Freebody diagram of a bridge, physics help

Heres the picture of my bridge :
http://i44.tinypic.com/2rztcif.jpg


1) I need help drawing the Freebody diagram of the bridge

2) Pretend there is a hole in the middle of the bridge and there is a metal hook there. At the bottom of the hook there is a mass of 1.3kg. I need help drawing the free-body diagram of this too

My bridge has a force of 2.7N so it weights around 296 g

What is the normal force exerted by each chair?

Thanks so much :)

Assuming your bridge wouldn't slide left or right no matter how slippery your chairs are, your bridge has three forces acting on it. There's a normal force upward from the chair on the left, a normal force upward from the chair on the right, and a gravitational force downward.

To draw a Free Body Diagram, represent the object of interest as a point. Each force acting on the object should be represented by an arrow with its tail on the point and pointing in the direction it acts. So your diagram will have two arrows upward representing the normal forces, and one arrow downward representing the gravitational force.

If your bridge is symmetrical, then each chair must exert a normal force equal to half the magnitude of the gravitational force. If your bridge is not symmetrical, then you are going to need to look at torques, and a Free Body Diagram won't be enough.

It isn't entirely clear what "this" is when you ask, "I need help drawing the free-body diagram of this too". The simplest "this" results from treating the bridge, hook, and hanging mass as one big object. (We can define our object of interest however we find convenient.) In that case, the FBD is exactly the same as it was for the bridge alone, but since the gravitational force will be greater, the normal forces will be greater, too.

If "this" is just the hanging mass, the FBD has a gravitational force downward and a tension upward. (These will have the same magnitude.)