A train travelled $720\text{ km}$ in $20$ hours. Find its speed.

Hint: We have been given that the distance a train travelled is $720\text{ km}$ in $20$ hours .To find speed use the formula $\text{speed=}\dfrac{\text{distance }}{\text{time}}$ . Try it, you will get the answer.

Complete step-by-step answer:
Speed is defined as the rate of change of position of an object in any direction.
It is measured as the ratio of distance to the time in which the distance was covered. Speed is a scalar quantity as it has only direction and no magnitude.

For the measurement of speed in vehicles, speedometers are used while for measuring the distance odometers are used. Speed can also be calculated with the help of graphs. Distance-time graphs help in understanding the speed of an object.

When we see some activities like a running boy, moving bus etc, only one question is put in our mind about how these things are moving. For this one word is motion in Physics. The concept of motion is described by using some terms like velocity, speed, distance; acceleration etc. motion is described as changing the position of moving objects at an instant of time or period time.

Speed is one of the basic parameters for motion. It is quite different with speed as it is not only covered in length or distance. It is a scalar quantity with only magnitude not direction. It was first discovered by Galileo. He gave the formula and definition of speed that is distance divided time.

Speed is a scalar quantity which means it has no direction. It denotes how fast an object is moving. If the speed of the particle is high it means the particle is moving fast and if it is low, it means the particle is moving slow.

Now it is given that a train travelled $720\text{ km}$ in $20$hours.
We know that, $\text{speed=}\dfrac{\text{distance }}{\text{time}}$ .
Speed $=\dfrac{720}{20}=36\text{ km per hour}$ .
So we get the speed of the train as $36\text{ km per hour}$ .

Note: Read the question carefully. Also, you must know the concept behind the speed. You should be familiar with the formulae. Do not make silly mistakes while simplifying. Solve the problem in a step by step manner.