Question

A bus decreases its speed from 80 km/h in 5s find acceleration of the bus

Answer 1

Initial velocity(u)=80 km/h

=5/18 m/s = 1km/h

80km/h=80 x 5/18=22.22m/s

Final velolity (v)=60km/h

=5/18m/s=1km/h

60km/h=60 x 5/18=16.66m/s

t=5s

a=v-u/t

a=16.66-22.22/5

=12.216 m/s2

Answer 2

The question isn't clear to me. The bus decreased its speed from 80 km/h to what? 60 km/h as you wrote? Or is that supposed to mean that it decreased its speed BY 80km/h?

If it went from 80km/h to 60km/h then the difference in velocity is 20km/h:
\[\frac{20km}{1hr}=\frac{20000m}{3600s}=5.56m/s\]\[a=\frac{\Delta V}{t}=\frac{-5.56m/s}{5s}=-1.11m/s^2\]
If it decreased its speed BY 80 km/h the difference in velocity is obviously 80km/h:
\[\frac{80km}{1hr}=\frac{80000m}{3600s}=22.22m/s\]\[a=\frac{\Delta V}{t}=\frac{-22.22m/s}{5s}=-4.444m/s^2\]

Answer 3

Don't forget to adjust for significant digits as well