1. The problem statement, all variables and given/known data How do i prove 0.5kx2=elastic energy? 2. Relevant equations 0.5kx2=elastic energy Energy in= Energy out 3. The attempt at a solution I understand how to use the formula but what i dont understand is where the formula comes from. I am guessing it has to do with Fx=Kx but am unsure how K=F then.