Horizon

The top of a lighthouse is 19 m above the sea. How far away is an object just "on the horizon"? [Assume the Earth is a sphere of radius 6378.1 km.]

Correct answer:

x =  15.6 km

Step-by-step explanation:

R=6378.1 km h=19 m=0.019 km  (R+h)2=R2+x2 x2=(R+h)2R2 x2=R2+2Rh+h2R2 x2=2Rh+h2 x=2Rh+h2=15.6 km

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