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## Homework Statement

Three point charges are located at the corners of an equilateral triangle as shown in Figure P15.13 (q = 3.00 µC, L = 0.400 m). Calculate the net electric force on the 7.00 µC charge.

° (counterclockwise from the +x axis)

http://www.webassign.net/pse/p23-07alt.gif

## The Attempt at a Solution

F_12 = 8.9875 x 10^9 (3e-6)(7e-6)/.4e2 =

**1.18 N**

F_13 = 8.9875e9 (7e-6)(4e-6)/.4e2 =

**1.57 N**

then

F_12x = 1.18cos60 =

**.59 N**

F_12y = 1.18sin60 =

**1.0219 N**

F_13x = 1.57cos60 =

**.785 N**

F_12y = -1.57sin60 =

**-1.3697 N**

then i added them up

Fx = .59 + .785 =

**1.375 N**

Fy = -1.3597 + 1.0219 =

**- .3378 N**

I know that to get the degree its arctan Fy/Fx but i get the incorrect answer. Is there something wrong in the equation or im i using the wrong number?

I understand how to do the first part which is 1.4 N of electric force on 7uC charge.

Thanks for any help.