I'm doing a Assignment is to conststruce a captapult that will launch a marshmallow(Large size) at target on the floor at the other end of the classroom. I designed catapult. the rules saing the energy;; to launch the marshmallow cannot come directly from the motion of a human being.so i used elastic band . but, they saing to calculate the distance. so, i use an enegy approach. so I determine the angle at which the mashmallow leaves the catapult.then I assume then energy loss of the arm is gained by the marshmallow.but I ued elastic band, but, i dont know how to measure the load distance to find the energy stored in the elaastic band.how to i take into this measure ments...coz, I dont know the formula of the elasticband energy stored. just i used this formula to find the velocity. Mgh = 1/2*M*V^2 but I dont consider the elastice band energy please any one could me help to solve this probelm I need the full foumula how to fine the calculation... pls sent me to email@example.com Thanks for look through my post.