Electrical potential energy: 3 charges in a line

  • Thread starter alicemunro
  • Start date
1. The problem statement, all variables and given/known data

A positive charge, q1 is at (-20cm,0). An equal and opposite charge q2 is at (20cm, 0). A positive charge q3, equal to q1, is placed at (60cm,0). What is the potential energy of the three charges??


2. Relevant equations

EPE= kq / r


3. The attempt at a solution
EPE = k( (5 X 10^-9)/.2) + (5 X 10^-6)/.6) - (5 X 10^-6)/.2))
= wrong answer
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
 
1. The problem statement, all variables and given/known data

A positive charge, q1 is at (-20cm,0). An equal and opposite charge q2 is at (20cm, 0). A positive charge q3, equal to q1, is placed at (60cm,0). What is the potential energy of the three charges??


2. Relevant equations

EPE= kq / r


3. The attempt at a solution
EPE = k( (5 X 10^-9)/.2) + (5 X 10^-6)/.6) - (5 X 10^-6)/.2))
= wrong answer
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
It looks like you have additional information to provide such as the charges of q1,q2, q3 also your equation for electric potential energy is incorrect should be:
[tex] U = k \frac{q_a q_b}{r_{ab}}[/tex]
Finally I need to note that r is not the position but rather the relative distance between charges a and b. With these adjustments the answer should clear up a bit
 

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