Question

A bus decreases its speed from 80 km/h to 60km/h in 5s. Find the acceleration of the bus?

Answer 1

Step 1: Given data

1. The initial speed (u) of the bus is $80km/\mathrm{h}=80\times \left(\frac{5}{18}\right)=22.22\mathrm{m}/\mathrm{s}.$
2. The final speed (v) of the bus is $60\mathrm{km}/\mathrm{h}=60\times \left(\frac{5}{18}\right)=16.67\mathrm{m}/\mathrm{s}.$
3. Time (t) is 5 seconds.

Step 2: Finding the acceleration of the bus

By using the 1st equation of motion,

$\mathrm{v}=\mathrm{u}+\mathrm{at}$

Where, "v" and “u” are the final and initial velocities respectively, “a” is an acceleration, and “t” is time.

Putting the given values.

$$\begin{gathered} \Rightarrow 16.67=22.22+a\times 5 \\ \Rightarrow -5.55=a\times 5 \\ \Rightarrow a=-1.11m/s^2 \end{gathered}$$

The negative sign indicates that it is retardation.

Hence, the acceleration of the train will be -1.11 m/s².