Question

Is t =0 consider at rest ? (given the graph on the picture attached)
my book's solution only shows it is at rest at t = 2 and t=6
but i believe t=0 should also be at rest

Answer 1

no i think you don't count it at rest when you are just starting out. the derivative for example does not exist at that point

Answer 2

oh, so i just need to count the turning points?

Answer 3

and thanks :)