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Pressure and resultant force

  1. Apr 28, 2008 #1
    1. The problem statement, all variables and given/known data

    ( athmosphere pressure is normal 101 kPa)
    A ”tub” has a form as a prism ( like on the pic ) with the following lengths
    Length: 2m
    Width : 0,75m
    height: 0,5m
    Whats the absolute pressure agains the sides at the bottom of the “tub” + resultant force

    [​IMG]


    2. Relevant equations

    I Think
    p=po + pgh


    3. The attempt at a solution


    (Im not sure about po and p )

    For the absolute pressure I got :
    P=Pa +pgh = 101 + 0,75*9,81*0,5 = 104,67 pa

    And the resultant force
    P = pgh = Resultantkraft: pgh = 0,75*9,81*0,5 = 3,675 pa
    I have done someting wrong havent i ?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 28, 2008 #2
     
  4. Apr 29, 2008 #3

    tiny-tim

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    Hi Newton86! :smile:

    erm … what's the tub filled with? :confused:

    and I don't think the width affects the pressure, does it? :smile:
     
  5. Apr 29, 2008 #4
    Hi again Tim:smile::smile:
    Its filled with water. And yeah you got a point with the width :tongue:

    I think I have it now after I see what pa and P is.

    absolute pressure:
    Pa +pgh = 101000 + 1000kg/m^3*9,81*0,5 = 105900 pa

    101kpa is 101000 pa and 1000kg/m^3 is the density of water.

    Resultant force:

    Resultantkraft: pgh = 1000kg/m^3*9,81*0,5 = 4900 pa

    does this make sense ?
     
  6. Apr 29, 2008 #5

    tiny-tim

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    Hi Newton86! :smile:

    Looks very good! :smile:

    (But I don't understand what they mean by "resultant force" … 49000pa is a pressure … pressure = force/area … do they mean resultant-force/area? :confused:)​
     
  7. Apr 29, 2008 #6

    tiny-tim

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    Hi Newton86! :smile:

    Looks very good! :smile:

    (But I don't understand what they mean by "resultant force" … 49000pa is a pressure … pressure = force/area … do they mean resultant-force/area? :confused:)​
     
  8. Apr 29, 2008 #7
    Dont ask me You are the smart one:wink:
    But the resultant force to the bottom of the "tub"
    I dont know but we got the information about lenght and width and so far i havent used that info, maybe i should :confused:
     
  9. Apr 29, 2008 #8

    tiny-tim

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    Hi Newton86! :smile:

    (hmm … sometimes they put in extra information just to test if you know what's relevant)

    Is the question asking for the "resultant force at the bottom of the tub", or for the total resultant force on all the sides of the tub, right up to the top?
     
  10. Apr 29, 2008 #9
    "The resultant force agains the bottom of the tub" I would say it also have info about a hatch but I think that is only relevant to the next question who is what the resultant force is agains the hatch..
     
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