How can I find the value of phi in a simple harmonic motion equation?

[ice87]

http://noether.physics.ubc.ca/physics153/assign72k5.pdf

I don't get number 1 c, which equation do i use? and in general, how would I be able to find phi?

OK, i figured i should find the first derivative of the displacement formula, which becomes v = -Asin(wt + phi) but that still undoable, how do i find phi?

 

[µ³]

Check your derivative. remember that max(sin(x)) is 1

 

[ice87]

ah yes, i see, it should be v = -A ωsin(ωt + φ), but that's just a typo, i actually had this equation when i wrote it down on paper. But i still don't know how to find phi

 

[lightgrav]

look at t=0 ... what's the function? what's the graph?
phi is just the "little wt offset" if you don't start the timer in synch.