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Differentiation of potential energy

  1. Mar 14, 2008 #1
    1. The problem statement, all variables and given/known data

    The potential energy of a system of two particles separated by a distance r is given by U(r) = (A)/(r^4), where A is a constant. Find the radial force that each particle exerts on the other. (Use A and r as appropriate in your equation.)

    2. Relevant equations

    F=-dU/dx
    U is potential energy

    3. The attempt at a solution

    i figured out the antiderivative of U(r) is -(A)/(3*r^(3)) but it isnt the correct answer.
    what else do u need to do besides the antiderivative which is equal to force. since it is 2 particles should i divide the U(r) funciton by 2?
     
    Last edited: Mar 14, 2008
  2. jcsd
  3. Mar 14, 2008 #2
    you actually want the partial derivative of r
     
  4. Mar 14, 2008 #3
    ok but how do u get that? im rather new at the whole calculus thing. wud it just b A/3r^3?
     
  5. Mar 14, 2008 #4
    Think of U(r) as A*(r^-4) then try to differentiate it...
     
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