Open Pipes and Vibrating Strings both have Lengths that are equal to one half of the wavelength for the fundamental. The next resonance occurs when there is a node in the middle of the pipe which means there is a complete wavelength in the pipe so the new wavelength is half of what it was for the fundamental. Since velocity=freq x wavelength and the velocity is constant, the frequency must have doubled.The answer must therefore be 600 Hz
For open pipes and strings, the harmonics occur at 2f, 3 f, 4f, 5f etc
For closed pipes the harmonics are 3f, 5f, 7f (notice no even harmonics)
