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Journal of No. 118


February 12th, 2004

Mars and math @ 04:39 pm

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Latest Mars photo from the rover.

Math puzzle for the day.
You have a sphere. A cylindrical hole is drilled through the center of the sphere. The length of the hole from end to end is 6 cm. What is the volume of the pierced sphere?

It's wacky... you don't need to know the radius of the sphere or the radius of the hole. Confused? This answer is not likely to help much.
 
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From:the_undertow
Date:February 12th, 2004 08:08 pm (UTC)
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reading the lil answer hurt my head. i still dont really get it. but i made a nice drawing.
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From:essentialsaltes
Date:February 13th, 2004 03:11 pm (UTC)

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i still dont really get it. but i made a nice drawing.

I think that describes a good fraction of your physics homeworks.

The lazy physicist way to do the problem is to say, "well, if it doesn't matter what the radius of the sphere is, then I'll pick a sphere with diameter 6cm. Then the hole will be a hair thin little line through it, which won't take any volume away. So the 'leftover' volume is the same as a sphere of radius 3 = 36pi cc.

That guy does some wicked solid geometry that I don't remember, but I got the answer by doing some calculus: the 'washer' method of calculating volumes of solids of revolution.

Fortunately, I won't bore you with more detail, because you're still working on derivatives, and the washer method uses integrals.

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From:the_undertow
Date:February 13th, 2004 08:06 pm (UTC)

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ah i see. i think we did that in giese's class. ...damn now i want angelcake :d

Journal of No. 118