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Mad About Physics book

  1. Jun 22, 2009 #1
    Does anyone own the Jargodzki and Potter book Mad About Physics? If so, could you examine braintwister no. 90, the three hole can? They seem to claim that, if you have a cylindrical can filled with water and there are three identical holes, one near the top, one near the middle, and one near the bottom, that the water will shoot the farthest horizontally from the middle one.

    What is the "trick" here? Have I missed a clever wording?
     
  2. jcsd
  3. Jun 22, 2009 #2

    Doc Al

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    No trick. Did you read the solution in the back of the book? The calculation is straightforward.
     
  4. Jun 23, 2009 #3
    I'm sorry. Poorly worded question. Why would someone be puzzled by this? It seems consistent with ordinary experience (except for the problem of crossing streams - that seems like more of a braintwister).
     
  5. Jun 23, 2009 #4

    Doc Al

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    I guess if you've never had the experience, it might not be obvious that the illustration is incorrect and that it's the middle stream that goes the farthest. When I first came across this problem (a gazillion years ago) I had to do the calculation to fully understand it.

    Maybe you're just too smart! :smile:
     
  6. Jun 23, 2009 #5
    I suspect I'm too literal. I often don't get satire (On the good side, that makes it hard to insult me) or jokes.

    Thanks. I just needed a second set of eyes to point out the puzzle.
     
  7. Jun 23, 2009 #6

    A.T.

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    I don't have the book. Is this an optimization problem of initial horizontal velocity vs. initial height? Is the can placed on the ground? If you hold it up it, could it change the result?
     
  8. Jun 23, 2009 #7
    Sure. That would make an interesting variation, that is, putting legs on the can.
     
  9. Jun 23, 2009 #8

    Danger

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    Well then, I guess that I won't be conversing with you much. :wink:
     
  10. Jun 23, 2009 #9

    RonL

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    Some may have noticed that about me as well.:biggrin:
     
  11. Jun 23, 2009 #10
    Actually, your post jogged my memory and I realized why I knew which hole would spurt the farthest. When I was a kid, we used to shoot holes in 55 gallon rain barrels. Thank god the steam trains went away just about the time I got my first gun or I'd probably have tried the water tanks for those.:biggrin:

    Glad to see you're staying one step ahead of the Mounties.
     
  12. Jun 24, 2009 #11

    Danger

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    Too cool. :rofl:
    Despite your denial, you obviously have a great sense of humour.
     
  13. Jun 24, 2009 #12

    Born2bwire

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    There is no better way to demonstrate the joys and laws of physics to youth than the after effects of high pressure gas expansions via exothermic chemical reactions.
     
  14. Jun 24, 2009 #13

    Danger

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    Hence my diet of beans and beer.
     
  15. Jun 24, 2009 #14
    So, do you wonder why just the sight of a post from you reminded me of doing something I absolutely should not have been doing?:blushing:
     
  16. Jun 24, 2009 #15

    Danger

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    Naw... I'm getting used to it.
     
  17. Jun 24, 2009 #16
    I took physics back in the dark ages before safety regs and political correctness. My General Physics professor had several demos in which he used a rifle. Gone are those days...
     
  18. Jun 25, 2009 #17
    I remember getting a physics question in an assignment that was kind of like this, but we had to use calculus to find the maximum range. You end up finding that the velocity is as if the water had fallen that distance due to gravity, then you also find that the middle is the best hight because of range being the maximum.
     
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