Question

# Two towns A and B are connected by a regular bus service with a bus leaving in either direction every T minutes. A man cycling with a speed of $$20km/h$$ in the direction A to B notices that a bus goes past him every $$18$$ min in the direction of his motion, and every $$6$$ min in the opposite direction. What is the period T of the bus service and with what speed (assumed constant) do the buses ply on the road?

Solution

## Let the speed of each bus = v km/hThe distance between the nearest buses plying on either car = vT km...(i)For buses going from town A to B:Relative speed of bus in the direction of motion of man = (v - 20)Buses plying in this direction go past the cyclist after every 18 min. Therefore, separation between the buses= (v - 20)$$\times$$(18/60)From (i), (v - 20)$$\times$$(18/60) = vT     ...(ii)For buses coming from B to A:The relative velocity of bus with respect to man = (v + 20) Buses coming from town B past'the cyclist after every 6 min,$$\therefore$$ (v + 20)$$\times$$(6/60) = vT     ...(iii)Solving (ii) and (iii), we get\v = 40 km/h and T = 2/30 hPhysics

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