Damped Oscillator and amplitude

[JohnnyCollins]

1. Homework Statement [/b]
Consider the damped oscillator illustrated in the figure below. Assume that the mass is 365g, the spring constant is 112N/m, and b = 0.117kg/s. How long does it take for the amplitude to drop to half its initial value? (A*e-b*t/(2m))


http://loncapa.physics.mun.ca/res/mun/PHYSICS/serway-calc/Graphics/Graph13/serb1370.gif

Homework Equations

ω=√ω_o^2-(b/2m)^2
ω_o=√k/m

The Attempt at a Solution

I solved for ω using the two of the above equations and got 17.5 rad/s
i just don't know where to go from here, any suggestions ?

 

[Spinnor]

From,

http://hyperphysics.phy-astr.gsu.edu/hbase/oscda.html

A general solution looks like x=... below,

Looks like you have no cos term?

You have to click it twice to see it properly?