Question

An airplane travels $900\;km$ at a speed of $150km/h$. How long did it take for the airplane to travel a distance of $900\;km$?

Answer 1

We know from the definition of speed, that speed is the ratio of total distance covered by the total time taken by the moving object. Here, the speed of the aeroplane and the distance covered by the aeroplane, during the constant speed is given and hence we can find the time taken by the aeroplane.
Formula used:
$s=\dfrac{d}{t}$

Complete answer:
We know that speed is a scalar quantity, which defines how fast or slow an object is moving with respect to the other. Also, speed $s$ is mathematically given as the ratio of the total distance covered $d$ by the moving object to the total time taken $t$ by the moving object is given as;
$s=\dfrac{d}{t}$
Here, given that the speed of the aeroplane, remains the same during the travel, and it is given as $s=150km/h$ . Also the total distance covered is given as $d=900m$. Then using the above formula, we have
$\implies t=\dfrac{d}{s}$
$\implies t=\dfrac{900}{150}$
$\implies t=6h$
Thus it will take $6\;hrs$ for the aeroplane to cover a distance of $900\;km$ at a speed of $150km/h$

Note:
There are two quantities, namely the velocity and speed which define how fast or slow an object is moving with respect to the other. The former is a vector, which has both direction and magnitude. While the latter is a scalar, which has only magnitude, and no direction. Also, the former is defined as the ratio of displacement to total time taken, while the latter is the ratio of the total distance covered to the total time taken.
Here, since the speed of the aeroplane remains constant during the travel, we use the average speed to calculate the time taken. But if the speed was varying, then we can use the instantaneous speed to calculate the time taken by the aeroplane.