Posted by **LS** on Tuesday, October 16, 2012 at 11:05pm.

Three charges, q1=+45.9nC q2=+45.9nC and q3=+91.8nC are fixed at the corners of an equilateral triangle with a side length of 3.70cm. Find the magnitude of the electric force on q3.

- Physics HELP!! -
**Elena**, Wednesday, October 17, 2012 at 4:34am
k =9•10^9 N•m²/C²

r=0.037m

F13=k•q1•q3/r²,

F23=k•q2•q3/r²,

Cosine law for forces:

F=sqrt[F13²+F23²- 2•F13•23•cos120°]

- Physics HELP!! -
**Erica**, Friday, February 22, 2013 at 2:58pm
Elena, why do you have a 13 & 23 beside F? Or is this just to distinguish between the two forces

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