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Help with Newtons 2nd applied to Rocketry

  1. Jul 25, 2008 #1
    This is a direct quote from nasa.gov. I understand everything up until the last equation.

    Can it not be written like F = mdot(v2-v1) ?

    Also, this equation F = d(mv)/dt is the same as this F = (m dot * V)e - (m dot * V)0 ? Or no?

    I understand Mass x Velocity is momentum and they want the change in momentum but at the same time mass AND velocity are changing with respect to time.

    I guess i dont understand why they wrote it like F = (m dot * V)e - (m dot * V)0 , including mdot twice.
     
  2. jcsd
  3. Jul 27, 2008 #2

    mukundpa

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    Homework Helper

    I think it is more clearer if we write

    F = m(dv/dt) + v (dm/dt) = m*(v dot) + v (m dot)
     
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