A runner’s velocity along a straight track is 3.2 m/s at time 5.0 s and 2.2 m/s at time 13 s. Find the runner’s average acceleration during this time interval.
a = (Vf - Vo) / (Tf - To),
a = (2.2 - 3.2) / (13 - 5),
= -1 / 8 = -0.125 m/s^2.
The neg sign means that the runner was actually slowing down or decelerating.