Determine directions for 2 dimensional Force Systems

[kivine]

Homework Statement

Example 1
http://img143.imageshack.us/img143/6944/86439707.png
Example 2
http://img266.imageshack.us/img266/2154/ay2.png

Homework Equations

Non.

The Attempt at a Solution

For a smooth pin, there are 2 unknowns. Fx and Fy
Why does Ay (Fy) act in the -ve(down) direction, and sometimes in the up direction ^
I'm quite confused :grumpy:
Does the question got to do with the directions? I will post the question if needed to

 

[PhanthomJay]

The direction is dependent on satisfying the equilibrium equations where the sum of forces and moments about a point must equal zero. You can always assume a direction, and if you get a minus sign for your result, you assumed the wrong direction.

 

[kivine]

thanks alot. .