Multiple choice

What is the ratio between times taken by a train $240$ m long to cross an electric pole and a bridge of $80$ m length?

  1. $2 : 3$
  2. $3 : 4$
  3. $4 : 5$
  4. $5 : 6$
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B Correct answer
Explanation

Time to cross pole = Length of train / Speed = 240 / v. Time to cross bridge = (Length of train + Length of bridge) / Speed = (240 + 80) / v = 320 / v. Ratio = 240 / 320 = 24 / 32 = 3 / 4.

AI explanation

The time to cross a stationary pole is determined by the formula time = length / speed, so the time taken is $240 / s$. To cross an 80 m bridge, the train must cover its own length plus the bridge length, making the total distance $240 + 80 = 320$ m, which takes $320 / s$. The ratio of these times is $(240 / s) : (320 / s)$, which simplifies to $240 : 320$ or $3 : 4$. The result is 3 : 4.

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