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Homework Help: Proton AND Work-Energy Theorem

  1. Feb 29, 2004 #1
    Can some one help me out here, I have tried using several different methods but I still don't know what I am doing wrong.

    The question is:

    A proton in a high energy accelerator moves w/a speed of 0.5c, use the work-energy theorem to find the work required to increase its speed to 0.7c.

    I have tried /\K=.5m(vf^2-vi^2), what am I doing wrong????
  2. jcsd
  3. Feb 29, 2004 #2
    You're not taking into account relativistic effects.

  4. Mar 1, 2004 #3

    I don't know what your talking about,

    I thought I would use:

    .5m( (.7*c)^2-(.5*c)^2)

    c= the speed of light

    I was also told an equation like m^2c^2((1/sqrt(1-(v^2/c^2)))-1), but I kept geting zero for my answer and the actual answer is like 3.69??e-11, but I do not know how they got this answer??
  5. Mar 1, 2004 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Re: Ugh!?

    This is only correct for low, non-relativistic speeds.
    Use the relativistically correct expression for KE:
    KE = mc^2((1/sqrt(1-(v^2/c^2)))-1)
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