Particle Angular Velocity Problem

[user3298]

Homework Statement

I am given this graph and asked to find:
a. the particle's angular velocity at t=1s
b. angular velocity at t=4s
c. angular velocity at t=7s

Homework Equations

ω = θ/t

The Attempt at a Solution

I got 0 for a, which is the correct answer. However, I cannot seem to figure out b or c. For c, I got 2π/7 and it is incorrect. I've also tried 2π*radians/T and that doesn't work either. I'm not really sure what to do.

 

[elegysix]

are you sure ω = θ/t is the right equation?

how do you find velocity on a graph of position vs time?