Highschool Physics: frequency

Question

A musician is playing a song with various cups filled to different heights with water. She wants a particular glass to produce a sound wave of 520 Hz when struck. If the cup is 20.2 cm tall how high (in cm) should she fill it with water (the speed of sound in air is 340 m/s)?

Answer 1

velocity = wavelength x frequency

340 m/s = wavelength m x 520 sec^-1

wavelength = 340 m/s / 520 m = 0.654 m x 100 cm/m = 65.4 cm