A car travels from A to B at a velocity of 20 km/h and returns at a velocity of 30 km/h. The average speed of car for the whole journey is : a) 5km/h b) 0km/h c) 25km/h d) 24km/h
Answers
Average speed is defined as the ratio of total distance covered with respect to total time taken.
Case 1)
A car travels from A to B at a velocity of 20 km/h.
Let us assume that the distance covered by the car is 'x' km.
We know that,
Time = Distance/Speed
t1 = x/20 hr ...................(1st equation)
Case 2)
The car returns to A from B with a velocity of 30 km/hr.
t2 = x/30 ...................(2nd equation)
Total distance covered by car = Distance covered by car from A to B + Distance covered by the car from B to A
Since, in both the cases distance covered is same. As, the car returns back using the same pathway.
So, total distance covered by car is 2x km (x+x).
Total time taken by car = t1 + t2
= x/20 + x/30
= (3x + 2x)/60
= 5x/60
Average speed = (Total distance covered)/(Total time taken)
= 2x(5x/60)
= (2 × 60)/5
= 24 km/hr
Therefore, the average speed of the car is 24 km/hr.
Option d) 24 km/hr