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Homework Help: Problem with power and potential energy

  1. Mar 28, 2010 #1
    1. The problem statement, all variables and given/known data
    Particle mass m is moving along the x-axis.
    The particle is attracted to the principle axis O to measure power mk/x^2 when x>a
    and repels the O with measure power mka/x^3 when 0<x<a, where a,k>0

    i) Find the potential energy of the particle
    ii)The particle is released from rest at 2a from O. Describe the movement to perform the particle and show that the particle will stand briefly when x=a/sqrt2

    3. The attempt at a solution
    i) I tried to find the potential energy by integrating the function of power:

    .............mk / x ^ 2 , x> a
    F (x) =
    .............mka / x ^ 3 , 0 <x <a

    using the relation F (x) = - dU / dx, but the integral constant C if assume that U (O) = 0, goes infinity (oo).

    I still can not design the function of potential energy which found that likely have the form:

    ..............-mk / x , x> a
    U (x) =
    ...............mka / x ^ 2 , 0 <x <a

    ii) For the second question I can not think of anything.
    Last edited: Mar 28, 2010
  2. jcsd
  3. Mar 31, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi costas! :smile:

    (try using the X2 tag just above the Reply box :wink:)
    Then don't assume U(0) = 0 :wink:

    assume U(a) = 0, or U(∞) = 0. :smile:
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