How to determine direction of forces in free body diagrams?

[Yoriko]

For instance, in the below diagram:

[PLAIN]http://img101.imageshack.us/img101/3205/59914396.png

How do you know if the reaction force on the beam is in Direction A or B? How do you determine the correction direction?

 

[Redbelly98]

Welcome to Physics Forums.

Don't worry about getting the correct direction. Break up the reaction force into x and y components, and solve for the forces that way. If the x-component turns out to be positive (towards the right), then the correct direction is B. If the x-component is negative, then it's A.

 

[issacnewton]

yes, I agree with redbelly, don't bother about the direction now. since the movement of the beam is being prevented in x and y direction at the hinge, just show forces in x and y direction. then when you use stability conditions, you will get correct magnitude and the direction anyway

 

[Yoriko]

Welcome to Physics Forums.

Don't worry about getting the correct direction. Break up the reaction force into x and y components, and solve for the forces that way. If the x-component turns out to be positive (towards the right), then the correct direction is B. If the x-component is negative, then it's A.

Ok thanks!