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## Homework Statement

Four charges,

q1 = +195 µC, q2 = +60 µC, q3 = −145 µC, and q4 = +21 µC,

are fixed at the corners of a 4 m by 5 m rectangle, as illustrated in the figure below. What are the magnitude and the direction of the net force acting on q1? (Assume the x-axis extends from q1 to the right.)

q3--------------------q2

| |

| |

| |

q4--------------------q1

## Homework Equations

F = k q1q2/r2

## The Attempt at a Solution

I have followed the steps outlined here. http://dev.physicslab.org/Document....lectrostatics_AdvancedCoulombsLawProblems.xml

For Fq1q2 I get 26.30N

Fq1q4 I get 5.89N

and for Fq1q3 I get 24.82

I proceed to chart it as shown F X Y

q1q2 0 -26.30

q1q4 5.89 0

q1q3 24.82cos135°=-17.55 24.82sin135°=17.55

-11.66 8.75

Then F = sqr.rt(-11.66)^2+(8.75)^2

=14.58

Then a=tan-1|8.75 /-11.66|

=-36.89

θ=180-36.89

=143.11°

Neither of which are the proper answers apparently. What am I doing wrong? Any help would be greatly appreciated.