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Modeling rocket displacement

  1. Jul 31, 2007 #1
    I'm trying to model (purely for my own edification) the behavior of a rocket (specifically w.r.t. significant mass loss over time). I *think* I have everything correct, but I'm not totally confident with how I'm computing the vertical displacement (assuming no air resistance)

    I have the following:
    [tex] m(t) = m_{rocket+fuel} - \dot m t[/tex]
    [tex]v_{rocket}(t) = v_{eject} \cdot ln \left ( m_{rocket+fuel} \over m(t) \right) - g t[/tex]
    [tex]{\dot m} = {F_{thrust} \over v_{eject}}[/tex]
    [tex]E_k(t) ={{ m(t) \cdot v(t)^{2} } \over 2}[/tex]

    Hopefully so far I'm ok...I'm assuming constant thrust force and eject velocity, which I am given to understand is ok. I'm also neglecting air resistance.

    My reasoning is that since I'm starting from 0 velocity, 0 kinetic energy (I know, rotation of the earth, etc. la la la I can't hear you :tongue2:), the total kinetic energy is the work done, so I have distance:
    [tex]d(t) = {E_k(t) \over F_{thrust}}[/tex]

    Is there a better way? I'm working (slowly) on integrating v(t), but it's really quite hairy. And my calc (like my physics) is, well, very poor. (i.e. self taught). I have a spreadsheet where I've got some numbers generated by the above, so if it would be helpful to post those, I can do so.
  2. jcsd
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