How do I show the 100N force is cartesian form?

[suspenc3]

Homework Statement

See attachment, I am getting everyone of these problems wrong.

Homework Equations

$$M_y = u_y(r_y X F)$$

Where u=unit vector defining the direction of y axis
r=distance from y-axis to any point on the line of action of F
F=acting force

The Attempt at a Solution

I think I am going wrong right from the beginning, how do I show the 100N force is cartesian form? What I am doing is :

A=1.2i+0j+0k
B=0.6i+0.6j+1.2k

$$AB =\frac{ -0.6i+0.6j+1.2k}{\sqrt{0.6^2+0.6^2+1.2^2}}$$

$$F_{AB} = (100N)\frac{ -0.6i+0.6j+1.2k}{\sqrt{0.6^2+0.6^2+1.2^2}}$$

Im not going to bother to post the rest since I am pretty sure this isn't how to do this.

Thanks

 

[suspenc3]

anyone?

 

[teknodude]

Well there's a few ways you can do this. The easiest is to take a moment about the y-axis. You have the force in vector form now, so in your diagram you can redraw that force in the x,y,z direction. Then use the right-hand rule to decide which forces produce moments about the y-axis.