(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

What is the direction of the force [tex]\vec{F}[/tex] 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

2. Relevant equations

As far as I know, this is the only relevant equations:

[tex]\vec{F}[/tex]=[tex]k*q_{1}*q_{2}/d^{2}[/tex]

3. The attempt at a solution

I already found the magnitude as listed above. But I need to find [tex]\theta[/tex] in the clockwise direction.

The force of A (being the -5 nC charge) I figured was direction -4.3E-4 [tex]\hat{j}[/tex] and -1.28E-3 [tex]\hat{i}[/tex] 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([tex]\theta[/tex])=4.07E-3/1.28E-3 ==> [tex]\theta[/tex]=tan[tex]^{-1}[/tex](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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# Homework Help: Magnitude and Direction of a charge interaction

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