Multiple choice

A train passes an electric post in 10 second and a bridge of length 2 km in 110 seconds. The speed of the engine is:

  1. 18 kmph

  2. 36 kmph

  3. 72 kmph

  4. 90 kmph
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let L be the length of the train and v be the speed. L = v * 10. (L + 2000) = v * 110. Substituting L: 10v + 2000 = 110v. 100v = 2000, so v = 20 m/s. 20 m/s * 18/5 = 72 kmph.

AI explanation

Let the length of the train be L meters; crossing a post takes 10 seconds, meaning the train's speed is L/10 m/s. The 2 km bridge is 2000 m long, so crossing it takes 110 seconds, meaning the train covers L + 2000 meters in 110 seconds at the same speed. Equating the speeds gives (L + 2000) / 110 = L / 10, and solving this yields L = 200 m. The speed is therefore 200 divided by 10, which is 20 m/s, and converting this to km/hr by multiplying by 18/5 gives 72 kmph.

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