# Homework Help: Finding Electric Field at point P

1. Jan 29, 2012

### DrunkApple

1. The problem statement, all variables and given/known data
Two charges are located in the (x, y) plane as
shown. The fields produced by these charges
are observed at a point p with coordinates
(0, 0). Find the x-component of the electric field
at p. The value of the Coulomb constant is
8.98755 × 109 N · m$^{2}$/C$^{2}$.

2. Relevant equations
k$_{c}$ = 8.98755E9
cos θ$_{12}$ = $\frac{1.7}{sqrt(8.65)}$
cos θ$_{13}$ = $\frac{1.6}{sqrt(8.32)}$
q$_{2}$ = -8.1 C
q$_{3}$ = 7.9 C
r$_{12}$ = $sqrt(8.65)$
r$_{13}$ = $sqrt(8.32)$

3. The attempt at a solution
E$_{x}$ = -(k$_{c}$|q$_{2}$|cos θ$_{12})/r_{12}^{2}$ - (k$_{c}$|q$_{3}$|cos θ$_{13}$)/r$_{13}$$^{2}$

= -k$_{c}$($\frac{8.1}{8.65}$ * $\frac{1.7}{sqrt(8.65)}$ + $\frac{7.9}{8.32}$ * $\frac{1.6}{sqrt(8.32)}$)

is this the right way to do it?

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Last edited: Jan 29, 2012
2. Jan 29, 2012

### rude man

Hard to say since you didn't show or describe the locations of the charges ...

3. Jan 29, 2012

### DrunkApple

sorry here is the picture

4. Jan 29, 2012

### SammyS

Staff Emeritus

Not quite alright.

Where are the angles, θ12 , θ13 ?