Finding resonances?

Question

If the length of the tube is 4 meters, how many resonances would you observe when a tuning fork of frequency 256 Hz is used?

Answer 1

Zero. The air in the tube will oscillate at 256 Hz regardless of whether or not thats a resonant frequency if you excite it at a pure fixed frequency. That's why woodwinds use reeds, Being light and loose, they will oscillate in harmony at whatever frequencies the instrument resonates.

Answer 2

it depends whether tube is open at both ends or not

f=nv/2l for pipe open at both ends

f=(2n+1)v/4l for pipe closed at one end

f is frequency,v speed of sound,l length,n is a integer