A bus decreases its speed from 80 km h^-1 to 60 km h^-1 in 5 s. Find the acceleration of the bus.

Firstly, we will change the speed from km/h to m/s, as the given time is in seconds.

Initial speed, u = 80 km/h 

= 80 x 1000m/60 x 60s

=22.22 m/s(i)

Final speed of bus, v = 60 km/h

= 60 x 1000 m/60 x 60s

= 16.66 m/s(ii)

Time taken, t = 5s (iii)

As we know,

Acceleration, a = v-u/t

a = 16.66 - 22.22/5

a = -5.56/5

a = -1.11m/s²

Here, negative sign shows the negative acceleration of retardation.