- Home
- Standard 11
- Physics
Two satellites of earth, $S_1$ and $S_2$ are moving in the same orbit. The mass of $S_1$ is four times the mass of $S_2.$ Which one of the following statements is true?
The potential energies of earth and satellite in the two cases are equal.
$S_1 $ and $S_2 $ are moving with the same speed
The kinetic energies of the two satellites are equal.
The time period of $S_1$ is four times that of $S_2.$
Solution
The satellite of mass $m$ is moving in a circular orbit of radius $r,$
$\therefore $ Kinetic energy of the satellite, $K = \frac{{GMm}}{{2r}}\,\,\,\,\,\,…\left( i \right)$
Potential energy of the satellite, $U = \frac{{ – GMm}}{r}\,\,\,\,\,…\left( {ii} \right)$
Orbital speed of satellite, $v = \sqrt {\frac{{GM}}{r}} \,\,\,\,\,…\left( {iii} \right)$
$Time – period\,of\,satellite,$
$\,T = {\left[ {\left( {\frac{{4{\pi ^2}}}{{GM}}} \right){r^3}} \right]^{1/2}}\,\,\,\,……\left( {iv} \right)$
$Given\,{m_{{s_1}}} = 4{m_{{s_2}}}$
Since $M,\, r$ is same for both the satellites ${S_1}\,and\,{S_2}$
$\therefore $ From equation $\left( {ii} \right)$ , we get $U \propto m$
$\therefore \frac{{{U_{{s_1}}}}}{{{U_{{s_2}}}}} = \frac{{{m_{{s_1}}}}}{{{m_{{s_2}}}}} = 4\,\,\,or,\,\,\,{U_{{s_1}}} = 4{U_{{s_2}}}$
Option $\left( a \right)$ is wrong.
From $\left( {iii} \right)$, since $v$ is independent of the mass of a satellite, the orbital speed is same for both satellites ${S_1}\,and\,{S_2}$.
Hence option $(b)$ is correct
From $(i)$, we get $K\, \propto m$
$\therefore \frac{{{K_{{s_1}}}}}{{{K_{{s_2}}}}} = \frac{{{m_{{s_1}}}}}{{{m_{{s_2}}}}} = 4\,\,or,\,\,{K_{{s_1}}} = 4{K_{{s_2}'}}$
Hence option $(c)$ is wrong.
From $(iv)$ , since $T$ is independent of the mass of a satellite, time period is same for both the satellites ${S_1}\,and\,{S_2}$ . Hence option $(d)$ is wrong.