Question

A bus travels with 54kmph for first 20min and 72 kmph for next 20min.


Find the averagespeed of the bus

Answer 1

Answer:

63 kmph

Explanation:

       Using:   Distance = speed * time

Case 1: car travels with 54 kmph for first 20min.  

  Given, time = 20min = (1/3) hr

          ∴ Distance = (54)(1/3) km

                             = 18 km

                   

Case 2: car travels with 72 kmph for next 20min.  

  Given, time = 20min = (1/3) hr

          ∴ Distance = (72)(1/3) km

                             = 24 km

 From both the cases,

          total time = 1/3 + 1/3 hr

                           = 2/3 hr

       total distance = 18 + 24 km

                               = 42 km

∴ Average speed = distance/time

                     = 42/(2/3)  kmph

                     = (42*3)/2 kmph  

                     =  63 kmph

Answer 2

Given :-

A bus travels with 54kmph for first 20min and 72 kmph for next 20min.

To Find : -

The Average speed of bus

Solution :-

We know that

1 min = 60 sec

20 min = 20(60) = 1200 sec

54 km/h = 54 × 5/18 = 15 m/s

72 km/h = 72 × 5/18 = 20 m/s

We know that

Time = Distance/Speed

Distance = Speed × Time

Distance = 15 × 1200

Distance = 18000 m

Distance = Speed × Time

Distance = 20 × 1200

Distance = 24000 m

Now

Avg. Speed = Total distance/Total time

Avg. Speed = 24000 + 18000/1200 + 1200

Avg. Speed = 42000/2400

Avg. Speed = 420/24

Avg. Speed = 17.5 m/s