# Electric Potential Energy Problem

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1. Feb 21, 2015

### KayDe

1. The problem statement, all variables and given/known data

Two Charged Objects (Q1= -9.0nC & Q2= 15nC) are fixed in place on the +x-axis. The first charge is 12 cm to the left from the origin the other is 12 cm to the right from the origin. A proton is moved from the origin to a position on the +y-axis 9.0 cm from the origin. a) What is the change in potential energy of the proton due to Q1 & Q2?

2. Relevant equations
As given in our Course

F=k |(q1q2)| / r2
E=k |q| / r
Potential Energy (uniform electric field) = qEΔd
Potential Energy (not in uniform electric field) = KQq(1/rf-1/ri)
[rf= final distance ; ri= initial distance]

3. The attempt at a solution

I tried calculating the electric field at the origin between the two points due to the two charged objects. I figured I needed to calculate the electric field since there is not a uniform electric field with two different point charges present. With the electric field I then tried to calculate the electric potential energy since I know the distance and the charge of the proton. I then did the same for the final position and then calculated the change in the potential energy. The given solution for this problem is 1.44 x 10-17 J which I did not get. I either am approaching this the wrong way, understanding it wrong or calculating the wrong things but I get a different answer every time and I'm not sure what I'm missing . Thank You

2. Feb 21, 2015

### Staff: Mentor

You won't need the values of the electric field here. You just need the electric potential energy of the proton in its initial and final positions.

3. Feb 21, 2015

### KayDe

I tried that too but I'm still not getting the right solution :/

4. Feb 21, 2015