If the radius of the earth were increased by a factor of 2 keeping the mass constant by what factor would its density have to be changed to keep g the same?
g=GMR2=G(43πR3ρ)R2=43πGρRi.e.,g∝ρR
R is increased by a factor of 2 i.e., to keep the value of g to be constant the value of ρ has to be changed by a factor of 12.