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

Three identical point charges Q1, Q2, and Q3 all having charge 3 microCoulombs are located at the vertices of an equilateral triangle with sides s=3 m. How much work would I have to do to move Q1 to a point on the line connecting Q2 and !3 (which are fixed) if this point is a distance .4 s from Q2 and a distance .6 s from Q3?

http://img129.imageshack.us/img129/1091/trianglejp1.th.gif [Broken]

(Picture obviously not drawn to scale)

2. Relevant equations

W = Fd = qEd

E = kQ/d

3. The attempt at a solution

I am using q = 3*10^-6 Coulombs in all of my attempts. The thing that is throwing me off is what to use as the distance and electric field.

I did two different approaches:

Attempt 1

First I tried to find the distance between Q1 and its destination point. I just made a right triangle:

http://img98.imageshack.us/img98/1240/88380904mi7.gif [Broken]

And the hypotenuse was sqrt(2.34).

Then,

E = kq/d

E = (9*10^9)(3*10^-6)/sqrt(2.34)

E = 17650.45216 N/C

So I plugged in E to the formula for Work

W = qEd

W = (3*10^-6)(17650.45216)(sqrt(2.34))

W = .081 J

Attempt 2

I tried to calculate the electric field at the point Q1 between Q2 and Q3. For distance i used 1.2 (.4*3m) and 1.8 (.6*3m).

First,

E_tot = E1 + E2

E=kq/d^2 (electric field at a point between two charges)

E1=(9*10^9)(3*10^-6)/1.2^2

E1=18750

E2=(9*10^9)(3*10^-6)/1.8^2

E2=-8333.34 (rounded up, because it was .3 repeating, negative because the direction of the field that acting on Q1 is to the left)

E_tot = E1+E2

E_tot = 18750 - 8333.34 = 10416.67

Then,

W = qEd

d will remain the same as in attempt 1.

W = (3*10^-6)(10416.67)(sqrt(2.34))

W = .0478 J

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There you have it. Neither of them were the right answer. Please help. I know I am close but like I said, I am confused as what to use for E and d. Thank you.

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# Homework Help: Work Needed to Move a Charge

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