1. The problem statement, all variables and given/known data A mass is oscillating on a spring with a period of 4.85 s. At t = 0 the mass has zero speed and is at x = 9.90 cm. What is the magnitude of the acceleration at t = 1.40 s? 2. Relevant equations a=-w2x x(t)=Acos(wt+phi) 3. The attempt at a solution I tried using the equation for acceleration by solving for w in the equation dealing with position, but I don't have the phase change constant, and otherwise I have no idea how to begin going about this problem. I need a push in the right direction!