On a planet whose size is the same and mass 4 times as that of the Earth, find the amount of energy needed to lift a 2 kg mass vertically upwards through a distance 3 m of the planet. (value of g on the surface of th Earth is `10m//sec^(2)`).

Explanation

On the surface of the Earth,
`g=(GM)/(R^2)`
On the planet,
`g'=(Gxx4M)/(R^2)`
`therefore(g')/(g)=4`
(or) `g'=4g=40m//s^(2)`
Energy needed to lift the body
`=mg'h`
`=2xx40xx3`
`=240"Joules"`