Forces on a Truss

(Today’s student guest is Erik Lundvall.)

…

This problem pertains to construction and the way a given force acts upon a given structure. Trusses are triangular pieces used in the construction of some buildings to support weight of other objects such as the weight of the roof for example. In this particular problem the truss extends from the side of the building and is used to support an object. Say you have a business and over the entrance you have a pretty good sized sign advertising your business. The sign sits on a truss that extends over the sidewalk.

If the downward force of the sign towards the building is 250 pounds, the angle of the truss between lines A and B is 20 degrees, and the angle between line A and the sign is 120 degrees, what is the amount of force in pounds that is pulling down on the truss?