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Homework Help: Finding the electric potential energy

  1. Feb 5, 2012 #1
    A charge of -2.580 mu C is located at (2.575 m, 4.742 m), and a charge of 1.440 mu C is located at (-2.730 m, 0). Find the electric potential at the origin.

    q_1= -2.580*10^-6 C
    q_2= 1.440*10^-6 C
    k = 8.99*10^9 N*m/C^2
    r_2= -2.730 m

    V= (k*q_1)/r_1 + (k*q_2)/r_2

    So first i found r_1 by using the Pythagorean theorem r_1= √(2.575^2 +4.742^2)= 5.396 m
    Then i plugged all the information into the above equation (converting the mu C to C) i came up with the answer -9040 V but it's the wrong answer and i can't figure out what i did wrong.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 5, 2012 #2
    Check your math. Using your numbers I got a potential of about -4300 V due to the negative charge. The positive charge would only make that number bigger, I can't get your number?
  4. Feb 5, 2012 #3


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    Hello sameasabuv. Welcome to PF!

    Don't forget, q1 and q2 have opposite sign.
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