Problem on Trains
- A and B are two stations, a train goes from A to B at 64 km/hr. and return to A at a slower speed. If its average speed for the whole journey is 56 km/hr. at what speed did it return ?
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Let the required speed be y km/hr.
Then, ( 2 x 64 ) x [ y / (64 + y)] = 56Correct Option: B
Let the required speed be y km/hr.
Then, ( 2 x 64 ) x [ y / (64 + y)] = 56
⇒ 128y = 64 x 56 + 56y
∴ y= (64 x 56 ) / 72
= 49.77 km/hr.
- A train 270 metres long is moving at a speed of 25 kmph. It will cross a man coming from the opposite direction at a speed of 2 km per hour in ?
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Relative speed = (25 + 2) = 27 km/hr = 27 x (5/18) m/sec. = 15/2 m/sec.
Correct Option: A
Relative speed = (25 + 2) = 27 km/hr = 27 x (5/18) m/sec. = 15/2 m/sec.
Time taken by the train to pass the men. = 270 / (15/2) = 36 sec.
- A train 300 meters long passes a standing man is 15 seconds. The speed of the train is ?
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∴ Speed = Distance / Time = (300/15)
Correct Option: D
∴ Speed = Distance / Time = (300/15)
= 20 m/sec
= (20 x 18) / 5 = 72 km/hr
- The length of the train that takes 8 second to pass a pole where it runs at a speed of 36 km/hr is ?
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Speed of the train = (36 x 5)/18 = 10 m/sec.
Distance = (Time x Speed ) = (8 x 10 ) = 80 metersCorrect Option: D
Speed of the train = (36 x 5)/18 = 10 m/sec.
Distance = (Time x Speed ) = (8 x 10 ) = 80 meters
∴ Length of the train = 80 meters
- A train 280 meters long is moving at a speed of 60 km/hr. The time taken by the train to cross a platform 220 meters long is ?
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∵ Speed of the train = 60 x (5/18) m/sec = 50/3 m/sec
∴ Time taken by the train to cross the platform
= Time taken by it to cover (280 + 220) mCorrect Option: C
∵ Speed of the train = 60 x (5/18) m/sec = 50/3 m/sec
∴ Time taken by the train to cross the platform
= Time taken by it to cover (280 + 220) m
= (500 x 3/50) sec = 30 sec
