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calculating upthrust? (really basic physics question) watch

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    What is the upthrust on a 1cm diameter steel ball in water?
    Density of steel = 8100kgm^-3
    Density of water = 1000kgm^-3

    if i were given the coefficient of viscosity id probably be able to work this out. any ideas?

    thanks in advance
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    Upthrust = Weight of Fluid Displaced
    Hence , mass of water displaced = density * volume = (1000) * (4/3 pi (1/100)^3)
    Hence weight displaced = mass * g = (1000) * (4/3 pi (1/100)^3) * 9.81 = Upthrust

    Coefficient of visc needed only for drag force....

    Upthrust + Drag = Weight of ball
    [at terminal velocity]
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    (Original post by antonfigo)
    Upthrust = Weight of Fluid Displaced
    Hence , mass of water displaced = density * volume = (1000) * (4/3 pi (1/100)^3)
    Hence weight displaced = mass * g = (1000) * (4/3 pi (1/100)^3) * 9.81 = Upthrust

    Coefficient of visc needed only for drag force....

    Upthrust + Drag = Weight of ball
    [at terminal velocity]
    hmm the answer should be 5.1 x 10^-3.

    is anything supposed to be done with the steel density value?
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    5.1x10^-3 or 4.1x10^-3
    Remember to convert 1 cm to 1/100 m

    No...Steel density value is not needed for upthrust...but we need steel ball's volume which is equal to volume of water displaced...
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    antonfigo has used 1cm in the calculation, but this is the diameter of the sphere. The formula requires the radius; half of this.
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    (Original post by Stonebridge)
    antonfigo has used 1cm in the calculation, but this is the diameter of the sphere. The formula requires the radius; half of this.
    Oh yea!
    I overlooked that :P ...now theres the real answer
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    1. Calculate the volume of the displaced liquid (volume of the block or object)
    2. Calculate the mass of the displaced liquid using the formula=density x volume
    3. Calculate the weight of the displaced liquid using the formula weight=massx10
    Always write it down in Newton or N in kilograms so if the answer is 1.0x20=20grams its 0.020 kg then you use the formula weight = massx10 so the answer is: 0.20N
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    (Original post by Ripiramon)
    1. Calculate the volume of the displaced liquid (volume of the block or object)
    2. Calculate the mass of the displaced liquid using the formula=density x volume
    3. Calculate the weight of the displaced liquid using the formula weight=massx10
    Always write it down in Newton or N in kilograms so if the answer is 1.0x20=20grams its 0.020 kg then you use the formula weight = massx10 so the answer is: 0.20N
    Welcome to TSR physics.

    Thanks for this.

    This thread was started in 2010 and is now closed.
 
 
 
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