initial speed of the bus (u) = 80km/h = 80 x 5/18
= 22.22 m/s
Final speed of the bus (v) = 60km/h = 60 x 5/18
Time taken to decrease the speed (t) = 5s
Acceleration of the bus (a) = v-u/t = 16.67-22.22/5 = -1.11 m/ second square.
Negative sign of the acceleration indicates that the velocity of the bus is decreasing.