A spitball traveling across a classroom slows down by air resistance by 9 m/s in 2 seconds. What was the acceleration of the spitball?

Answer 1

acceleration = (change in velocity) / (change in time)

1. change in velocity = -9 m/s. It's negative because its slowing down
2. change in time = 2 sec

a = (-9 m/s)/(2 s) = ____? m/s²