Figure shows four tubes with lengths 1.0 m or 2.0 m, with one or two open ends as drawn. The third harmonic is set up in each tube, and some of the sound that escapes from them is detected by detector D, which moves directly away from the tubes. In terms of the speed of sound v, what speed must the detector have such that the detected frequency of the sound from

(a) Tube 1,

(b) Tube 2,

(c) Tube 3, and

(d) Tube 4 is equal to the tube's fundamental frequency?

3 4 2