Question

A bus decreases its speed from $80{\mathrm{kmh}}^{-1}$ to $60{\mathrm{kmh}}^{-1}$ in $5\mathrm{s}$. Find the acceleration of the bus.

Answer 1

Step 1: Given data:

Initial velocity $u=80km/h=\left(80\times \frac{5}{18}\right)=22.2m/s$

Final velocity $v=60km/h=\left(60\times \frac{5}{18}\right)=16.7m/s$

Time $t=5s$

Step 2: Using the first motion equation for determining the value of acceleration

From the first motion equation, we have,$v=u+at$

Where, $u$ is initial velocity

$v$ is the final velocity

$a$ is acceleration

$t$ is the time period

So, the value of the acceleration will be,

$$\begin{gathered} a=\frac{v–u}{t} \\ \Rightarrow a=\frac{16.7–22.2}{5} \\ \Rightarrow a=\frac{-5.5}{5} \\ \Rightarrow a=-1.1m/s^2 \end{gathered}$$

Hence, the value of the acceleration will be $a=-1.1m/s^2$.