Question 1189863
A spherical buoy of radius 2 meters floats in a calm lake. 40 cm of the buoy are submerged. Place a coordinate system with the origin at the center of the sphere. Find an equation of the circle formed at the waterline of the buoy.
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The radius of the buoy is 200 cms
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Assuming "40 cms are submerged" means the center of buoy is 200 - 40 = 160 cm above the surface of the water:
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A right triangle can be formed.  The hypotenuse is 200 cm, one leg is 160 cm, and the 3rd side is the radius of the circle.
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{{{r = sqrt(200^2 - 160^2) = 120}}}
With the Origin at the center of the circle the equation is
{{{x^2 + y^2 = 120^2}}}