Multiple choice

Two trains running at speeds of 36 kmph and 54 kmph, respectively cross each other in 10 sec, if they run in opposite directions. When they run in the same direction, a person sitting in the faster train observes that he crossed the other train in 20 seconds. Find the lengths of the two trains.

  1. 200 m, 50 m

  2. 100 m, 150 m

  3. 180 m, 70 m

  4. 125 m, 125 m
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B Correct answer
AI explanation

Convert the speeds to meters per second to get 10 m/s for the first train and 15 m/s for the second train. When moving in opposite directions, their relative speed is 25 m/s, so the sum of their lengths equals 25 m/s multiplied by 10 seconds, which is 250 m. When moving in the same direction, the relative speed observed by the person in the faster train is 5 m/s, meaning the length of the slower train is 5 m/s multiplied by 20 seconds, which equals 100 m. Subtracting this from the total length of 250 m gives the length of the faster train as 150 m, so the lengths are 100 m and 150 m.

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