Simple degree help (tan-1 fy/fx)

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Homework Help Overview

The problem involves calculating the net electric force on a charge located at the corners of an equilateral triangle, specifically focusing on the angle derived from the force components.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the angle using arctan of the force components but questions the accuracy of their result. Other participants inquire about the angle obtained and suggest considerations for adjusting the angle based on the direction of measurement.

Discussion Status

Participants are actively discussing the angle calculation, with some suggesting adjustments to the angle based on different reference points. There is no explicit consensus on the correct approach yet, but the conversation is exploring various interpretations of the angle measurement.

Contextual Notes

There is a mention of confusion regarding the addition of angles (180 vs. 360 degrees) in relation to the counterclockwise measurement from the x-axis.

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Homework Statement



Three point charges are located at the corners of an equilateral triangle as shown in Figure P15.13 (q = 3.00 µC, L = 0.400 m). Calculate the net electric force on the 7.00 µC charge.

° (counterclockwise from the +x axis)

http://www.webassign.net/pse/p23-07alt.gif

The Attempt at a Solution



F_12 = 8.9875 x 10^9 (3e-6)(7e-6)/.4e2 = 1.18 N

F_13 = 8.9875e9 (7e-6)(4e-6)/.4e2 = 1.57 N

then

F_12x = 1.18cos60 = .59 N
F_12y = 1.18sin60 = 1.0219 N
F_13x = 1.57cos60 = .785 N
F_12y = -1.57sin60 = -1.3697 N

then i added them up

Fx = .59 + .785 = 1.375 N
Fy = -1.3597 + 1.0219 = - .3378 N

I know that to get the degree its arctan Fy/Fx but i get the incorrect answer. Is there something wrong in the equation or I am i using the wrong number?

I understand how to do the first part which is 1.4 N of electric force on 7uC charge.

Thanks for any help.
 
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What angle are you getting??
 
i get -13.80*

if i add 180 to that i get 166.2*

both are incorrect.
 
Wouldn't you want to add 360 to it? That would give you the angle from the x-axis going counterclockwise instead of clockwise. Just a guess.
 
Last edited:
You are correct. it is adding 360.

I thought it was 180 because i was thinking of a triangle which is 180*.

Thanks again.