Multiple choice

Two trains $121$ and $99\ m$ in length respectively are running in opposite directions, one at the rate of $40\ km$ and the other at the rate of $32\ km$ an hour. In what time will they be completely clear of each other from the moment they meet?

  1. $110\ seconds$
  2. $99\ seconds$
  3. $88\ seconds$
  4. $11\ seconds$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The relative speed of the trains is 40 + 32 = 72 km/hr. Converting to m/s: 72 * (5/18) = 20 m/s. The total distance to cover is 121 + 99 = 220 m. Time = distance / speed = 220 / 20 = 11 seconds.

AI explanation

When two trains move in opposite directions, their relative speed is the sum of their speeds, so 40 km/hr plus 32 km/hr equals 72 km/hr. Converting this to m/s gives 72 multiplied by 5/18, which is 20 m/s. The total distance to clear each other is 121 m plus 99 m, totaling 220 m. The time is distance divided by speed, so 220 divided by 20 results in 11 seconds.

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