GATE 2017 CE (CE2) – Question 65
An observer has eye level 5 m above sea level and sees the top of a 40 m high lighthouse. The maximum distance from the lighthouse, to one decimal place, is ______ km.
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Correct answer: 32.5 to 33.5
Explanation
Using the conventional combined curvature and refraction correction, horizon distance is approximately $3.86\sqrt h$ km for h in metres. Add the two horizons: $D=3.86(\sqrt5+\sqrt{40})=33.046$ km, or 33.0 km. The refraction convention is needed to match the official interval.