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Homework Help: Three electrons form an equilateral triangle

  1. Mar 25, 2015 #1
    1. The problem statement, all variables and given/known data

    Three electrons form an equilateral triangle 1.00nm on each side. A proton is at the center of the triangle. What is the potential energy of this group of charges?
    Known Variables:
    s = 1.00 × 10-9m
    p+ Charge = 1.60 × 10-19C
    e- Charge = -1.60 × 10-19C
    r = s/√(3) = 5.77 × 10-10m

    2. Relevant equations

    ΔU = (kq1q2)/ r

    3. The attempt at a solution

    ΔU = k[(3(-1.60×10-19)2))/(1.00×10-9) - ((3(1.60×10-19)(-1.60×-19))/(5.77 × 10-10))]

    For some reason I cannot get the answer, and I was wondering if anyone could spot my error. Thanks!
  2. jcsd
  3. Mar 25, 2015 #2


    User Avatar
    Homework Helper
    Gold Member

    The term with denominator 5.77x10^-10 should be negative but you have a double minus sign which makes it positive. The potential energy of the proton due to the 3 electrons should be negative due to the attraction.
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