# Addition of a System of Coplanar Forces

1. Sep 15, 2010

### tophernuts

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

The resultant force acting is directed along the positive x-axis, determine the magnitudes of F2 and the resultant force

And that F3x=4 and that F3y=3 (its a right angle 3-4-5 triangle)

2. Relevant equations
F1=F1x +F1Y
F2=F2x +F2Y
F3=F3x +F3Y

3. The attempt at a solution
F1y= 4cos(30) = 3.464
F3y=3

And since the resultant force is along the x-axis, the resultant y force (Fry) would therefore have to equal 0.

But when you run the numbers:

Fry=F1Y+F2Y+F3Y
Fry=(+3.464)N + (-3)N + F2y
F2y= -0.464
xsin30=-0.464
x=-0.464/sin30
x=-0.928

But that is impossible because F2 is above the x-axis and therefore couldn't have a negative y value.

This is where I am currently stuck, if it would work out i could figure out the resultant of F2y and F2x which would be F2, and the find out the resultant of all three from there on.

Chris

2. Sep 15, 2010

### cepheid

Staff Emeritus
Welcome to PF,

How do you know that F3 is 30 degrees from the x-axis? Your diagram doesn't indicate such.

3. Sep 16, 2010

### tophernuts

I don't, I just know that it is a 3-4-5 triangle.

I know that F2 is 30 degrees away from the x-axis though

4. Sep 16, 2010

### tophernuts

Well, this is embarrassing.
My friend who I was working on it with and I both failed to see the direction of the arrow F1...
As it is pointing downwards, not upwards, this question makes a lot more sense now...