Multiple choice

There are two trains going in the same direction. The speed of the faster train is twice as much as the slower train. They take 60 sec to cross each other while going in the same direction. How much time do they take to completely cross each other, if they run in opposite directions?

  1. 20 sec

  2. 30 sec

  3. 2 min

  4. 3 min
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A Correct answer
Explanation

Let speeds be v and 2v. Relative speed same direction = v. Relative speed opposite = 3v. Time = Distance / Relative Speed. 60 = D / v, so D = 60v. Time opposite = D / 3v = 60v / 3v = 20 seconds.

AI explanation

Let the slower train speed be v and the faster train speed be 2v, making the relative speed in the same direction equal to v. Let the sum of their lengths be D, so using the relative speed formula D divided by v equals 60, meaning D equals 60v. When travelling in opposite directions, their relative speed becomes the sum of their speeds, which is 3v. The time to cross is D divided by 3v, which substitutes to 60v divided by 3v, yielding 20 seconds. The result is 20 sec.

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