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HELP with Force

  1. Jan 21, 2005 #1
    HELP with Force!!

    I've got a "dilemma" here about Force:
    " Containers with different volumes but with the same areas at the bottom are filled with water of equal mass. Will the Force applied to the bottom of containers vary according to container?"

    First of all I guess Force must be equal to the Weight [W] of water which is same for all containers W=mg=F , but on the other hand if I calculate it from pressure F=PxA=dghA=dgV (P-pressure,A-area at the bottom, d-density of liquid , V-volume of container) and it varies due to the volume of container.
    :confused:
    Thanks..........
     
  2. jcsd
  3. Jan 21, 2005 #2

    dextercioby

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    The second part of the reasoning is wrong...Tell me why...

    Daniel.
     
  4. Jan 21, 2005 #3
    The weight of water must cause a pressure . Is that false?
     
  5. Jan 21, 2005 #4

    dextercioby

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    Of course not,it's the interpretation of "V" that is wrong...

    Daniel.
     
  6. Jan 21, 2005 #5
    The volume of container V=hxA Supposing it is sylindrical
     
  7. Jan 21, 2005 #6

    dextercioby

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    Prismatoid...But it's not the volume of the container... :wink: It's the volume of the fluid (i.e.water) which is the same for both containers,regardless of which is bigger...

    Daniel.

    P.S.Ergo,the force is "mg"...
     
  8. Jan 21, 2005 #7
    Thanks. But i still can't get how hxA=const if heigts are different? F=PxA=dxgxhxA
     
  9. Jan 21, 2005 #8

    dextercioby

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    The masses of water are the same.Ergo the volumes are the same.The containers have identical base area.Ergo the water has the same height in both containers.

    Daniel.
     
  10. Jan 21, 2005 #9
    But he containers have different shapes. One is wide another is narrow.
     
  11. Jan 21, 2005 #10

    dextercioby

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    WHAT???"but with the same areas at the bottom".Sounds familiar??Your very own hands wrote it in the first post...

    Daniel.
     
  12. Jan 21, 2005 #11
    Same area but not same shape. one gets wider from the bottom but another is narrow
     
  13. Jan 21, 2005 #12

    dextercioby

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    How do you know that???Was that specified in your problem???U said "sylinder" (sic),now u make it some weird shape...??

    Daniel;
     
  14. Jan 21, 2005 #13

    dextercioby

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    Can't u make a link,or something??Post it on
    www.imageshack.com And then insert the link in the message...

    Daniel.

    PS.you should have said that in the first place...
     
  15. Jan 21, 2005 #14

    Are you saying that the bottoms are not flat?
     
  16. Jan 21, 2005 #15

    dextercioby

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    I thought this problem was gonna be simple,but he insists it's more than what i thought previously... :confused:

    Anyway,let's hope he can come up with a drawing...

    Daniel.
     
  17. Jan 21, 2005 #16
    tried to attach
     

    Attached Files:

    • F.jpg
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  18. Jan 21, 2005 #17

    dextercioby

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    And the question is the same??Pressure force acting on the base??It's the hydrostatic pressure times the area of the base.The hydrostatic pressure is the product between the water density,the "g" acceleration and the height of the water column.

    In which case the height of the colum is greatest...??

    Daniel.
     
  19. Jan 21, 2005 #18
    The height is greatest in narrow one(D) but what about F=W=mg ? that's the point where i am confused.
     
  20. Jan 21, 2005 #19

    Doc Al

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  21. Jan 22, 2005 #20
    In that post you answered about pressure. I need help with force applied
     
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