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Question : Two train station are 50 km apart. One afternoon two trains start towards each other, one from each station. Just as the trains pull out of the station, a bird springs into the air in front of the first train and flies to the front of the second train. When it reaches the second train, it turns back and flies towards the first train. The bird continues to do this until the trains meet. If both trains travel at the rate of 25 km/h, and the bird flies at 100 km/h, how many kilometres will the bird have flown before the trains meet?

Doubt by Yashika 

Solution : 
Distance between the two trains = 50 km
Trains are approaching with a relative speed of = [25-(-25)] = 50 km/h

Time taken by the trains to meet
= Distance/speed
= 50 /50
= 1 hr

Speed of the bird = 100 km/h
Distance covered by the bird
= Speed of Bird × Time Taken by the trains to meet
= 100×1
= 100 km

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Similar Question :

Two trains A and B are headed towards each other on the same straight track, each having speed of 20 km/h. A bird that can fly at 40 km/h, flies off train A, when they are 40 km apart and heads directly for the train B. On reaching B, the bird flies back to A and so on.

a) Find the number of trips, the bird can make before the two trains meet each other. 

b) What is the total distance travelled by the bird. 

Ans : a) Infinite b) 40 m