Question:medium

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

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When crossing a tunnel, add the train length to the tunnel length to get total distance covered.
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: Work in kilometres and hours instead of converting the speed.
The train's speed is 90 km/hr, and one minute is \( \frac{1}{60} \) of an hour.

Step 2: Find the total distance covered in that time.
Distance \( = \text{speed} \times \text{time} = 90 \times \frac{1}{60} = 1.5 \) km, which is \( 1.5 \times 1000 = 1500 \) metres.

Step 3: Subtract the length of the train.
This total distance of 1500 metres covers both the train's own length and the tunnel, so the tunnel length is \( 1500 - 600 = 900 \) metres.

Step 4: State the final length.
The tunnel is 900 metres long.
\[ \boxed{900 \, \text{m}} \]
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Approach Solution -2

Instead of converting the speed into metres per second, it can be simpler to convert it directly into metres per minute, since the crossing time given is already in minutes, and then check each tunnel option against that.

  1. 500 meters: The train's speed of 90 km/hr equals \( \frac{90 \times 1000}{60} = 1500 \) metres per minute, so in the one minute it takes to cross, the train covers 1500 m in total. Adding 500 m to the train's own 600 m gives only 1100 m, short of the 1500 m actually covered.
  2. 550 meters: Adding 550 m to 600 m gives 1150 m, still well below the 1500 m travelled in that one minute.
  3. 600 meters: Adding 600 m to 600 m gives 1200 m, again less than 1500 m.
  4. 900 meters: Adding 900 m to 600 m gives exactly 1500 m, matching the total distance covered in one minute at this speed.

Converting the speed directly into metres per minute and matching the total distance to the sum of train length and tunnel length confirms the tunnel is 900 metres long.

So the correct answer is 900 meters.

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