Simple Harmonic Motion - position

[jalamb90]

Homework Statement

A 100 g ball attached to a spring with spring constant 2.9 oscillates horizontally on a frictionless table. Its velocity is 20 cm/s when x = 4.8 cm.

What is the ball's maximum acceleration?
which I found to be amax= 180 cm/s^2

What is the ball's position when the acceleration is maximum?

Homework Equations

x(t)= Acos(ωt)
x(t)= Acos(2pift)

The Attempt at a Solution

 

[rock.freak667]

Well at what time t is the acceleration maximum?