Question

radius of a planet is double than the radius of earth and its mass is 2 times then the mass of earth the weight of a 10 kg child on that planet will be

Answer 1

mass of earth =m
moss of the new planet =2m
radius of earth =r
radius of new planet =2r
now
gravity acting on earth =G*m /r^2
gravity acting on new planet =G*2m/(2r)^2
=G*2m/4r^2
gravity of earth /gravity of the new planet =(G*m/r^2)/(G*2m/4r^2)
=1/2
this means that the gravity acting on the new planet is twice the gravity acting on earth .
gravity acting on earth=9.8m/sec^2
gravity acting on new planet =2*9.8m/sec^2
=19.6m/sec^2
mass of child =10Kg
weight of child on new planet =mass of child * gravity acting on new planet
=10kg*19.6m/sec^2
=196newton