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Putnam
1942 Putnam
A5
A5
Part of
1942 Putnam
Problems
(1)
Putnam 1942 A5
Source: Putnam 1942
3/1/2022
A circle of radius
a
a
a
is revolved through
18
0
∘
180^{\circ}
18
0
∘
about a line in its plane, distant
b
b
b
from the center of the circle, where
b
>
a
b>a
b
>
a
. For what value of the ratio
b
a
\frac{b}{a}
a
b
does the center of gravity of the solid thus generated lie on the surface of the solid?
Putnam
ratio
Torus