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# work watch

1. A cable of length 50 meters and density 4 kilograms per meter hangs over the edge of a skyscraper.
What work is needed to pull the whole cable to the top of the building?

TIP

When x meters of the cable are still hanging, think of the cable as an object of mass 4x. The force on the object is mass times acceleration due to gravity. So the force on the object is (4x)(9.8). Integrate.

Now i thought that the work= integral from a to b force[x]dx
force =(4x)(9.8)=39.2x
therefore work =integral from 0 to 50 (39.2)x dx=49000

Is this right??/
2. Can't this be done without using Calculus?

Its a 200kg object being lifted (an average) of 25m, against gravity (g = 9.8). (25m becuase the bottom bit is being lifted 50m and the top bit being lifted 0m)

So 200 * 9.8 * 25 = 49000 J

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Updated: December 23, 2005
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