First overtone of a closed organ pipe produces beats with first overtone of an open organ pipe with a beat frequency of $2 \mathrm{Hz}.$ Fundamental frequency of closed organ pipe is $55 \mathrm{Hz}.$ If frequency of open organ pipe exceeds that of closed organ pipe, then length of the open organ pipe is $n \mathrm{m}.$ Value of $n,$ is [Speed of sound in air is $330 \mathrm{m} {\mathrm{s}}^{-1}$]

A rod of mass $1.5 \mathrm{kg}$ and length $40 \mathrm{cm}$ is clamped with the help of two identical strings at the two ends as shown. A block of mass $5 \mathrm{kg}$ has to be connected on the rod. What should be the distance (in $\mathrm{cm}$ ) of point of suspension of block from the first end so that same tuning fork can vibrate the first string in second harmonic and the second string in third harmonic? $\left(g=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$