Spring oscillator starting from rest at maximum displacement

[Bob Loblaw]

Homework Statement

A 171 g object on a spring oscillates left to right on a frictionless surface with a frequency of 3.00 Hz and an amplitude of 11.0 cm.
(a) What is the spring constant?
N/m
(b) If the object starts from rest at x = 11.0 cm at t = 0 and the equilibrium point is at x = 0, what equation describes its position (in centimeters) as a function of time (in seconds)?
x(t) =

Homework Equations

(a) was solved and the spring constant was found to be 60.75 N/m

(b) b) x = A cos (omega t)

The Attempt at a Solution

omega is 2pi*3 hZ so omega would be 6pi. Thusly, x(t) = .11 cos (6pi) t
Am I correct? Our online homework system is not accepting my answer and I am not certain if it is because I made a mistake in physics or the syntax of my answer. Could someone verify I am right or wrong?

 

[jincy34]

you need to add phase constant to your equation.

 

[Bob Loblaw]

I got it.

I needed to multiply out 6*pi to get its numerical value 18.85 and enclose the argument of the cosine function in parenthesis. 11cos(18.85t) worked.