# Electric Force Vector Problem

1. Jul 26, 2012

### Manodesi524

1. The problem statement, all variables and given/known data

http://postimage.org/image/y4h1ubp8b/ [Broken]

2. Relevant equations

F_xy=(k*q*q)/r^2

3. The attempt at a solution

This is a problem involving Electric Force:

http://postimage.org/image/y4h1ubp8b/ [Broken]

My goal is to find the direction and magnitude of q1. However, every time i do it, i get .04 N @ 189 degrees when our teacher says it is 262.

I am also confused about what angle i should use when finding the components on q1 and q3. Is it 64 degrees or 26 degrees? Can someone show me what angle i should use and why?

I have a big exam tommorow and i am very stressed. I'd love an answer.

The Forces are as follows: F12=.054, F13=.014, F23= .11

Here is some work: sin(26.6)*.014= .006, which is x component of vector

cos(26.6) *.014- .054=-.41, which is my y component

I do phythag to get my force, which is .41 Newtons.

When I do inverse tangent of .006/.041, i get 8 degrees. I add this to 180 to get a final answer of 188. My teacher said its near 262. What did i do???????
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 6, 2017
2. Jul 26, 2012

### SammyS

Staff Emeritus
Do you mean 262 N, or 262° ?

q1 doesn't have a direction.

Do you mean the direction of the force on q1?

Last edited by a moderator: May 6, 2017
3. Jul 26, 2012

### VantagePoint72

You've calculated the magnitude of the force correctly: it is indeed 0.04 Newtons (mind your significant figures!). You haven't shown which angle you're labeling with 26.6 degrees, but your components are correct (with the exception of the missing zero in your y-component). Thus, $arctan(0.041N/0.006N) = 81.7^{\circ}$, or the vector points 82 degrees counter-clockwise from west. If you're measuring counter-clockwise from east (as I suppose your teacher is), you get 180 degrees + 82 degrees = 262 degrees. So, it appears you just got your opposite and your adjacent components backwards.