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7.Gravitation
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The change in potential energy when a body of mass $m$ is raised to height $n R$ from the earth's surface is ( $R$ is radius of earth)
A
$m g R\left(\frac{n}{n-1}\right)$
B
$n m g R$
C
$m g R\left(\frac{n}{n+1}\right)$
D
$m g R\left(\frac{n^2}{n^2+1}\right)$
Solution

(c)
Potential energy at the surface $=-\frac{G M m}{R}$
Potential energy at height, $n R=-\frac{G M m}{(n+1) R}$
Change in potential energy $=-\frac{G M m}{(n+1) R}+\frac{G M m}{R}$
$=\frac{G M m}{R}\left(\frac{-1+n+1}{n+1}\right)$
$=\left(\frac{n}{n+1}\right)\left(\frac{G M}{R^2}\right) m \times R$
$=m g R\left(\frac{n}{n+1}\right)$
Standard 11
Physics
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