A light string is tied at one end to a fixed support and to a heavy string of equal length L at the other end A as shown in the figure (Total length of both strings combined is 2L). A block of mass M is tied to the free end of heavy string. Mass per unit length of the strings are $\mathrm{\mu }$ and 16$\mathrm{\mu }$ and tension is T. Find lowest positive value of frequency such that junction point A is a node.