[SOLVED] Simple Harmonic Motion This is the question I was given on my assignment, I can't seem to get it, bad prof so I am trying to teach all of this to myself, but this stuff is a bit confusing. From what I have tried and gather from examples in mt text, sub in .120s and solve but that is not working. The position of a mass that is oscillating on a spring is given by (14.0cm)cos[(18.0s^-1)t]. What is the speed of the mass when t = 0.120 s? Also, I don't think 18.0s^-1 is angular speed, I think its frequency but the book has nothing in it about it, got that from google. I am looking for a step in the right direction in solving this one, the equation I am using are: v = -wAsin(wt + theta) The solution I am getting is -13.4 m/s which is not right, any help would be great. Thanks.