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\noindent {\bf Problem statement} A homogeneous liquid whose density
is 300 kg/${\rm m}^3$ fills three buried containers. The containers,
drawn below, are each 10 meters tall. The top of each container is at
ground level. All three containers have the {\it same} volume. The
middle container is a cylinder, and the other two are circular
cones. Which container needs the {\it least} amount of work to empty
(that is, to pump the liquid to ground level)?  Which container needs
the {\it most} work to empty? Justify your assertions by computing the
work necessary in each case. You may also discuss {\it why}\/ your
answer is correct!

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