Q24 of 47 Page 8

Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 30 km h-1. What is the average speed for Abdul’s trip?

Let us assume the school to be at distance x km from where Abdul starts

Suppose the time taken while driving to school is t1

Given,

Average speed = 20 km/h



Time taken,

On returning from the trip the average speed is 30 km/h

Let, the time taken for the return trip is t2



Time taken, 


Now, total distance of the whole trip from going to trip to returning back to school is:

Total distance = x + x

= 2x Km (3)

Adding (1) and (2) to get the total time

Total Time taken = Time taken to go to college +Time taken to return back to school



Solving this equation

=

=(4)


Now, we will calculate the average speed of the whole trip:

Average speed =

=


= 24 km/h


Therefore, the average speed for Abdul’s whole trip from going from to school to return back is 24 Km/h.

More from this chapter

All 47 →
22

A bus starting from rest moves with a uniform acceleration of 0.1 ms-2 for 2 minutes. Find:

(a) The speed acquired.


(b) The distance travelled.

 23

A stone is thrown in vertically upward direction with a velocity of 5 m s-1. If the acceleration of the stone during its motion is 10 m s-2 in the downward direction, what will be the height attained by the stone and how much time will it take to reach there?

 25

A driver of a car travelling at 52 km h-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?

 26

A car is moving on a straight road with a uniform acceleration. The following table gives the speed of the car at various instants of time.


(i) Draw the shape of speed-time graph representing the above sets of observations.


(ii)Find the acceleration of the car.