Physics - Sound Wave Question with Solution | TestHub

The formula for the frequency in an open organ pipe is 

$f=\frac{nv}{2L}$

Since, it is a second harmonic, $n=2$

The frequency of the second harmonic becomes $f=\frac{2v}{2L}=\frac{v}{L}$

The data given is 

$$\begin{gathered} L=0.4 \mathrm{m} \\ v=360 \mathrm{m} {\mathrm{s}}^{-1} \end{gathered}$$

Substituting the values in the frequency formula

$f=\frac{360 \mathrm{m} {\mathrm{s}}^{-1}}{0.4 \mathrm{m}}=900 \mathrm{Hz}$