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Math Help - An oldie

  1. #1
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    An oldie

    Here's an oldie you might enjoy . . . or not.


    Two 20-foot poles are erected perpendicular to the ground.

    The ends of a 30-foot rope is attached to the tops of the poles.

    The rope hangs naturally and its lowest point is 5 feet from the ground.

    How far apart are the poles?
    Code:
          *               *
          |               |
          | *           * |
          |   *       *   |
       20 |       *       | 20
          |       :       |
          |       :5      |
          |       :       |
        --*-------+-------*--
          : - - - ? - - - :

    NOTE: Ropes, cables, etc. do NOT hang in a parabolic shape.
    . . . . . The shape is a catenary.


    If you already know the answer, please don't give it away.
    .
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by Soroban View Post
    Here's an oldie you might enjoy . . . or not.


    Two 20-foot poles are erected perpendicular to the ground.

    The ends of a 30-foot rope is attached to the tops of the poles.

    The rope hangs naturally and its lowest point is 5 feet from the ground.

    How far apart are the poles?
    Code:
          *               *
          |               |
          | *           * |
          |   *       *   |
       20 |       *       | 20
          |       :       |
          |       :5      |
          |       :       |
        --*-------+-------*--
          : - - - ? - - - :
    NOTE: Ropes, cables, etc. do NOT hang in a parabolic shape.
    . . . . . The shape is a catenary.

    If you already know the answer, please don't give it away.
    .
    Well I didn't know the answer but it took only ~5 seconds to deduce it.

    RonL
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  3. #3
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    Got it in two seconds before I've even finished reading the ques However, I wonder if the diameter of the poles should be taken into consideration :P
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  4. #4
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    I think, in white -> 0
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  5. #5
    MHF Contributor arbolis's Avatar
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    I didn't get it after about 4 minutes and I gave up! I leave a comment in white : I was thinking on the sketch... that is probably why I didn't get it. I could have sketch it on a sheet though. Nice one!
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  6. #6
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    Re :

    So what is the correct answer ?
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  7. #7
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by mathaddict View Post
    So what is the correct answer ?
    i believe Obsidantion has the right answer (post #4)
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  8. #8
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    Re :

    gotk it , the diagram brings confucion . haha , nice oldie
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  9. #9
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by mathaddict View Post
    gotk it , the diagram brings confucion . haha , nice oldie
    i agree. haha, i've tricked a lot of students with this since i saw it, because they all try to use the diagram to figure stuff out. and that whole explanation about catenaries (which i extended, of course) doesn't make things any easier.
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  10. #10
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    Quote Originally Posted by Soroban View Post
    Here's an oldie you might enjoy . . . or not.


    Two 20-foot poles are erected perpendicular to the ground.

    The ends of a 30-foot rope is attached to the tops of the poles.

    The rope hangs naturally and its lowest point is 5 feet from the ground.

    How far apart are the poles?
    Code:
          *               *
          |               |
          | *           * |
          |   *       *   |
       20 |       *       | 20
          |       :       |
          |       :5      |
          |       :       |
        --*-------+-------*--
          : - - - ? - - - :

    NOTE: Ropes, cables, etc. do NOT hang in a parabolic shape.
    . . . . . The shape is a catenary.


    If you already know the answer, please don't give it away.
    .
    Yeah, I got it, it's a Quadrilateral is formed with the height from string.., I won't tell you what type, that's a clue
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  11. #11
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    Quote Originally Posted by ice_syncer View Post
    it's a Quadrilateral
    What? No it's not.
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