Two satellites A and B go round a planet P

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Two satellites $A$ and $B$ go round a planet $ P$ in circular orbits having radii $4R$ and $R$ respectively. If the speed of the satellite $A$ is $3V$, the speed of the satellite $B$ will be ........ $V$

A

$12$

B

$6 $

C

$\frac{4}{3}$

D

$\frac{3}{2}$

Two satellites $A$ and $B$ go round a planet $ P$ in circular orbits having radii $4R$ and $R$ respectively. If the speed of the satellite $A$ is $3V$, the speed of the satellite $B$ will be ........ $V$

$v = \sqrt {\frac{{GM}}{R}} $

$\frac{{{v_A}}}{{{v_B}}} = \sqrt {\frac{{{R_B}}}{{{R_A}}}} = \sqrt {\frac{R}{{4R}}} = \frac{1}{2}$ 

$\frac{{{v_A}}}{{{v_B}}} = \frac{{3V}}{{{v_B}}} = \frac{1}{2}$

$\therefore \,\,{v_B} = 6\,V$