Question

The speed of a bus is 72 km/h whereas the speed of a car is 125 m/s. Which vehicle moves faster?

Answer 1

Hint: Here, we will proceed by converting the given speed of the bus in km/h into the speed of the bus in m/s. This will help in comparing the speed of the bus with the speed of the car (which is only possible if both have the same units).

Complete step-by-step answer:

Formula Used- Speed in m/s = ${\displaystyle \frac{5}{18}}$(Speed in km/h).
Given, Speed of a bus = 72 km/hr
Speed of a car = 125 m/s

Here, we have to find which one of the following vehicles moves faster. This comparison can only be done if the units of speed of the car and the bus both are the same.
As we know that in order to convert the units of speed given in km/h to a speed whose units will be m/s we will multiply the value of the speed whose units are km/h with ${\displaystyle \frac{5}{18}}$.
Since, we are given the speed of the bus having unit km/h. We will multiply the value of the speed of bus with ${\displaystyle \frac{5}{18}}$ to get the speed of the bus bearing units m/s

i.e., Speed of bus in m/s = ${\displaystyle \frac{5}{18}}$(Speed of bus in km/h)

By substituting Speed of bus in km/h = 72 km/h in the above equation, we get
$\Rightarrow$ Speed of bus in m/s = ${\displaystyle \frac{5}{18}}$(72) = 5(4) = 20 m/s
So, the speed of the bus in m/s units is 20 m/s
Since, the speed of the car in m/s units is 125 m/s
Clearly, 125>20
Speed of the car in m/s > Speed of the bus in m/s

Therefore, the speed of the car is greater than the speed of the bus. This means that the vehicle which moves faster is a car not a bus.

Note: In this particular problem, we can also convert the units of the speed of the car from m/s to km/h. This can be done by multiplying the value of the speed of the car in m/s with ${\displaystyle \frac{18}{5}}$. This will give, Speed of the car in km/h = ${\displaystyle \frac{18}{5}}$(Speed of the car in m/s) = ${\displaystyle \frac{18}{5}}$(125) = 18(25) = 450 km/h. Clearly, the speed of the car in km/h is greater than 72 km/hr which is the speed of the bus in km/h.