Multiple choice

A train $700 m$ long is running at $72$ kmph . If it crosses a tunnel in $1$ minute, the length of the tunnel is :

  1. $700 m$
  2. $600 m$
  3. $550 m$
  4. $500 m$
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D Correct answer
Explanation

Speed = 72 kmph = 72 * 5/18 = 20 m/s. Time = 1 minute = 60 seconds. Distance = Speed * Time = 20 * 60 = 1200 m. Distance = Train length + Tunnel length. 1200 = 700 + Tunnel length. Tunnel length = 500 m.

AI explanation

First, convert the speed from kmph to m/sec by multiplying 72 by 5/18, which gives 20 m/sec. The total distance covered in 1 minute, or 60 seconds, is speed multiplied by time, so 20 multiplied by 60 equals 1400 meters. Since total distance equals the train length plus the tunnel length, the tunnel length is 1400 minus 700, which equals 500 meters.

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