Question: Three point charges, which are initially at infinity, are placed at the corners of an equilateral triangle with sides d. Two of the point charges have a charge of q. If zero net work is required to place the three charges at the corners of the triangle, what must the value be of the third charge?(adsbygoogle = window.adsbygoogle || []).push({});

What I did:

q = 2 of the charges

z = the third charge

d = the final distance between each charge

[tex] 0 = Uelec_q + Uelec_q + Uelec_z [/tex]

[tex] 0 = kq(\frac{-1}{d}) + kq(\frac{-1}{d}) + kz(\frac{-1}{d})[/tex]

[tex] 0 = \frac{-2kq}{d} - \frac{kz}{d} [/tex]

[tex] -2q = z [/tex]

The correct answer is [tex] \frac{-q}{2} = z [/tex]

Can anyone see what I did wrong? I've tried this problem a few times and have gotten the same answer each time.

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# Homework Help: Point charge help

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