Question

How many minutes will it take for the car that is travelling $80\,miles\,h{{r}^{-1}}$ to travel $200km$?

Answer 1

Hint: Speed is the distance travelled by an object in one second or unit time. There are different units to express speed in different unit systems. The speed and distance travelled is given in the question. Substituting corresponding values in the formula for speed, we can calculate the time taken. Convert the unit of distance into kilometers and hence the unit of speed. Ultimately the answer must be minutes.
Formulas used:
$s=\dfrac{d}{t}$

Complete answer:
The speed of the body is the distance travelled in unit time. Its SI unit is $m{{s}^{-1}}$. Therefore,
$s=\dfrac{d}{t}$ - (1)
Here, $s$ is the speed of the body
$d$ is the distance travelled
$t$ is the time taken
Given, the speed of a car is $80\,miles\,h{{r}^{-1}}$, it travels $200km$
The relation between miles and kilometers is given as-
$1mile=1.61km$
Using the above equation we convert $80miles$ into kilometers, we get,
$\begin{align}
  & x\,km=80\times 1.61 \\
 & \Rightarrow x\,km=128.8km \\
\end{align}$
Therefore, the car travels $128.8km$ in one hour, hence its speed is $128.8km\,h{{r}^{-1}}$
We substitute given values in eq (1) to get,
$\begin{align}
  & 128.8=\dfrac{200}{t} \\
 & \Rightarrow t=\dfrac{200}{128.8} \\
 & \therefore t=1.55\,hours \\
\end{align}$
The time taken by the car to travel 200km is $1.55\,hours$. Time taken in minutes will be-$1.55\times 60\min s=93\text{mins}$
The time taken in minutes by the car to travel 200 km is $93\text{mins}$.

Note:
Speed is a scalar quantity, it describes the motion of an object in one dimension. The SI unit of time seconds, it is the one of the seven fundamental units in the SI system. Miles is a unit of length used in the English system, while a kilometer is a unit of length used in the MKS system. The SI system is the most commonly used system around the world.