    Last edited: Oct 24, 2012
  4. Oct 28, 2012 #3

    Your work looks correct to me. 1 lbf=32.4 Lbm*ft/Sec2
    The units of thrust is lbf
  5. Oct 29, 2012 #4


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    This part got me-- "the weight of gas ejected is one pound per second". I read this as a dm/dt of 1lbf/s. If this is read as 1lbm/s then things to fall into place.
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