$\"\"$

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Volume of the disk is $\"\"$ .

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Weight of the disk is $\"\"$ .

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Distance the disk of the water moved is $\"\"$ .

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Find the value of $\"\"$ in terms of $\"\"$ .

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$\"\"$ .

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Write the force increment as $\"\"$ .

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Note that distance $\"\"$ is moved from the bottom of the tank must be moved to $\"\"$ .

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Therefore the increment of the work is $\"\"$ .

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Substitute the value of $\"\"$ and $\"\"$ in the equation $\"\"$ .

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$\"\"$

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$\"\"$

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Because the tank is half full $\"\"$ ranges from $\"\"$ to $\"\"$ .

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Calculate the work required to empty the tank by Substituting the equation $\"\"$

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in equation $\"\"$ .

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$\"\"$

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Apply integration :

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$\"\"$

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$\"\"$

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The work required to empty the tank is $\"\"$ or $\"\"$ .