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Homework Help: Electric Potential Energy help

  1. Jan 26, 2007 #1
    I did all I can, and I'm stressed out over this. Thus, here I am. :(

    Here's the question (I substitute the numbers with alphabet letters):

    >Two point charges of magnitude of A nC and -B nC are separated by D m distance.
    >The acceleration of gravity is 9.8 m/s^2. The Coulomb constant, k, is 9x10^9 N*m^2/C^2.
    >What is the potential energy of the PAIR of charges? Answer in units of J.

    So, what I did was find the potential difference, V, between the 2 charges, q1 and q2, at their respective points which has the distance of D using the equation:

    V1 = (k*q1)/D
    V2 = (k*q2)/D

    Then find the electric potential energy(EPE) for each charge with the equation:

    EPE1 = V1 * q2
    EPE2 = V2 * q1

    *(EPE1 and EPE2 are basically the same number)

    And the total potential energy of the 2 charges is:

    EPE(net) = EPE1 + EPE2

    Answer is negative because q2 is -B which has negative value x 10^-9

    If anyone spot any error or have any idea of what I did wrong, please do tell. Perhaps, I missed a step of taking acceleration of gravity into account somewhere? Thanks.
    Last edited: Jan 27, 2007
  2. jcsd
  3. Jan 27, 2007 #2


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    You have calculated the electrical potential energy, but what about gravitational potential energy?
  4. Jan 27, 2007 #3
    I've just now recieved an email from my professor that this problem was cancelled due to computer grading error. I believe what I did as correct though. Thanks for all the help :)
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