The graph above is for an object which is thrown vertically upwards with an initial velocity of 20 m/s. In the time period 0-2 seconds – the object decelerates from 20 m/s to 0 m/s.

On the graph of velocity vs. time, Δ v /Δ t is the slope of the curve. If the curve is straight, the acceleration is constant. If the curve isn't straight we have to do the same trick we did before ...