Answer:
168 Hz, 280 Hz and 392 Hz
Explanation:
The resonant frequencies for a closed pipe at one end is given by :
[tex]f=\dfrac{nv}{4L}[/tex], n = 1,3,5...
The fundamental frequency, f₁ = v/4l = 56 Hz
For first overtone, put n = 3
[tex]f_3=\dfrac{3v}{4L}\\\\=3\times \dfrac{v}{4L}\\\\=3\times 56\\\\=168\ Hz[/tex]
For second overtone, put n = 5
[tex]f_5=5\times f_1\\\\=5\times 56\\\\=280\ Hz[/tex]
For third overtone, put n = 7
[tex]f_7=7\times f_1\\\\=7\times 56\\\\=392\ Hz[/tex]
So, the first three overtones are 168 Hz, 280 Hz and 392 Hz.