The odometer of a car reads $2000\mathrm{km}$ at the start of a trip and $2400\mathrm{km}$ at the end of the trip. If the trip took $8\mathrm{h}$, calculate the average speed of the car in $\mathrm{km}{\mathrm{h}}^{-1}$ and $\mathrm{m}{\mathrm{s}}^{-1}$.

Step1: Given Data

Distance traveled in $8\mathrm{h}$ will be $2400-2000=400\mathrm{km}$.

Step2: Average Speed

The average speed of the car = $\frac{\mathrm{total}\mathrm{distance}\mathrm{travelled}}{\mathrm{total}\mathrm{time}\mathrm{taken}}$.

$\therefore$ average speed of the car in $\mathrm{km}{\mathrm{h}}^{-1}$ = $\frac{400}{8}=50\mathrm{km}{\mathrm{h}}^{-1}$.

Average speed of car in $\mathrm{m}{\mathrm{s}}^{-1}$ = $50\times \frac{5}{18}=13.89\mathrm{m}{\mathrm{s}}^{-1}$.