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Am i doing this right

  1. Mar 21, 2005 #1


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    So the problem is

    An unstable particle with a mass of 3.34 x 10^-27kg is initially at rest. The particle decays into two fragments that fly off along the x-axis with velocity components 0.987c and -0.868c. Find the amsses of the fragmments. (Suggestion: Conserve both energy and momentum).

    So i setup ymv = ymv (for the second)
    I figured out both y's
    I then used E=mc^2 to find the rest energy and got like, 3.0x10^-10
    I divided that in half and then used (y-1)mc^2 (At this point in the post i realized what i did wrong i hope lol)
    to figure out what mass would give 1.5x10^-10

    That would give me each mass.... am i correct?
    Im re-doing my steps as we spoke so i hope im right :D


    Ok so i did still do it wrong... i still need help :)
    Last edited: Mar 21, 2005
  2. jcsd
  3. Mar 21, 2005 #2
    I am a little confused by your description of the set up.
    You would be good to follow the following method:
    1) convert 3.34X10^-27 kg to eV/c^2
    2) use you energy relation to solve for one of the two masses(since they must be different to conserve momentum for linear trajectories to one another)
    3) solve for your momentum. gamma1*m1*v1=(-1)*gamma2*m2*v2(since one velocity is along the neg x and the other along the positive x)
    4) now you should have two equations with two unknowns, so it is ready to be solved.

    By my calc(with some round off) you should get m1(v=.987c) approx.=140 MeV/c^2
    and m2 approx. = 500 MeV/c^2

    Like I said these are not exact but close. You can always check if iyour solution is right with the energy or momentum conservation.
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