Multiple choice

A train crosses a platform 100 m long in 15 seconds and a man standing on the platform in 10 seconds. What is the speed of the train?

  1. 62 km/hr

  2. 68 km/hr

  3. 72 km/hr

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Speed = Length / Time. Train passes man in 10s: Speed = L/10. Train passes platform in 15s: Speed = (L+100)/15. L/10 = (L+100)/15 => 15L = 10L + 1000 => 5L = 1000 => L = 200m. Speed = 200/10 = 20 m/s. 20 m/s * 3.6 = 72 km/hr.

AI explanation

Let the length of the train be L metres; its speed in metres per second is L divided by 10 because it crosses a man in 10 seconds. When crossing a 100 m platform, the train covers L + 100 metres in 15 seconds, making its speed (L + 100) divided by 15. Equating the two speed expressions gives L / 10 = (L + 100) / 15, which simplifies to 15L = 10L + 1000, meaning L = 200 m. The speed is 200 / 10 = 20 m/s, which converts to 20 multiplied by 18/5, yielding 72 km/hr.

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