Question

A stationary source sends forth monochromatic sound. A wall approaches it with velocity u = 33 cm/s. The propagation velocity of sound in the medium is v = 330 m/s. In what way and how much, in percent, does the wavelength of sound change on reflection from the wall?

Answer 1

Frequency of sound when it reaches the wall

wall will reflect the sound with same frequency v'. Thus frequency noticed by a stationary observer after reflection from wall

 since wall behaves as a source o f frequency v'.

Hence the sought percentage change in wavelength