Cant get y-component of point charges on test charge

[mujadeo]

Homework Statement

Six point charges, four positive (+q) and two negative (-q), are fixed at thepositions shown (i attached a .gif file --pls tell me if this isn't visable) in the x-y plane; q = 2.1 × 10-6C and a = 0.93 m. A test charge Q = 0.6 × 10-6C is at the origin.

(a) Find the x- and y-components of the total force on Q:

Homework Equations

i successfully calcd the x-component (-.017016N) but can't get the y component

The Attempt at a Solution

heres what i did

1. labelled the charges A thru F starting with the charge on the neg y-axis (A) and the labelled in cw direction.

2. so for y component everything either cancels or has no y-component, EXCEPT for the 2 charges on the y-axis. These are both pos charges.
so here's the calc
Ay = (9*10^9)(2.1*10^-6)(.6*10-6) / (.93^2) = .01311N (pos charge)
Dy = (9*10^9)(2.1*10^-6)(.6*10-6) / (.93^2) = .01311N (also pos charge)
so 2(.01311) = .02622N
this is wrong!
please help!
thanks

 

[learningphysics]

2. so for y component everything either cancels or has no y-component, EXCEPT for the 2 charges on the y-axis.

No. this is wrong. The two charges on the y-axis exert equal but opposite forces on Q, hence they cancel.

Which are the two charges you need to consider?

 

[m2003]

I would suggest double-checking your calculations and making sure you are using the correct equations for calculating the force on a test charge due to multiple point charges. Additionally, it is important to take into account the direction of the forces and use vector addition to calculate the total force on the test charge. If you are still having trouble, I would recommend seeking help from a classmate, teacher, or tutor.