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## Homework Statement

A 1.00-kg glider attached to a spring with a force constant 16.0 N/m oscillates on a frictionless, horizontal air track. At t = 0, the glider is released from rest at x = -2.50 cm (that is, the spring is compressed by 2.50 cm).

Find the position, velocity, and acceleration as functions of time. (Where position is in m, velocity is in m/s, acceleration is in m/s2, and t is in s. Use the following as necessary: t.)

## Homework Equations

x(t)=Acos(ωt+ φ)

v(t)= dx/dt

a(t)=d^2x/dt^2

ω=√(k/m)

## The Attempt at a Solution

I know that the answer is x(t)= .025cos(4t+π) (then taking the derivatives respectively). What I can't figure out however is why φ=π. I thought if the particle is at its maximum position (x=A) at t=0, φ=0?