# A car travels up a hill at the constant speed of 40 km/h and returns down the hill at the speed of 60 km/h. Calculate the average speed for the round trip.

7 years ago
Let us assume that the distance travelled by the car in travelling up or down the hill is s. Let the time taken by the car to travel up the hill with speed v1 is t1 whereas the time taken by the car to travel down the hill with speed v2 is t2.
Given:
Speed with which car travels up the hill, v1 = 40 km/h vl
Speed with which car travels down the hill, v2 = 60 km / h
The average speed of the car for the round trip is given as:

The total distance travelled by the car in a round trip is twice the distance it travelled up or down the hill that is 2s.

….….….….….….….…...(1)
The elapsed time for the round trip is the sum of the time (t1) taken to travel up the hill and time (t2) to travel down the hill. Therefore the average speed is given as:
Also the time t1 is given as:

The time t2 is given as:

Substitute the value of t1 and t2 in equation (1) to get:

Substitute the given values of v1 and v2 to get the average speed of round trip as:

Therefore the average speed of the car for the round trip is. 48 km/h.
2 years ago
Dear student,

Let the distance between two ends be ‘s’ and the time for the forward and return journey be t1 and t2 respectively.
Hence, average speed = 2(40)(60) / [40 + 60]
= 48 km/h

Hope it helps.
Thanks and regards,
Kushagra