1. The problem statement, all variables and given/known data What is the potential energy of the spring? mass=.52 kg velocity=-6.54sin(20.1t) time=40.84 seconds amplitude=.33 meters angular frequency=20.1 2. Relevant equations U =1/2kx2 3. The attempt at a solution I used x=Acos(wt) and got .2 meters for x. I know this is right.I don't know how to find k.