Multiple choice

Two trains of equal length, running with the speeds of 40kmph and 60 kmph, take 40 seconds to cross each other while they are running in the same direction. What time will they take to cross each other if they are running in opposite directions?

  1. 8 sec.

  2. 10 sec.

  3. 12 sec.

  4. 9 sec.

  5. 6 sec.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let L be the length of each train. Total distance = 2L. Relative speed in same direction = 60 - 40 = 20 km/h = 5.55 m/s. 2L = 5.55 * 40 = 222.22 m. Relative speed in opposite direction = 60 + 40 = 100 km/h = 27.77 m/s. Time = 2L / 27.77 = 222.22 / 27.77 = 8 seconds.

AI explanation

Using the formula time equals total distance divided by relative speed, let the length of each train be L. In the same direction, the relative speed is 60 minus 40, which is 20 kmph or 50/9 m/s. Since they take 40 seconds to cross, 2L equals 40 times 50/9, making 2L equal to 2000/9 meters. In the opposite direction, their relative speed is 60 plus 40, which is 100 kmph or 250/9 m/s. The time to cross is total distance divided by relative speed: (2000/9) divided by (250/9) equals 8 seconds.

Keep practicing — related questions