A body of mass of 20 kg is at rest on the earth's surface. (i) Find its gravitational potential energy. (ii) Find the kinetic energy to be provided to the body to make it free from the gravitational influenece of the earth.
`(g=9.8m//s^(2), R=6400km)`

Explanation

Data : `m=20kg, g=9.8m//s^(2),`
`R = 6400km=6.4xx10^(6)m`
(i) The gravitational potential energy of the of body = `-(GMm)/(R)=-mgR" "(because g=(GM)/(R^(2)))`
`=-20kgxx9.8m//s^(2)xx6.4xx10^(6)m`
`=-1.2544xx10^(9)J.`
(ii) To make the body free from the gravitational influence of the earth, it should be provided kinetic energy equal to `1.2544xx10^(6)J`.