An automobile is moving in an easterly direction at a velocity of 100km/hr. He sees an emergency vehicle and slows down to 60 km/hour. If it takes him 5.0 seconds to slow down, what is his acceleration?

100 km/h = 27.78 m/s

60 km/h = 16.67 m/s
(delta V) = V2 - V1
= 16.67-27.78 = -11.11 m/s

acceleration = (V2 -V1)/t = -2.22 m/s^2