Trouble with electric force question

AI Thread Summary
The discussion centers on a homework problem involving the calculation of the electric force vector on charge q3 due to charges q1 and q2. The user attempts to apply the formula for electric force and calculates the distances using the Pythagorean theorem, arriving at specific unit vectors for each force. However, the user realizes there may be an error in the distance calculation for q1, which affects the final result. Other participants suggest checking the distance for q1 to identify the mistake. The user expresses gratitude for the assistance and acknowledges the need for a fresh perspective on the problem.
con31773
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Homework Statement


I'm having a little trouble with an electric force question I have been working on. It seems simple, but my answer keeps coming out incorrect. Using the graph, deduce the electric force vector on charge q3 by q1/2. In case it is not clear, q3 lies on point (2,2)
Graph.jpg


Homework Equations



F=(kq1q2)/r^2*\hat{r}

The Attempt at a Solution


Okay, well since electric force vectors simply add to give resultant force I can deduced the individual vectors and sum, as such.

F(1/3)=(kq1q3)/r^2*\hat{r}(1/3)

and the same applies to the second charge

F(2/3)=(kq3q2)/r^2*\hat{r}(2/3)

then I deduced r for both. Simply being 2 for q(2/3), and 5 for q(1/3) (from pythagoras)
Then, the unit vectors, as (2\hat{i}+\hat{j})/5 for q(1/3)
and \hat{j} for q(2/3)

Put it together I got
F(1/3)=((kq1q3)/25)(2\hat{i}+\hat{j})

F(2/3)=((kq2q3)/4)\hat{j}

Evaluate and sum, I got, 0.367\hat{i}-0.412\hat{j}

which of course is not correct. I'm sure there is a mistake in there but can not find it. Would be greatful for some fresh eyes to tell me where.

Thank you in advance. :)
 
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Hello con31772 and welcome to PF!

con31773 said:
then I deduced r for both. Simply being 2 for q(2/3), and 5 for q(1/3)

Oops. Check what you got for r for q(1/3).
 
Oops. Check what you got for r for q(1/3)

Haha, thanks very much. Could not find my mistake at all.
 
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