1. The problem statement, all variables and given/known data A 0.500 kg mass resting on a frictionless surface is attached to a horizontal spring with a spring constant of 45 N/m. When you are not looking, your lab partner pulls the mass to oneside and then releases it. When it passes the equilibrium position, its speed is 3.375 m/s. How far from the equilibrium position did your lab partner pull the mass before releasing it? 2. Relevant equations Ee = 0.5 * k * x^2 Ek = 0.5 * m * v^2 Energy is conserved within the system: Einitial = Efinal 3. The attempt at a solution At the equilibrium position, only kinetic energy is present. At the "unknown" position, there is elastic potential energy because the mass has strayed from the equilibrium ...but since we don't know if the mass has been pulled to the maximum distance, I'm not sure whether or not there is kinetic energy. I'm not going to include it in my calculation because otherwise I'll have two unknowns ("x" and "v2") Ek = Ee 0.5*m*v^2 = 0.5 * k * x^2 x = SQRT [ (m*v^2) / k ] x = SQRT [ (0.500*3.375^2) / 45) ] x = 0.36m The answer is actually 0.19 m. I think I probably set up my equation incorrectly. Could someone look it over please?