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Physics Puzzle Problem

  1. Jan 21, 2015 #1
    So I've been trying to do some physics puzzles and I've come across this in a book called "200 puzzling physics problems." The solution in the back makes no sense to me and I can't seem to figure it out by myself. Can anyone help me?

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  2. jcsd
  3. Jan 22, 2015 #2

    Bystander

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  4. Jan 22, 2015 #3

    A.T.

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    What about it makes no sense?
     
  5. Jan 22, 2015 #4

    Bystander

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    I was answering the riddle, not denying assistance.
    Yes, I'll echo A.T., "what about it makes no sense?"
     
  6. Jan 22, 2015 #5

    phinds

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    Really? You reckon that would be true if the diameter of the bowl is 11cm ? This is a chain pulling it up, not a welded solid handle
     
  7. Jan 22, 2015 #6

    Bystander

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    I'll give you a hint since the OP hasn't been back to say what the bother is: "Two points."
    You meant "immersion depth?" rather than "diameter," in which case, there's insufficient information.
     
  8. Jan 22, 2015 #7

    phinds

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    I can only think that we must be interpreting the problem statement differently. I agree there is insufficient information for my interpretation, but that is still my reading of the problem. That is, I read it as a very clearly stated problem that provides insufficient information for an answer.
     
  9. Jan 22, 2015 #8

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    I'll give the OP the rest of the day, then "spill the beans" come evening.
     
  10. Jan 22, 2015 #9

    phinds

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    AAAARRRRGGGHHHH & dammit !! I obviously can't read. The diameter is given. Forget everything I've said in this thread. In fact, forget I'm even a member here! o:)

    Oh, and yes, I agree w/ you on this now (even though I'm not actually here)
     
  11. Jan 22, 2015 #10
    That solution on the back makes no sense linguistically. Here is my thinking: In the worst case scenario the bowl would be turning around the center of the circle it is a half of. Since the left most point on the bowl goes up by 10cm the right most point must go down 10cm, and this is exactly the boundary point for water spilling in. However, since the chain is applying an upward force on the bowl, the buoyant force would cause the entire bowl to move upwards. Thus the rotation of the bowl around its center only partially contributes to the leftmost point's moving upwards, and the rest is due to the buoyant force. Thus water will not flow in.
     
  12. Jan 22, 2015 #11

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    What solution? On the back of what?

    Your thinking is exactly what I came up with. The only way to reach water level on the low side is if the bowl has zero mass, and no such specification was made in the problem statement.
     
  13. Jan 23, 2015 #12

    jh0

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    I googled 200 puzzling physics problems pdf and the second link goes to a complete pdf of the book. I don't know if it is allowed to post a link due to copyright issues.

    Well, the correct solution is, as I expected, what c++guru said. You can find it in page 85 if you find the pdf. I do not see any problem with the solution, it makes sense.

    The bowl is made of copper, so it's denser than the water, and it contains fish soup, which is safe to assume that has approximately the same density as water. Therefore we can ascertain that the level of the soup must be below the lake’s level. Both the buoyant force and the soup’s weight are vertical forces that go through the sphere's geometrical centre. But the centre of mass of the bowl is below the hemisphere’s geometrical centre, so the system acts as a pendulum.

    In order to tilt the hemispherical bowl the chain has to exert an upwards force on the rim, this will lift the bowl, thus preventing the water to go over the bowl’s rim.
     
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