Acceleration due to gravity at the surface of earth, g=R2GM=34πρGR.................(i)[∵M=34πR3ρ] Where, ρ= density of earth. Acceleration due to gravity at depth d from the surface of earth, g′=34πρG(R−d)...........(ii) From Eqs. (i) and (ii), we get g′=g[1−Rd]