Calculating Electric Force on a Charge

AI Thread Summary
To calculate the total electric force on charge Q2, the forces F12 and F23 must be considered, where F12 is the attractive force between Q1 and Q2, and F23 is the repulsive force between Q2 and Q3. Both forces are directed to the right, leading to a positive total force. The correct approach is to sum the magnitudes of these forces rather than blindly adding their calculated values. The misunderstanding lies in the interpretation of the signs; since both forces act in the same direction, they should be combined to find the total force on Q2. The final calculation confirms that the forces do not cancel and yield a net positive force directed to the right.
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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