1. The problem statement, all variables and given/known data I am doing a lab experiment and the objective is to find the efficiency of an elastic band. Distance to ceiling=2.9m Mass of elastic band= 1.85g Force 2.6N (found using Newton meter) Extension: 6.4cm 2. Relevant equations Well I am not looking for a solution, I just need the way to setup the formulas in order to find efficiency. F1=-kx (Hooke's Law) F2=ma 3. The attempt at a solution I think that I should compare the force stored in the elastic band as mechanical energy to the force required to make the rubber band hit the ceiling. so I'd do this: -kx=ma Problem is that I don't know if acceleration should be taken to be gravity. Once I find acceleration, I should be able to find the initial velocity. Then, couldn't I use the work-energy theorem to compare the theoretical initial velocity to the actual velocity? Meaning, I compare the initial velocity I get when I use mgh=1/2mv^2 to the velocity I get when using acceleration. Sorry maybe what I said above is completely wrong. Please help, I was missing from class when the teacher went over it.