Ok we had to build a catapult for physics....

Its finally finsihed. But now that we have to do analysis we are stummped. We have 4 large springs atached to one end of the arm and the arm is on a pivot. Here is a picture...that illustrates it better:








What formula will I have to use to calculate the force exerted by the arm.

Complete pictures:
http://mykg4orce.fasthost.tv/pult_pics/index.html