Question

Method Required

A man walks on a straight road from his home to market 2.5km away with a speed of 5km/hr. Finding the Market closed, he instantly turns and walks back home with a speed of 7.5km/h. The average speed of Man over the interval of time 0 to 40 min is equal to what ?

Answer 1

Heya........!!!!!

➡Let t1 be time taken from home to market = t1 = 2.5/5 = 30 min = 1/2 hr .

➡ Let t2 be the time taken from market to home = t2 = 2.5/7.5 = 1/3 h = 20 min.

So ,, Total time ( T ) = 30 + 20 = 50 min ( no need to calculate total time )

Now ,, average speed of man in interval of ( 0 - 40 min ) =>

➡Speed of the man = 7.5 km/h
➡Distance travelled in first 30 min = 2.5 km ( from first step )

As we have to take out average speed in interval of 0 - 40 min and we have the distance traveled in first 30 min , SO ,, let us take out the distance traveled in next 10 min

➡ = 7.5 × 10/60 = 1.25 km .

Total Distance = 1.25 + 2.5 = 3.75 km

Now average speed = D/T

here D = 3.75 Km/hr ,, T = 40 min = 40/60 hr .

♦Average speed V = 3.75 / (40/60) = 5.625 km/h


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