Question

A bus travels at $ v\text{ km/hr} $ . It is going from Daspur to Beespur. After the bus has travelled 5 hours, Beespur is still 20 km away. What is the distance from Despur to Beespur? Express it using $ v $ .

Answer 1

Hint: As it is given that the bus has travelled 5 hours at the speed of $ v\text{ km/hr} $ , we can say that the distance travelled in this 5 hours is $ 5v\text{ km} $ . Also, it is given that after the 5 hours of travel Beespur is still 20 km away, so add 20 km to the distance travelled in 5 hours to get the answer.

Complete step-by-step answer:
Let us start the solution to the above question by finding the distance travelled by the bus in the 5 hours, given that it was traveling at a speed of $ v\text{ km/hr} $ during this period. We know that $ \text{distance}=\text{speed}\times \text{time} $ . So, the distance travelled in the period of the first 5 hours is equal to $ 5v\text{ km} $ .
Also, it is given that after the bus has travelled 5 hours, Beespur is still 20km away. So, we will add the distance travelled by the bus in 5 hours with 20km to find the total distance between the point where the bus started, i.e., Daspur and Beespur.
So, the distance between Daspur and Beespur is $ \left( 5v+20 \right)\text{km} $ .

Note: Remember the formula $ \text{distance}=\text{speed}\times \text{time} $ is only valid if and only if the acceleration of the object is zero, i.e., the speed of the object must be constant. If the acceleration is constant then you need to use the different equations of motion and if the acceleration is changing then the approach of instantaneous speed comes into play. Until and unless it is mentioned, consider the speed to be constant.