Question:medium

A train 600 meters long is running at a speed of 90 kms/hr. If it crosses a tunnel in one minute, then the length of the tunnel is:

Updated On: Jul 15, 2026
  • 500 meters
  • 550 meters
  • 600 meters
  • 900 meters
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The Correct Option is D

Approach Solution - 1

Step 1: Convert the speed to metres per second.
Speed \( = 90 \) km/hr \( = 90 \times \frac{5}{18} = 25 \) m/s.

Step 2: Find the total distance covered in one minute.
Time \( = 1 \) minute \( = 60 \) seconds. Distance \( = \text{speed} \times \text{time} = 25 \times 60 = 1500 \) m.

Step 3: Subtract the train's own length.
When a train crosses a tunnel, the distance covered equals the tunnel length plus the train length. Tunnel length \( = 1500 - 600 = 900 \) m.

Step 4: Final Answer.
The train needs to cover its own length plus the tunnel's length to fully cross it, giving a tunnel length of 900 metres. \[ \boxed{900 \text{ m}} \]
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Approach Solution -2

When a train crosses a tunnel completely, the total distance it covers equals its own length plus the tunnel's length, so this can be set up as a direct equation with the tunnel length as the unknown, rather than computing the total distance and subtracting afterward.

  1. 500 meters: Let the tunnel length be \( L \). The equation is \( 600+L = \text{speed} \times \text{time} \). Substituting \( L=500 \) gives a left side of 1100 m, but the right side, using speed \( 25 \) m/s over 60 seconds, equals 1500 m, so the equation does not balance.
  2. 550 meters: Substituting \( L=550 \) gives a left side of 1150 m, still short of the 1500 m the right side produces, so the equation again fails to balance.
  3. 600 meters: Substituting \( L=600 \) gives a left side of 1200 m, which is still less than the 1500 m required, so this does not satisfy the equation either.
  4. 900 meters: Substituting \( L=900 \) gives a left side of \( 600+900=1500 \) m, which exactly equals the right side, \( 25 \times 60 = 1500 \) m, balancing the equation perfectly.

Setting up the crossing condition as an equation and substituting each candidate length shows only 900 m makes both sides equal.

Therefore, the correct answer is 900 meters.

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