Acceleration = (change in speed) / (time for the change)
-- during the first second, the object increases its speed to
(5 m/s²) · (1 s) = 5 m/s .
-- During the next 2 seconds, the object increases its speed by
(2 m/s²) · ( s) = 4 m/s
So at the end of the whole 3 seconds, its speed is (5 m/s) + (4 m/s) = 9 m/s
-- Over the whole time, its speed has changed from zero to 9 m/s.
Acceleration = (change in speed) / (time for the change)
Acceleration = (9 m/s) / (3 sec)
Acceleration = 3 m/s²
