Simple harmonic motion equation

[jumptheair]

Homework Statement

An object is undergoing simple harmonic motion. The graph shows the position of the object as a function of time. What is the first time after t = 0 s when the speed reaches a maximum?

http://www.learning.physics.dal.ca/dalphysicslib/Graphics/Gtype26/shm.47.jpeg

Homework Equations

I don't know what equation to use to figure this out. φ = φo + wt perhaps?

The Attempt at a Solution

Im told that position at t=0 gives phi_0. But still do not know how to use the equation nor figure out any of the variables. Help is needed!

 

[rl.bhat]

From the graph we get the following information. At t = 0 x = 1.5 cm, maximum displacent = 3cm, and period = 2s.
Wright the equation of simple harmonic motion x = Asin(wt + phi). In this put A = 3cm, t = 0 and x = 1.5 cm find phi. Next take derivative of the equation, which gives the velocity and put it equal to zero. And find t.