The problem statement, all variables and given/known data A mass is oscillating on a spring with a period of 4.35 s. At t = 0 the mass has zero speed and is at x = 3.25 cm. What is the magnitude of the acceleration at t = 1.30 s? The attempt at a solution The formula for oscillatory acceleration is a(t) = -Aω^2cos(ωt - ∅) a(x) = -(ω^2)x ω = 2pi/period, which is 2pi/4.35 So, a(t) = -(2pi/4.35)(3025cos((2pi/4.35)(1.30))) a(t) = 0.6798 m/s^2 This isn't the correct answer. The question states that it starts at t= 0 at x=3.25, so I took that to be A. Is that my problem? Where am I going wrong?