# Homework Help: Determining Force

1. Sep 24, 2008

### Eternal Sky

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

Two forces, Fa and Fb, act on an object located at the origin. Fa has a force of 4500 N and has an angle of 60 degrees with respect to the positive x-axis. Fb has an angle of 140 degrees with respect to the positive x-axis. Determine the force of Fb.

2. Relevant equations

Component vector equations (possibly):

sin θ = Vy/V

cos θ = Vx/V

tan θ = Vy/Vx

V^2 = Vx^2 + Vy^2

Newton's Second Law:

F = ma

3. The attempt at a solution

I split up Fa into it's components, but that didn't really help me to solve for Fb. I also had the idea of using the law of sines:

sin 140/4500 N = sin 60/b

However, the answer came out to 6062 N, and my textbook has the answer listed as 6890 N. Besides, my book doesn't even mention the law of sines, so this probably isn't the correct method.

Any help would be greatly appreciated.

2. Sep 24, 2008

### ||spoon||

It sounds as if (although you didnt mention it) that the box in in static equilibrium??

If this is true then the net force must be zero, decomposing the vectors into two directions (vertical & horizontal) should make this easier

-spoon

3. Sep 24, 2008

### Eternal Sky

That makes things a great deal easier. Thanks for your help!