Question

A runner starts slowing down as she gets tired. At 10 seconds, she 8m/a, and slows down to 2m/a at 13 seconds. What is her acceleration.

Answer 1

Magnitude of acceleration = (change in speed) / (time for the change) .

Change in speed = (end speed) - (start speed)
= (2 m/a) - (8 m/a) = -6 m/a .

Time for the change = (end time) - (start time)
= (13 sec) - (10 sec) = 3 sec .

Magnitude of acceleration = (-6 m/a) / (3 sec)

= -2 m/a per second .

(That's the best I can do with the ambiguous units.
What unit of speed is 'm/a' ? Is that "miles per afternoon" ?)