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Homework Help: Unusual difficult kinetic problem

  1. Sep 27, 2010 #1
    1. The problem statement, all variables and given/known data
    http://img80.imageshack.us/img80/1797/20799357.png [Broken]

    2. Relevant equations
    General kinetics formulas

    3. The attempt at a solution
    Actually I don't know how to start. The initial mass is M when qm energy is used the mass is M-m. If I use an energy balance I must use the integral version, right?

    [tex] \int m(t) v \mbox{d}v = qm [/tex]

    But I don't know how to start.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 27, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    I myself have never done this before, but I will try to help you. I think my way should get the required formula.

    Consider the exhaust gases (a small amount 'dm') at time 't'.

    Initial momentum pt= dm*ve

    Final momentum pt+dt = dm(vR-ve)

    Rocket:

    pt=(M-dm)vR
    pt+dt= (M-dm)(vR-ve).

    Now use conservation of momentum here: Loss in change of momentum in gas = change momentum gained by rocket

    Using this, you should now be able to get a differential equation to solve (remember, 'dm' is infinitesimally small)
     
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