Question

How much energy will be necessary for making a body of 500 kg escape from the earth
`[g=9.8 ms^(2)," radius of earth "=6.4xx10^(6)m]`
A. `6.4xx10^(8)J`
B. `3.2xx10^(10)J`
C. `6.4xx10^(12)J`
D. `3.2xx10^(6)J`

Answer 1

Correct Answer - B
P.E. of the ody at the surface of the earth,
`U=-(GMm)/(R )` but `g=(GM)/(R^(2)) therefore (GM)/(R )=gR`
`=-(3.2xx10^(10)J)`
Thus an energy of `3.2xx10^(10)J` should be given to the body in the form of K.E., so that it will escape from the earth.