I am supposed to find the moment of the force at A about point O. Why do I keep getting zero, this can't be right. Where did I goof.
work.pdf
Thanks
I can't tell you where you went wrong, sorry. I wanted to say though that I looked over your work and all of your math looks good to me. Assuming you have the right $\displaystyle R_{ab}$, you did the right calculation for the unit vector. Your determinant calculation looks good to. So by my great powers of deduction it looks like your problem occurred determining the position or force vector. Hope this helps eliminate some doubt.