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Another question,(hope it isnt boring)

  1. Jun 25, 2004 #1
    You are canoeing upstream of a river,the current against you is 3 mph.You are rowing at 4 and 1/4.Your hat falls onto the water and only after 45 minutes,you then realise that it is gone.in a split second you make an instantaneous,acceleration-free turnabout to get your hat.

    How long will it take for you to get it back?

    (this looks like a math question,but trust me it isnt.)
  2. jcsd
  3. Jun 25, 2004 #2


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    It's a viewpoint question. Did you read the fine book Count Down (about the Math Counts program)?
  4. Jun 25, 2004 #3
    i havent read any,but i have read richard feynmans "genius" book,an autobiography of his life.

    By the way,have you found the answer?:smile:
  5. Jun 26, 2004 #4
    No one would wear a valuable hat whilst canoeing, so it wouldn't matter if you didn't get the hat back. Therefore, no time, because I wouldn't get the hat. The. End.
  6. Jun 26, 2004 #5


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    you'd never get your hat because you'd always be travelling at the same speed after it with the current and be 45 mins behind, as no mention of any paddling was made in an attempt to retrieve the hat. Best guess anyway. that or an instantaneous acceleration free turnabout is impossible.
  7. Jun 26, 2004 #6
    Kurdt you almost got it correct(darn).when instantaneous free-acceleration turnabout is possible,the river and gravity becomes irrevelent.Focusing your point of view onto the hat..and you will see it keeping still.Realising it is missing,it will take you 45 mins to row back to where you lost it About the paddling thing,if it is acceleration-free,your own inertia will need no paddling,thats the part you sort of got correct. :smile:
    Last edited: Jun 26, 2004
  8. Jun 26, 2004 #7


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    The hat is at rest wrt the river flow (inertial frame!). So wrt the hat all the speeds go away and it's just a time problem.
  9. Jun 27, 2004 #8
    I agree.Just buy another hat. :tongue2:
  10. Jun 27, 2004 #9
    How much is that ?Is that cheap ?
    If that is, I suggest you buy 1000 hats and use one by one till the day you go to he||.
  11. Jun 27, 2004 #10
    i dunno about you guys, but im going to post a few more questions.By the way to find the answer you NEED the hat for the question.It dont matter whether its logical,or not.It is focused rather on inertial frame and point reference.
  12. Jun 27, 2004 #11


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    The hat will be 4950 ft from you when you make the turnabout. How long it takes you to get to it depends on the speed you move wrt to the hat's inertial frame. If you simply turn around but don't paddle after it, you will not move at all wrt that frame. If you continue rowing at 4 1/4, you'll get there in 13.2 minutes (to three significant figures).
  13. Jun 28, 2004 #12
    lol loseyourname, once you start calculating,you're already WRONG. the speeds, current,gravity are all irrelevent when it is acceleration-free.Without gravity, the hat will be in mid-air and stuck there,and gravity doesnt affect your current rowing and you continue rowing with no resistance whatsoever.The final answer will still be 45 mins.4950ft may be part of the process but in acceleration-free environment,(like self-adjoint said)it becomes only a time problem.By the way,the question itself in actual testing is given only 45 seconds to answer.
  14. Jun 28, 2004 #13
    The hat fell into the boat which had water in it. Pick it up and place it on you head.


    Turn the boat around drop anchor and wait until the hat comes to you, who said you were going against the current? The current against you is 3mph either way.

    The third is the normal obvious assumption.

    Books are what you need while you don't open the one you are born with. Real wisdom, mine, it comes from the water.
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