Tunnel length from crossing time A train 700 m long runs at 72 km/h and crosses a tunnel completely in 1 minute. What is the length of the tunnel?
Aptitude
Problems on Trains
Difficulty: Easy
Choose an option
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A700 m
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B600 m
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C550 m
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D500 m
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ENone of these
Answer
Correct Answer: 500 m
Explanation
Introduction / Context:Tunnel problems require adding the tunnel length to the train length for total distance covered during the crossing interval. Uniform motion assumptions apply.
Given Data / Assumptions:
- Train length = 700 m.
- Speed = 72 km/h = 20 m/s.
- Time t = 60 s.
Concept / Approach:Compute total distance in the given time, then subtract the train length to isolate the tunnel length.
Step-by-Step Solution:
D = v * t = 20 * 60 = 1200 mTunnel length = D - 700 = 500 mVerification / Alternative check:Recompose: 700 + 500 = 1200 m in 60 s at 20 m/s. This checks out.
Why Other Options Are Wrong:700 m, 600 m, 550 m: All give totals different from 1200 m in 60 s at 20 m/s.
Common Pitfalls:Using only tunnel length in D = v * t; you must include the whole train length during clearing.
Final Answer:500 m