Need help finishing Physics Problem, almost have answer.?

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Frogger Man
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Two Q = +5.85 mC charges are placed at opposite corners of a square d = 1.2 m on each side, and -Q = -5.85 mC charges are placed at the remaining corners, as shown in the figure.

I labeled the square A, B, C, D from top left to bottem left.

Fba = k • QA • QB / dBA2
Fca = k • QA • QC / dCA2
Fda = k • QA • QD / dDA2

Fba= -.21365
Fca= .10683
Fda= -.21365

I used the pythagorean therum to find Fba+Fda, and got .302, and then i subracted .10683 from that, but that was not the correct answer.

Any suggestions?
 

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Yea, probably should have put that in,

Determine the magnitude and direction of the force on each charge.
 
Frogger Man said:
Fba= -.21365
Fca= .10683
Fda= -.21365
What units are these in?
 
They should be in Newtons
 
Fba = k • QA • QB / dBA2
Fba = (8.99*10^9 • (5.85)*10^-6 • (-5.85)*10^-6) / 1.2^2
Fba = (-.30766) / (1.44)
Fba = -.21365

Are my numbers off, or just my sign, or both?
 
Ah... you're using mC to mean microCoulombs. (Better to use [itex]\mu C[/itex].) In that case, the numbers look OK to me.
 
I think you might be right, it should be milli. I will try that.
 
I got it, 195872.2698.

Thanks for your help.