Work done to move a point charge

[dfetnum]

Homework Statement

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.

Homework Equations

W=qV=kqq/r

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

 

[Dick]

Homework Statement

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.

Homework Equations

W=qV=kqq/r

The Attempt at a Solution

I've tried doing kq1q2/r +kq1q2/r and got 5.05E-14 Nm but I don't think this is the correct method

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

 

[dfetnum]

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

 

[Dick]

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

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.

 

[dfetnum]

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

 

[Dick]

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

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

 

[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

 

[Dick]

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

Right. Moving the first charge in is free.