The displacement of an object oscillating on a spring is given by: x(t)=A cos⁡(ωt+φ). At t = 0, the block starts at x = A/3 and moves to the right. The phase constant, φ, is

Answer 1

x(t)=A cos⁡(ωt+φ)
at t = 0, x = A/3 so
A/3 = A cos⁡(φ)
cos⁡(φ) = 1/3
φ = 1.23 radians or -1.23 radians
make sure the velocity is to the right (
dx/dt = - Aω sin⁡(ωt+φ)
at t = 0
dx/dt = - Aω sin⁡(φ)
better use the negative one if it is going right :)