Physics for IGCSE & O level - Waves And Sounds (Section 4 - No. 33)

What is the frequency of the ultrasound in Hz if the speed of sound in water is 1400 m/s and the wavelength is 0.035 m?

40 kHz

50 kHz

60 kHz

70 kHz

Using the wave equation (speed = frequency * wavelength): frequency = speed/wavelength = 1400 m/s / 0.035 m = 40000 Hz = 40 kHz