mersenneforum.org flagpole puzzle
 Register FAQ Search Today's Posts Mark Forums Read

2014-09-29, 23:10   #1
MattcAnderson

"Matthew Anderson"
Dec 2010
Oregon, USA

7×89 Posts
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
Attached Files
 ropes puzzle page.pdf (272.2 KB, 180 views)

 2014-09-29, 23:21 #2 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 916110 Posts 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..
 2014-09-30, 05:01 #3 MattcAnderson     "Matthew Anderson" Dec 2010 Oregon, USA 11578 Posts 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
2014-09-30, 17:18   #4
MattcAnderson

"Matthew Anderson"
Dec 2010
Oregon, USA

7×89 Posts

Hi math people,

I have attached an answer page for the flagpole challenge.

Regards,
Matt
Attached Files
 ropes answer page.pdf (278.2 KB, 250 views)

 2014-09-30, 21:14 #5 ewmayer ∂2ω=0     Sep 2002 República de California 266A16 Posts 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?

 Similar Threads Thread Thread Starter Forum Replies Last Post Harrywill Puzzles 4 2017-05-03 05:10 Uncwilly Puzzles 75 2012-06-12 13:42 henryzz Puzzles 4 2007-09-23 07:31 nibble4bits Puzzles 37 2006-02-27 09:35 Orgasmic Troll Puzzles 6 2005-12-08 07:19

All times are UTC. The time now is 05:30.

Sun Nov 29 05:30:32 UTC 2020 up 80 days, 2:41, 3 users, load averages: 0.69, 1.30, 1.53