# Drawing Free Body Diagrams

theBEAST

## Homework Statement

Assume the system is massless.

## The Attempt at a Solution

Here is my quick attempt at drawing a free body diagram for this system:

What I am not sure about is the direction of the force at F. Should the force be A or B?

Staff Emeritus
Gold Member
Can't you just assume a direction, and if the force comes out negative, it's in the opposite direction from what you assumed?

theBEAST
Can't you just assume a direction, and if the force comes out negative, it's in the opposite direction from what you assumed?

The prof posted answers online and it says that F is a roller joint and there is no force in the x direction. The reason why it is a roller joint is because if it wasn't it would be over constrained. Does anyone understand what is meant by this?

Staff Emeritus
Gold Member
The prof posted answers online and it says that F is a roller joint and there is no force in the x direction. The reason why it is a roller joint is because if it wasn't it would be over constrained. Does anyone understand what is meant by this?

Hmm...try looking at this:

http://en.wikipedia.org/wiki/Overdetermined_system

Staff Emeritus