Question

A car travels a distance 2000m.if the first half distance is covered at 40km/h and the second half with speed v and average speed is 48km/h then the value of v is?

Answer 1

Total distance = 2000 m = 2 km

First half = 2km/2 = 1 km

Second half = 1 km

As, speed in first half = 40 kmph

so, time taken = 1/40 h

also, speed in second half = v kmph

so, time taken = 1/v h

As average speed = total distance/total time

and total time = 1/40 + 1/v = (v+40)/40v h

and average speed = 48 kmph

so, 48 = 2 /{(v+40)/40v} = 2×40v / (v+40)

=> 48 × (v+40) = 80v

=> 48v + 1920 = 80v

=> 32v = 1920

so, v = 1920/32 = 60 kmph.