Air is vibrating in a tube (closed at both ends) at its fundamental frequency of 160 Hz. If the tube is filled with helium instead, what is its fundamental frequency? Use 1020 m/s for the speed of sound in helium.

Answer 1

v(air) = lambda*fair

where lambda is the wavelength, fair is the frequency in air

v(helium) = lambda*fhelium

v(air)/v(helium) = f(air)/f(helium)

Look up the speed of sound in air and solve for f(helium)