Halfing 3D Shapes

This entry is part 6 of 71 in the series Durtles Problems of the Weeks
Problem of the Week #6: Monday Feb. 13th, 2023
As before, these problems are the results of me following my curiosity, and I make no promises regarding the topics, difficulty, solvability of these problems.
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a). If we were to cut a cone, of base radius r and height h, parallel to its base so that the top portion and the bottom portion have the same volume, how far from the top (pointy end) should we cut?

b). If we were to cut a frustum of a cone (a cone with its top cut off parallel to its base), with bottom radius R, top radius r, and height h, parallel to its base so that the top and bottom portions have the same volume, how far from the top (smaller circle) should we cut?

c). If we were to cut a hemisphere, of radius r, parallel to its base so that the top and bottom portions have the same volume, how far from the top (spherical end) should we cut?

d). If we were to cut a frustum of a hemisphere (a hemisphere with its top cut off parallel to its base), with bottom radius R and top radius r, parallel to its base so that the top and bottom portions have the same volume, how far from the top (smaller circle) should we cut?

e). Share your own problem inspired by these considerations.

f). Show one of these questions to a friend/colleague/student/family member to start a mathematical discussion.

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