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Homework Help: Finding the speed v of the proton

  1. Oct 28, 2015 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    Principle of conservation of momentum,

    3. The attempt at a solution
    Since the nucleus is stationary, initial momentum is zero.
    Unified atomic mass constant, a.m.u = 1.66 x 10^-27
    Mass of the new nucleus: (A-4) x a.m.u
    Mass of proton: 4 x a.m.u
    0= ((A-4) x a.m.u )(u) + (4 x a.m.u )(-v)
    4v = (A-4) u
    v= (A/4 -1) u
    So I chose A,
    But the answer is B, where have I gone wrong?
  2. jcsd
  3. Oct 28, 2015 #2


    User Avatar

    Staff: Mentor

    Why did you subtract 4 mass units from the atom when it only emitted a single proton? Were you thinking alpha particle?
  4. Oct 29, 2015 #3
    Oh yeah, I was. :nb)
    thanks for the help :smile:
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