Question

A spherical planet has twice the mass and twice the radius of the earth. if a man weighs 810 n on earth, what would his weight be on the surface of that planet?

Answer 1

Mass of person = 810/9.8 = 82.65   [where 9.8 is gravity on earth]

gravity on earth, g = GM/R²

gravity on given planet, g' = G(2M)/(2R)² = GM/2R²

g = 2g'

g' = 9.8/2 = 4.9

Weight of person on that planet = mg' = 82.65 * 4.9 = 405 N