Q78 / 90 · KVPY 2015 (SB/SX) · Physics

Two identical objects each of radii $R$ and masses $m_{1}$ and $m_{2}$ are suspended using two strings of equal length $L$ as shown in the figure $(R< < L)$. The angle $\theta$ which mass $\mathrm{m}_{2}$ makes with the vertical is approximatelyFigure

  • A
    $\frac{m_{1} R}{\left(m_{1}+m_{2}\right) L}$
  • Correct answer
    B
    $\frac{2 m_{1} R}{\left(m_{1}+m_{2}\right) L}$
  • C
    $[\mathrm] \frac{2 m_{2} R}{\left(m_{1}+m_{2}\right) L}$
  • D
    $\frac{m_{2} R}{\left(m_{1}+m_{2}\right) L}$

Solution

Figure
Distance of center of mass from $\mathrm{m}_{2}$ ? $$ \begin{array}{c} \mathrm{d}=\frac{m_{1}}{\left(m_{1}+m_{2}\right)} \times 2 R \\ \theta=\frac{\text { distance }(\mathrm{d})}{\mathrm{L}} \\ \theta=\frac{m_{1}}{\left(m_{1}+m_{2}\right)} \times \frac{2 R}{\mathrm{~L}} \end{array} $$

Hence, the correct answer is option: 'B'.

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