1.

A small mass m is moved slowly from the surface of the earth to a height h above the surface. The work done (by an external agent) in doing this is

Answer»

mgh, for all VALUES of h
mgh, for `h LT lt R`
`1//2` MGR for h=R
`-1//2`mgR for h=R

Solution :`W=U_(2)-U_(1)=(GM m)/(R+h)-(-(GM m)/(R ))`
`=-GM m((1)/(R )-(1)/(R+h))=gR^(2)m[(h)/(R(R+h))]=(mgRh)/(R+h)`
For `h lt lt R`, W=mgh,
For h=R, `W=(mgR)/(2)`


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