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## Homework Statement

Here's the graph:

http://i.imgur.com/uUXPO.jpg

What is the average acceleration between t=0s and t=2s?

## Homework Equations

a avg = change in velocity / change in time ; (Vf-Vi)/(tf-ti)

## The Attempt at a Solution

I know how to solve it if it was just a straight line where I could just plug in the numbers into the formula, but how do I calculate the average acceleration if the section above is non-straight? The part I don't get exactly is how to calculate the change in velocity itself since it's decreasing from 0s to 1s and then increasing from 1s to 2s.

As I understand the acceleration in this problem is the slope?

I tried calculating the slopes of those intervals separately and then adding them together and dividing by the change in time (2s), but I seem to be getting the wrong answer because my homework is online and it tells me if the answer plugged in is correct or not.

0s to 1s interval contains points (0,4) and (1,2) so the slope is -2

1s to 2s interval contains points (1,2) and (2,3) so the slope is 1

then (-2)+1/2= -0.5 m/s^2 even without dividing and ending up with answer 1, the avg acceleration is still incorrect

So since I am doing this completely wrong can somebody explain to me the whole concept, because for some reason I just don't seem to get it