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Fluid mechanics problem

  1. Nov 19, 2012 #1

    utkarshakash

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    1. The problem statement, all variables and given/known data
    A piece of wood is floating in water kept in a bottle. The bottle is connected to an air pump. Neglect the compressibility of water. When more air is pushed into the bottle from the pump, the piece of wood will float with

    a)larger part in the water
    b)lesser part in the water
    c)same part in the water
    d)it will sink

    2. Relevant equations

    3. The attempt at a solution
    When more air is pushed the air pressure inside the bottle increases. But what will be its effect on floatation?
     
  2. jcsd
  3. Nov 19, 2012 #2

    haruspex

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    I'm not sure it's possible to answer this exactly without more knowledge of how wood responds to changes in air pressure. But I think they're trying to get you to consider what determines the volume of the block that's submerged. Can you state Archimedes' principle?
     
  4. Nov 20, 2012 #3

    utkarshakash

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    The liquid exerts a pressure on the solid immersed which is equal to the weight of the displaced fluid.
     
  5. Nov 20, 2012 #4

    haruspex

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    Shouldn't say pressure there. It exerts that force (upwards). Pressure is force per unit area.
    When an object is floating, at rest, what force would that be equal to?
     
  6. Nov 20, 2012 #5

    utkarshakash

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    Weight of the displaced fluid which is equal to (Density of liq.*vol of solid immersed*g)
     
  7. Nov 20, 2012 #6

    haruspex

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    True, but what I meant was, what other force is it equal to?
     
  8. Nov 21, 2012 #7

    utkarshakash

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    Its own weight.(Mass*g)
     
  9. Nov 21, 2012 #8

    haruspex

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    Right. Now, what will the increased air pressure do to the mass and volume of the wood?
     
  10. Nov 22, 2012 #9

    utkarshakash

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    Nothing:biggrin:
     
  11. Nov 22, 2012 #10

    haruspex

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    Well, it won't change the mass, but it might squeeze it a bit.
     
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