Work lifting cable and work pumping water

AI Thread Summary
When calculating the work done lifting a cable, the integral must be split because each segment of the cable is lifted different distances. In contrast, when pumping water out of a container, the limits of integration can be adjusted without needing to split the integral, as the water's center of mass is consistently at the height of the tank. For example, if a tank is 4 ft tall and you want to leave 1 ft of water, the limits can simply be changed from 0 to 3 ft. This approach simplifies the calculation of work done. Understanding these integral adjustments is crucial for accurately determining work in both scenarios.
demonelite123
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so i know that when there is a cable hanging from say a building that is taller than the length of the cable and you want to find the work done lifting half of the cable, you have to split the integral up since each "small piece" of rope in the first half gets lifted up a variable amount while each "small piece" of rope in the 2nd half gets lifted the same amount.

now when you are finding the work done by pumping water, let's say the problem is to find the work done in pumping water out of the top of the container so that only a depth of 1 ft of water remains. would you have to split up the integral in a similar way to the cable problem described above? or could you just adjust the limits of integration accordingly. for example if the tank is 4 ft tall and the limits to find the work to pump out all the water is from 0 to 4. could you change it so that the limits become from 0 to 3 to find the work needed to pump the water out so that 1ft depth remains?
 
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The center of mass of the water you are pumping out has to reach the height of the tank.
 
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