Solving an Electrostatic Force Problem

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Homework Help Overview

The problem involves calculating the electrostatic force between point charges, specifically focusing on the forces acting on a third charge due to two other charges positioned symmetrically along the x-axis. The subject area is electrostatics.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the total electrostatic force by considering the symmetry of the charge arrangement and focusing on the y-components of the forces. Other participants raise questions about the distance used in calculations and the correctness of units.

Discussion Status

The discussion is ongoing, with participants exploring different aspects of the problem, including unit checks and the validity of the original poster's calculations. Some participants suggest that the original problem statement may contain an error based on their reasoning about the expected order of magnitude for the force.

Contextual Notes

There is a mention of potential discrepancies in the expected answer, with participants questioning the accuracy of the problem statement and the calculations involved. The original poster expresses uncertainty about their result compared to the expected answer.

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I'm stuck on the following problem: Point charges of q_1=-12nC are placed at (-4,0) cm and (4,0) cm. Determine the magnitude of the electrostatic force on a third charge of q_2=20nC placed at (0,8) cm. So because of symmetry I figured that the x-components of the forces will cancel each other and the total force will be 2 times the y-component. So I did 2*k*q_1*q_2*sin63.4/(0.04^2+0.08^2) and got 4.8e-4 N but the answer is supposed to be 3.1e-8 N. Any help would be appreciated, thanks.
 
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What about the distance (r) ?
 
Just check all your units. That's usually the problem when your off by several orders of magnitude.
 
Last edited:
my r^2 is (0.08^2+0.04^2). I'm pretty sure my units are right, I did 2(8.99e9)(12e-9)(20e-9)(sin63.43)/(0.08^2+0.04^2) = 4.8e-4 N
 
It looks like your answer is correct. If you copied the problem correctly, the solution must be wrong. This is clear if you do an order of magnitude estimate: the charges are of order 10^-8 C, and they are separated by about 10^-1 m, so the force should be of order 10^10*10^-8*10^-8/(10^-1)^2, or about 10^-4 N.
 

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