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Homework Help: Modern Physics question -- an atom ejecting a relativistic electron

  1. Sep 27, 2016 #1
    1. The problem statement, all variables and given/known data.
    An atom at rest can undergo radioactive decay, ejecting an electron at a maximum speed of 0.5c. If the atom in a particle accelerator is observed to produce an electron traveling at 0.75c, at least how
    fast must the atom itself have been moving?

    2. Relevant equations
    u0 x =(ux −v )/(1−uxv/c^2)

    3. The attempt at a solution
    The problem is asking for the speed of the atom,

    I set
    After plugin in, I get the result of -0.4c

    I don't feel sure aboout this anwser.
    Any suggeestions? Corrections?
    Last edited by a moderator: Sep 27, 2016
  2. jcsd
  3. Sep 27, 2016 #2


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    You just have to sort out the minus sign!
  4. Sep 27, 2016 #3
    So the awnser is simply 0.4c?
  5. Sep 28, 2016 #4


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    What you didn't do was set the problem up in any meaningful way. Why did you use the equation you did? Can you not check an answer of 0.4c yourself?
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