Finding the change in velocity from an acceleration vs time graph

[MattDutra123]

Homework Statement

The graph shows the variation with time t of the acceleration a of an object (graph attached).
What is the change in velocity of the object in the time interval 0 to 4s?

Homework Equations

a = v/t

The Attempt at a Solution

My initial answer was -8 m/s, by simply finding the area under the curve. However, the correct answer is 8 m/s (positive). I don't understand how acceleration could be decreasing if the velocity isn't. How can acceleration decrease when the velocity is increasing?

 

[Ray Vickson]

Homework Statement

The graph shows the variation with time t of the acceleration a of an object (graph attached).
What is the change in velocity of the object in the time interval 0 to 4s?

Homework Equations

a = v/t

The Attempt at a Solution

My initial answer was -8 m/s, by simply finding the area under the curve. However, the correct answer is 8 m/s (positive). I don't understand how acceleration could be decreasing if the velocity isn't. How can acceleration decrease when the velocity is increasing?

Acceleration = rate of change of velocity, so as long as acceleration is positive, the velocity is increasing. In this case, the rate at which velocity increases becomes less as time passes, but it is still positive.