Two planets of radii r1 and r2 are made from the same material. The ratio of the acceleration due to gravity g1g2 at the surface of the two planets is
Since they are made of the same material, therefore, the density of both the planets would be same.
Mass of the planet = volume x density (volume = 43π r3)
g1 = G×43πr13r12 and g2 = G×43πr23r22
On comparing both the ratio, we get, r1r2