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Old 2014-09-29, 23:10   #1
MattcAnderson
 
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"Matthew Anderson"
Dec 2010
Oregon, USA

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Wink flagpole puzzle

Hi Math people,

I have a fun puzzle for you today.

Two flagpoles are each 100 feet high. A rope 150 feet long is strung between the tops of the flagpoles. At its lowest point the rope sags to within 25 feet of the ground. How far apart are the flagpoles?

Regards,
Matt
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Old 2014-09-29, 23:21   #2
Batalov
 
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Well, it would have been a hell of a problem (with knowing the chain curve's formula, which is cosh(), and knowing how to integrate the sqrt(1+f'2))... but there's only enough rope to be simply folded together twice 75 ft. The flagpoles are zero ft apart..
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Old 2014-09-30, 05:01   #3
MattcAnderson
 
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Batalov is right. Most people don't know about the mathematical curve that is the Catenary and equivalently hyperbolic cosine.
http://en.wikipedia.org/wiki/Catenary

Maybe some others would like to chime in on this one.

Regards,
Matt
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Old 2014-09-30, 17:18   #4
MattcAnderson
 
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Hi math people,

I have attached an answer page for the flagpole challenge.

Regards,
Matt
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File Type: pdf ropes answer page.pdf (278.2 KB, 250 views)
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Old 2014-09-30, 21:14   #5
ewmayer
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I was presented this same one on a paper napkin by a would-be stump-the-math-geek-er back in college - I believe it is designed to confuse those who *are* familiar with catenaries and such, by getting one to bog oneself down in the maths, thus missing the "trivial catenary" no-maths-other-than-division-by-2-required answer.

(And yes, I did quickly get the "null result" way back when.)

But, did we really need a "answer page" for this?
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