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Accelerating force due to ejection

  1. Sep 8, 2008 #1
    A festival rocket is ejecting 0.05 kg of gases per second at a velocity 400m/s The accelerating force on the is? The formula given in the book is F=dp/dt What does the formula mean:confused:
  2. jcsd
  3. Sep 8, 2008 #2


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    The formula is known as Newton's second law and states that the net force acting on a body is equal to the rate of change of the [linear] momentum of the body.
    Last edited: Sep 8, 2008
  4. Sep 8, 2008 #3


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    Welcome to PF!

    Hi Jowin! Welcome to PF! :smile:
    I'll just add:

    p is momentum, which is mass times velocity: p = mv.

    F = dp/dt is the official version of good ol' Newton's second law …

    so it's F = d(mv)/dt = m dv/dt + v dm/dt, which for fixed m is F = m dv/dt, which is probably what you recognise. :wink:

    But for space rockets and festival rockets, m changes, so the official version has to be used! :biggrin:
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