1.

The earth is assumed to be a sphere of radius R. A platform is arranged at a height R from the surface of the earth. The escape velocity ofa body from this platform is fv, where v is its escape velocity from the surface of the earth. The value of f is

Answer»

`1//2`
`sqrt(2)`
`1//sqrt(2)`
`1//3`.

Solution :Escape velocity of the body from the SURFACEOF earth is `V=sqrt(2R)`
Escape velocity of the body from the platform is fv.
`:." potential energy "+" kinetic energy "=0`
`-(GMM)/(2R)+(1)/(2)MV^(2)=0 rArr v=sqrt((GM)/(R^(2))).R=sqrt(gR)=fv`
From the surface of the earth, `v_("escape")=sqrt(2gR)`
`:. fv=(v_("escape"))/(sqrt(2)) rArr f=(1)/(sqrt(2))`.


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