Duplicate tunnel setup – compute tunnel length A 700 m train runs at 72 km/h and crosses a tunnel in 1 minute. What is the tunnel length?
Aptitude
Problems on Trains
Difficulty: Easy
Choose an option
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A500 m
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B550 m
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C600 m
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D700 m
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ENone of these
Answer
Correct Answer: 500 m
Explanation
Introduction / Context:This is the same structure as a prior item: total distance in the interval equals train length plus tunnel length. Convert speed and multiply by time to get distance.
Given Data / Assumptions:
- Train length = 700 m.
- Speed = 72 km/h = 20 m/s.
- Time = 60 s.
Concept / Approach:Compute D and subtract train length to find tunnel length.
Step-by-Step Solution:
D = 20 * 60 = 1200 mTunnel length = 1200 - 700 = 500 mVerification / Alternative check:Adding back: 700 + 500 = 1200 m in 60 s at 20 m/s — consistent.
Why Other Options Are Wrong:550 m and 600 m lead to too much distance; 700 m confuses tunnel length with total. Only 500 m works.
Common Pitfalls:Using only tunnel length in D = v*t. Always include the train length for clearing a tunnel.
Final Answer:500 m