# Force vectors

The three concurrent forces acting on the post produce a resultant force of 0. If F2 = 0.5F1, and F1 is to be 90 degrees from F2 as shown, determine the required magnitude F3 expressed in terms of F1 and the angle theta.

I am having no troubles finding the magnitude of F3, however, I am having trouble understanding how to get theta. Apparently the angle formed by F1 and F2, plus ninety degress, gives you the answer. However, I'm not seeing the relationship. Help? Related Introductory Physics Homework Help News on Phys.org
Doc Al
Mentor
Use theta to find the angle that F2 (and F1) makes with the horizontal.

Wouldnt you want to find the angle that F2 (and F1) makes with the vertical, then add 90 degrees to find theta?

Doc Al
Mentor
Wouldnt you want to find the angle that F2 (and F1) makes with the vertical, then add 90 degrees to find theta?
That also would work. Give it a try.

Express the angle that F1 and F2 make with the vertical or the horizontal in terms of theta. Then you can solve for theta.

For the vectors to cancel out, the combination of F1 and F2 must result in a vector having the same magnitude as F3 but having opposite direction.

So, to start, find the x-components of F1 and F2. Add them together to get the magnitude of F3. Then substitute what you know about the angles.