



 
Hi Jean, Wikipedia Has a concise statement of Archimedes' principle
The volume of a cone is given by
Thus from my diagram the weight of the buoy is \[W_B = \frac13 \pi \times R^2 \times H \times\mbox{ (the density of the buoy material.)} \] The buoyant force is equal to the weight of the fluid displaced by the buoy and this weight is given by \[W_F = \frac13 \pi \times r^2 \times h \times\mbox{ (the density of water.)} \] Thus, at any instance the force required by the crane is $W_B  W_F.$ Does this help? Write back if you need more assistance. Penny  


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