Multiple choice

Two trains each of length $100\ m$ moving parallel towards each other at speed $72\ km/h$ and $36\ km/h$ respectively. In how much time will they cross each other?

  1. $4.5\ S$
  2. $6.67\ s$
  3. $3.5\ s$
  4. $7.25\ s$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Relative speed = 72 + 36 = 108 km/h = 108 * (5/18) = 30 m/s. Total distance to cover = 100 + 100 = 200 m. Time = Distance / Speed = 200 / 30 = 6.67 s.

AI explanation

Since the trains move in opposite directions, their relative speed is the sum of their speeds: 72 km/h plus 36 km/h equals 108 km/h. Converting to m/s by multiplying by 5/18 gives a relative speed of 30 m/s. The total distance to cover is the sum of their lengths, 100 m plus 100 m, which equals 200 m; dividing 200 m by 30 m/s gives 6.67 s.

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