A satellite of mass m is placed at a dista

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A satellite of mass $m$ is placed at a distance $r$ from the centre of earth (mass $M$). The mechanical energy of the satellite is

A

$ - \frac{{GMm}}{r}$

B

$\frac{{GMm}}{r}$

C

$\frac{{GMm}}{{2r}}$

D

$ - \frac{{GMm}}{{2r}}$

A satellite of mass $m$ is placed at a distance $r$ from the centre of earth (mass $M$). The mechanical energy of the satellite is

Mechanical energy $=K.E+U$ (kinetic energy $+$ potential energy)

$U=-\frac{G m M}{r}$

$K \cdot E=\frac{1}{2} m v^{2}$

$K . E=\frac{1}{2} \frac{G m M}{r}$

$M . E=K . E+U$

$=-\frac{G m M}{r}+\frac{1}{2} \frac{G m M}{r}$

$M . E=-\frac{G m M}{2 r}$