A massless rod is suspended by two identical strings $AB$ and $CD$ of equal length. A block of mass $m$ is suspended from point $ O $ such that $BO$ is equal to $’x’$. Further, it is observed that the frequency of $1^{st}$ harmonic (fundamental frequency) in $AB$ is equal to $2^{nd}$ harmonic frequency in $CD$. Then, length of $BO$ is

815-16

  • A

    $\frac{L}{5}$

  • B

    $\frac{L}{4}$

  • C

    $\frac{4L}{5}$

  • D

    $\frac{3L}{4}$

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