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Putnam 1942 A5

Source: Putnam 1942

March 1, 2022
PutnamratioTorus

Problem Statement

A circle of radius aa is revolved through 180∘180^{\circ} about a line in its plane, distant bb from the center of the circle, where b>ab>a. For what value of the ratio ba\frac{b}{a} does the center of gravity of the solid thus generated lie on the surface of the solid?
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