Question

Example 1: During first half of a journey by abody it travel with a speed of 40 km/hr andin the next half it travels with a speed of 20
km/hr. Calculate the average speed of thewhole journey.
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Answer 1

let total distance is X m then in first half(X/2) speed is 40km/hr(40×5/18= 100/9m/sec) then let time in for this half is t1= X/2/100/9. , and another next half( X/2) speed is 20km/h(20×5/18=50/9m/sec) and for another half time is t2 =X/2/50/9 then av.speed = total distance/t1+t2 , av. speed=X/(X/2/100/9)+(X/2/50/9) then X is cancelled out then , av. speed= 1/(9/200)+(9/100)

av. speed= 1/(9+18/200), av. speed= 200/27 m/sec , 200/27×18/5= 26.67km/hr