Multiple choice

A train running at the speed of 36 kmph takes 30 seconds to pass a bridge. It takes 14 seconds to pass a man running at 9 kmph in opposite direction. What is the length of the bridge?

  1. 200 metres

  2. 225 metres

  3. 100 metres

  4. 125 metres

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Train speed is 36 kmph = 10 m/s. Man speed is 9 kmph = 2.5 m/s. Relative speed when passing man = 10 + 2.5 = 12.5 m/s. Length of train = 12.5 * 14 = 175 meters. Time to pass bridge = 30s. Total distance = 10 * 30 = 300 meters. Bridge length = 300 - 175 = 125 meters.

AI explanation

The train speed of 36 kmph converts to 10 m/s, and the relative speed against the man running at 9 kmph is 36 plus 9, which equals 45 kmph or 12.5 m/s. Using the relative speed formula, the length of the train is 12.5 m/s multiplied by 14 seconds, resulting in 175 m. When passing the bridge at 10 m/s in 30 seconds, the total distance covered is 10 times 30, which equals 300 m. Subtracting the train length from this total distance gives a bridge length of 300 m minus 175 m, equaling 125 m. The length of the bridge is 125 metres.

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