# Homework Help: Work done to move a point charge

1. Jan 29, 2013

### dfetnum

1. The problem statement, all variables and given/known data
Three charges, q1, q2, and q3, are located at the corners of an equilateral triangle with side length of 1.49 m. Find the work done in each of the following cases:

a) to bring the first particle, q1 = 1.33 pC, to P from infinity
b) to bring the second particle, q2 = 2.99 pC, to Q from infinity
c) to bring the last particle, q3 = 3.29 pC, to R from infinity
d) Find the total potential energy stored in the final configuration of q1, q2, and q3.

2. Relevant equations
W=qV=kqq/r

3. The attempt at a solution
I've tried doing kq1q2/r +kq1q3/r and got 5.05E-14 Nm but I don't think this is the correct method

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Last edited: Jan 29, 2013
2. Jan 29, 2013

### Dick

Calculating differences in potential energy is the correct method. But which part is that supposed to be the solution of? Start with a).

3. Jan 29, 2013

### dfetnum

that is my attempt at a. I need to find the potential energy from the two different charges and then add them

4. Jan 29, 2013

### Dick

When you move the first charge in there are no other charges around. You haven't placed any other charges yet. a) should be super easy.

5. Jan 29, 2013

### dfetnum

so, what equation would that be? The one I am using still has a radius and a place for a second charge

6. Jan 29, 2013

### Dick

The initial charge is q=0. Put that in.

7. Jan 29, 2013

### dfetnum

oh wow, I didnt realize that the total work done was zero if there was no other charge to push against it. Cool, I figured out the rest. Thanks

8. Jan 29, 2013

### Dick

Right. Moving the first charge in is free.

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