# Ellipsoid: Oblate spheroid

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Joined: Feb 16 2013 - 11:32pm
Points: 2186
Ellipsoid: Oblate spheroid

A spheroid is formed by revolving an ellipse about its minor axis whose length is one-third that of the major axis. Find the length of the semi minor axis if the volume of the ellipsoid is 768 pi cubic feet.

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Joined: Feb 21 2013 - 11:07am
Points: 123
Re: Ellipsoid

2b = 1/3 (2a)
a = 3b

V = 4/3 pi a^2 b
768 = 4/3 pi (3b)^2 b
768 = 12pi b^3
b = 2.731 ft

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Joined: Feb 16 2013 - 11:32pm
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Re: Ellipsoid

according to the book, the answer must be 4 ft.

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Joined: Feb 21 2013 - 11:07am
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Re: Ellipsoid

If revolved about the major axis the answer is b = 3.94 cm. The formula for volume is V = 4/3 pi ab^2.

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Joined: Feb 16 2013 - 11:32pm
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Re: Ellipsoid

thanks

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