A 220 m long train passes a signal post in 12 seconds. What is the speed of the train in km/h?
Aptitude
Problems on Trains
Difficulty: Easy
Choose an option
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A72 km/h
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B60 km/h
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C66 km/h
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D69 km/h
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E54 km/h
Answer
Correct Answer: 66 km/h
Explanation
Introduction / Context:Passing a post uses only train length. Speed equals length divided by time (in m/s), converted to km/h by multiplying by 3.6.
Given Data / Assumptions:
- L = 220 m.
- t = 12 s.
Concept / Approach:v_mps = 220/12 = 55/3 ≈ 18.3333 m/s. Convert to km/h: v_kmph = v_mps * 3.6.
Step-by-Step Solution:
v_mps = 220/12 = 18.3333…v_kmph = 18.3333 * 3.6 = 66 km/h.Verification / Alternative check:Reverse check: 66 km/h = 18.3333 m/s; in 12 s distance = ~220 m—consistent.
Why Other Options Are Wrong:54, 60, 69, 72 km/h are off the exact conversion.
Common Pitfalls:Using 18/5 instead of 5/18 or vice versa incorrectly; rounding too early.
Final Answer:66 km/h