Multiple choice

Two trains 121 m and 99 m in length are running in opposite directions with velocities 40 $km \ h^{-1}$ and 32 $km \ h^{-1}$. In what time they will completely cross each other?

  1. 9 s

  2. 11 s

  3. 13 s

  4. 15 s
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Relative speed = 40 + 32 = 72 km/h = 72 * (5/18) = 20 m/s. Total distance = 121 + 99 = 220 m. Time = 220 / 20 = 11 s.

AI explanation

The total distance to be covered is the sum of the lengths of the two trains, giving 121 m plus 99 m equal to 220 m. Because they are moving in opposite directions, their relative speed is the sum of their speeds, which gives 40 km/h plus 32 km/h equal to 72 km/h. Converting this relative speed to meters per second gives 72 multiplied by (5 divided by 18), which equals 20 m/s. Using the time formula where time equals distance divided by speed, the time taken is 220 m divided by 20 m/s, which results in 11 s.

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