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Homework Help: Inelastic explosion

  1. May 14, 2013 #1
    1. The problem statement, all variables and given/known data

    An object at rest in deep space explodes into two parts converting some of its
    original mass into kinetic energy of the fragments. Both fragments move at a speed of
    0.60 c relative to the position of the original object. Each fragment has a rest mass of
    3.0 kg. Calculate the rest mass of the original object.

    2. Relevant equations

    Conservation of momentum m0v0 = m1v1 + m2v2

    Mass-energy relationship E=mc^2

    3. The attempt at a solution

    Kinetic energy is not conserved since explosion is inelastic. This is when I get stuck: how can I represent the kinetic energy ('lost mass') in the form of momentum?
  2. jcsd
  3. May 14, 2013 #2


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    Momentum will not help you here. The two fragments will have equal and opposite momentum, and there's nothing more to be deduced.
    I'm not sure what you mean by describing the explosion as 'inelastic'. Yes, of course there would be losses in practice, but it seems to me that the question expects you to ignore that..
  4. May 14, 2013 #3

    rude man

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    orig rest energy = post-rest energy + kinetic energy of the two fragments, as seen from the position of the explosion.
    Last edited: May 14, 2013
  5. May 14, 2013 #4


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    welcome to pf!

    hi ftbf22! welcome to pf! :smile:
    total energy is conserved, so just add up the total energies :wink:
    what does momentum have to do with it? :confused:
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