how can we find centre of mass of a solid cone????

For a solid cone, 

Let (Xc,Yc) are the coordinates of center of mass.

Then,

For symmetry consider the center of mass at Xc=0. Divide the cone in horizontal disks of mass then, dm=ρdV where, ρ is the density of material. (constant) In this case,

where r is the radius of the cone at an arbitrary height dy. Radius of cone depends upon the height of the cone. 

So, y=0 ; r=R (R is the base radius of the cone)

 y=h ; r=0.

Using point-slope form: 

Now, the volume

So,

So, the center of mass of solid cone is at the quarter height on the line joining from center of the base to the vertex.