Richard is preparing a mailing tube. Before he inserts his papers, he accidentally lets the mailing tube drop to the floor, and it produces a note. The mailing tube is 1.5 m long with a cylindrical cross section of 4-cm diameter. It is sealed at one end and open at the other. The speed of sound in air is 343 m/s at 20˚ C.
What is the frequency of the note that Richard heard?