Calculating Electric Force on a Charge

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Homework Help Overview

The discussion revolves around calculating the electric force on a charge (Q2) in a system involving three charges (Q1, Q2, Q3) with specified magnitudes and distances. The participants are exploring the interactions between these charges using Coulomb's law.

Discussion Character

  • Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of forces between the charges, questioning the cancellation of forces and the directionality of the forces involved. There is an exploration of the signs associated with attractive and repulsive forces.

Discussion Status

The discussion is active, with participants providing insights into the nature of the forces and their directions. Some guidance has been offered regarding the addition of forces and the interpretation of their signs, but uncertainty remains about the calculations and assumptions made by the original poster.

Contextual Notes

Participants are navigating the implications of charge signs and distances in their calculations, with an emphasis on the need for clarity in how forces are combined. The original poster expresses confusion about the expected outcome of the problem.

kraigandrews
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Homework Statement


Q1-----Q2-----Q3; Q1=1.78E-6C;Q2=Q3=-Q1, r1=r2=1.82m
Calculate the total force on Q2. Give your answer with a positive number for a force directed to the right.



Homework Equations



F= kq1q2/r^2

The Attempt at a Solution


F2 = F12+F23
F12 = k(1.78E-6)(-1.78E-6)/(1.82^2)
F23 = k(-1.78E-6)(-1.78E-6)/(1.82^2)
The problem is these forces cancel and I know that they shouldn't, so I am sure is some thing I am just not seeing here.
 
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F12 is attractive, so it's in what direction?

F32 is repulsive, so it's in what direction?
 
F12 is negative so to the right and F32 is positive so it is to the right because Q2 is negative
 
kraigandrews said:
F12 is negative so to the right and F32 is positive so it is to the right because Q2 is negative
Therefore, they don't cancel !

Usually right is positive.
 
okay so then I am not sure where I am going wrong since I know that it shouldn't cancel the charges and the distances are the same for F12 and F32 so it should be 2*F12 = F2, I am not sure what I am doing wrong here this shouuld be a fairly simple problem.
 
The sign given by these two equations really only is useful in showing whether you have attraction (negative sign) or you have repulsion (positive sign).
F1,2 = k(1.78E-6)(-1.78E-6)/(1.822)

F2,3 = k(-1.78E-6)(-1.78E-6)/(1.822)​
You can't blindly add the results together.

Since each force is in the positive x direction, they are both positive and should be added together.
 

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