themonk
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Homework Statement
What is the direction of the force \vec{F} on the -10 nC charge in the figure? Give your answer as an angle measured cw from the +x-axis. Problem 26.39 in Physics for Scientists and Engineers Second Edition by Knight
Magnitude of the force is 4.3E-3 N
Homework Equations
As far as I know, this is the only relevant equations:
\vec{F}=k*q_{1}*q_{2}/d^{2}
The Attempt at a Solution
I already found the magnitude as listed above. But I need to find \theta in the clockwise direction.
The force of A (being the -5 nC charge) I figured was direction -4.3E-4 \hat{j} and -1.28E-3 \hat{i} and the other charge had a force of -4.5E-3 I double checked with an answer from someone else (MasteringPhysics also said it was correct). I figured I would use a trigonometric function for the final part, ie the angle measured in the clockwise direction. In lab we used tangent, but was confused as to why (tangent is opposite over adjacent):
tan(\theta)=4.07E-3/1.28E-3 ==> \theta=tan^{-1}(3.179)
which is 72.54 degrees. I added 180 to it to get 252.54, but apparently that is not correct (I don't completely understand the cw and ccw part).
Is there any line of thought that I should proceed with?
(sorry about my English)
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