Locate the COM of a uniform hemisherical solid with respect to 0 as shown in figure. (Radius = r)
Figure shows a hemisphere of mass M and radius R. To find its centre of mass (only y−coordiante), we consider an elemental disc of width dx, mass dm at a distance x from the centre of the hemisphere.This radius of this elemental disc will be given as r=√R2−x2
The mass dm of this disc can be given asdm=3M2πR3×πr2dx=3M2R3(R2−x2)dxycm of the hemisphere is given asycm=1M∫R0dm x=1M∫R03M2πR3(R2−x2)dx x=32πR3∫R0(R2−x2)x dxycm=3R8