Solving a Statics Problem with F=80N

[ebinesos]

hey all. I'm having problems with what should be a simple statics problem.

"The Magnitude of force F is 80.0 N. What are the madnitude of its components a) F\ab and b) F\ac that are parallel to the bars AB and AC respectively."

The picture: Force F pointing straight down. bar AB pointing 30 left of straight up (NW), and and bar AC pointing 70 degrees left of straight up (NW also).

I know i need to use the dot product somehwhere, but I can't determine what i need to do it with respect to. But I did rotate the problem 90 degrees CCW, and had the resulting equation:

|80*F\ac|cos110 + |80*F\ab|cos150=0

additional question: will F\ab + F\ac = 80. When adding up all those forces this problem doesn't seem to be in static equallibrium...

Thanks

 

[haynewp]

No, adding the force onto each bar will not equal the original force.

Each component part of your equation is right, but I do not understand why you are trying to add the components. When you see a force written as F=#i+#j, the 'i' and 'j' are 90 degrees apart.