There is a thick walled hollow cylinder (outer radius a, inner radius b). (z axis is the height of the cylinder) with its center located at the origin (x=0, y=0,z=0)
a) Find the gravitational potential of the cylinder at point P located on X axis?
b) Find the distance between point P and the origin is R. for R >> height and a, expand the integrand in powers of 1/R ( keep terms up to 1/R^3).