Question

A train covers 120 m in 5 seconds. What is the speed of the train in km/hr?

Answer 1

Hint: Here we go through by first finding the speed by the formula of speed i.e. ${\text{speed = }}\dfrac{{{\text{distance}}}}{{{\text{time}}}}$ and then use metric conversion to convert the answer in that unit in which the question asked.

Complete step-by-step answer:
Here in the question it is given that a train covers 120 m in 5 seconds. It means that distance travelled is 120m and the time taken is 5 second.
Distance= 120 m
Time= 5 second
And we know that ${\text{speed = }}\dfrac{{{\text{distance}}}}{{{\text{time}}}}$ put the value in the formula to find out the speed.
${\text{speed = }}\dfrac{{120m}}{{5s}} = 24\dfrac{m}{s}$
Here we find the speed that is 24 m/s.
Now we have to convert this speed into km/hr.
As we know that $1m = \dfrac{1}{{1000}}km$ and $1s = \dfrac{1}{{3600}}hr$
Now for converting 24m/s into km/hr. we first convert 24 m into km by multiplying $\dfrac{1}{{1000}}$into it and multiply $\dfrac{1}{{3600}}$ to second to convert it into hours.
It will be written as $ = \dfrac{{24 \times \dfrac{1}{{1000}}km}}{{1 \times \dfrac{1}{{3600}}hr}} = \dfrac{{24 \times 3600}}{{1000}} = 24 \times \dfrac{{18}}{5} = 86.5\dfrac{{km}}{{hr}}$
Hence the speed of the train is 86.5 km/hr.

Note: Whenever we face such types of problems we use some important points. Like we use that relation of metric conversions in which a required unit comes then apply that relation we convert one unit into another unit. In such questions we also use short tricks like for converting m/s to km/hr. we multiply it by $\dfrac{{18}}{5}$ and for converting km/hr. to m/s we multiply it by $\dfrac{5}{{18}}$.