1.

The change in potential energy of the body when it is taken from the earth's surface to a height above its surface is :

Answer»

(n-1) mgR
nmgR
`(n)/(n+1)mgR`
`(n)/(n-1)mgR`

SOLUTION :At the surface of earth gravitational potential energy
`U_(1)=(-GMm)/(R)`
At HEIGHT nR from the surface of earth,
`U_(2)=(-GMN)/((n+1)R)`
`:.` Change in G.P.E is `Delta U=U_(2)-U_(1)`
`DeltaU=(-GMn)/((n+1)R)+(GMn)/(R)`
`DeltaU=(GMn)/(R)[1-(1)/(n+1)]=(GMn)/(R)((n)/(n+1))`
Since`g=(GM)/(R^(2))implies GM=gR^(2)`
`DeltaU=(gR^(2)m)/(R)((n)/(n+1))=(n)/(n+1)mgR`


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