Two uniform strings of mass per unit length $\mu$ and $4 \mu$, and length $L$ and 2 L , respectively, are joined at point $O$, and tied at two fixed ends $P$ and $Q$, as shown in the figure. The strings are under a uniform tension $T$. If we define the frequency $v_0=\frac{1}{2 L} \sqrt{\frac{T}{\mu}}$, which of the following statement (s) is (are) correct?