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Homework Help: Force using relativistic momentum

  1. May 16, 2008 #1


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    [SOLVED] Force using relativistic momentum

    I have an example problem in a textbook I'm reading:

    "Find the acceleration of a particle of mass m and velocity v when it is acted upon by the constant force F, where F is parallel to v.

    then it proceeds to show the solution:

    [tex]F = \frac{d}{dt}(\gamma mv) = m\frac{d}{dt}(\frac{v}{\sqrt{1-v^{2}/c^{2}}})[/tex]

    I get all that so far. The next step is where it loses me:

    [tex]= m[\frac{1}{\sqrt{1-v^{2}/c^{2}}} + \frac{v^{2}/c^{2}}{(1-v^{2}/c^{2})^{3/2}}] \frac{dv}{dt}[/tex]

    so I don't know how they got there... and then the next step confuses me also. They go from above to here:

    [tex]= \frac{ma}{(1-v^{2}/c^{2})^{3/2}}[/tex]

    and then of course there a few more steps after that one, but I can get those, I'm just confused about those two steps. Please help clarify it for me, thank you.
  2. jcsd
  3. May 16, 2008 #2

    Doc Al

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    Staff: Mentor

    The first step: Use the product (or quotient) rule for taking a derivative.
    The second step: Simplify. Start by getting a common denominator.
  4. May 16, 2008 #3


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    ah, of course. I see it now. Thank you for the quick reply.
  5. Nov 8, 2009 #4
    Re: [SOLVED] Force using relativistic momentum

    I still can't Simplify it to the final form .. can anybody help me with that?? Thank you
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