Instantaneous Velocity with Position v. Time graph

[achibaby1974]

Homework Statement

The position v. time graph for a certain object moving along the x-axis is shown.

I don't have the graph. Bu I have the points.

(0,-2), (1,9), (4,4), (6,4), (8,-4), (9,0)


The object's initial position is -2m. Find the instantaneous velocity at ... (m/s)
a.) 0.5s
b.) 2.5s
c.) 5 s
d.) 8.5 s

Homework Equations

I think ...

Instantaneous Velocity = (Xf - Xi) / (Tf - Ti)

The Attempt at a Solution

Well, I really don't understand where to start. Looking at the graph, for 0.5 sec ... I put 4. That was incorrect.

I put in (4-(-2)) / (0.5 - 0) = 6/0.5 = 12. That's incorrect as well.

I think I really don't understand the correct thing to do. If someone could give me some guidance or direction as how to tackle this I'd appreciate it. Thanks in advance!

 

[daveb]

The first thing you need to do is realize for each ordered pair (a,b) which value is position and which is time?