Question

A car travels $36\text{km}$ in $2$ hours. Its average speed in ${\text{m s}}^{-1}$ is

• A. 5

Answer 1

The correct option is A 5
Average speed = Distance travelled / Time taken
$=\frac{36}{2}\text{kmph}$

$=18\text{kmph}$

The speed is in $\text{kmph}$. In order to convert it to ${\text{m s}}^{-1}$, we need to convert the units of distance and time

$18\text{kmph}=\frac{18\text{km}}{1\text{hr}}$

$=\frac{18\times 1000\text{m}}{1\times 60\times 60\text{s}}$

$=\frac{18\times 1000}{3600}{\text{m s}}^{-1}$

$=5{\text{m s}}^{-1}$