Hi all. I've this problem and I'm stuck on the part where I have to find the total energy. 1. The problem statement, all variables and given/known data A 507 g mass oscillates with an amplitude of 10 cm on a spring whose spring constant is 20 N/m. At t =0s the mass is 5.0 cm to the right of the equilibrium position and moving to the right. 2. Relevant equations E = K + U = (1/2)mvx^2 + (1/2)kx^2 I've already figured out the period to be 1.00s, the angular frequency is 6.28 rad/s, phase constant is -1.05 rad, initial velocity is .544 m/s, and final is .628 m/s. I know all of these to be correct. 3. The attempt at a solution Using the equation above and plugging numbers in I get: (1/2)(.507kg)(.544^2) + (1/2)(20Nm)(5.0cm^2) = 250.075J but this online homework thing says it's wrong. Should I use E = (1/2)m*vmax^2? That only gives .09J. Anybody have any clue? Thanks a lot!