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JEE Mains · Physics · STD 11 - Gravitation
  • JEE Mains 2024
  • Hard
  • MCQ

Two planets \(A\) and \(B\) having masses \(m_1\) and \(m_2\) move around the sun in circular orbits of \(r_1\) and \(r_2\) radii respectively. If angular momentum of \(\mathrm{A}\) is \(\mathrm{L}\) and that of \(B\) is \(3L\), the ratio of time period \(\left(\frac{T_A}{T_B}\right)\) is _______.

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Answer & Solution

Correct Answer

(C) \(\frac{1}{27}\left(\frac{m_2}{m_1}\right)^3\)

Step-by-step Solution

Detailed explanation

\(\frac{\pi \mathrm{r}_1^2}{\mathrm{~T}_{\mathrm{A}}}=\frac{\mathrm{L}}{2 \mathrm{~m}_1} \ldots \ldots . .(1)\)

\(\frac{\pi \mathrm{r}_2^2}{\mathrm{~T}_{\mathrm{B}}}=\frac{3 \mathrm{~L}}{2 \mathrm{~m}_2} \ldots \ldots .(2)\)

\(\Rightarrow \frac{\mathrm{T}_{\mathrm{A}}}{\mathrm{T}_{\mathrm{B}}}=3 \cdot \frac{\mathrm{m}_1}{\mathrm{~m}_2} \cdot\left(\frac{\mathrm{r}_1}{\mathrm{r}_2}\right)^2\)

\(\left(\frac{\mathrm{T}_{\mathrm{A}}}{\mathrm{T}_{\mathrm{B}}}\right)^2=\left(\frac{\mathrm{r}_1}{\mathrm{r}_2}\right)^3\)\(\Rightarrow\left(\frac{\mathrm{r}_1}{\mathrm{r}_2}\right)^2=\left(\frac{\mathrm{T}_{\mathrm{A}}}{\mathrm{T}_{\mathrm{B}}}\right)^{\frac{4}{3}}\)

\(\Rightarrow \frac{1}{27} \cdot\left(\frac{\mathrm{m}_2}{\mathrm{~m}_1}\right)^3=\left(\frac{\mathrm{T}_{\mathrm{A}}}{\mathrm{T}_{\mathrm{B}}}\right)\)

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