Question

A car travels a certain distance with a speed of 40 m/s second and returns with a speed u if the average speed for the whole journey is 48 m/s what is the value of u?

Answer 1

Let Say one side Distance = S  m

Time for one side = S/40   sec

return speed = u m/s

return time = S/u  sec

Total time taken =  S/40  + S/u   sec

Total Distance covered = S + S = 2S  m

Average Speed = Total Distance / Total Time

48 = 2S / ( (S/40+S/u)

24 (S/40 + S/u) = S

24 (1/40 + 1/u) = 1

24*(1/40u)(u+40) = 1

24u + 24*40 = 40u

16u = 960

u = 60 m/s

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