A spring with spring constant 190 N/m vibrates with an amplitude of 8.0 cm when 0.380 kg hangs from it.(adsbygoogle = window.adsbygoogle || []).push({});

What is the equation describing this motion as a function of time?

Assume the mass passes through the equilibrium point, toward positive x (upward), at t = 0.100 s.

x=A*cos(omega*t + phi)

I figured out that A is 8.0 cm, and omega is 22.36

but I can't figure out phi.

Here's what I did:

x=0 (because it's at equalibrium at .100 s)

Plug in numbers and get

0=A*cos(22.36*.100 + phi)

0/A = cos(22.36*.100 + phi)

arcosine(0) = 22.36*.100 + phi

phi = arcosine(0) - (22.36*.100)

What am I doing wrong?

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# Homework Help: Harmonic motion

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