calculating upthrust? (really basic physics question) Watch

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dumb maths student
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#1
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#1
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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antonfigo
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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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dumb maths student
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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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antonfigo
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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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Stonebridge
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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.
antonfigo
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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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Ripiramon
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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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Stonebridge
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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.

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