A stationary source sends forth monochromatic sound. A wall approaches it with velocity 33 cm/s. The propagation velocity of sound in the medium is `c=330(m)/(s)`. How much, in per cent , does the wavelength of sound change on reflection from the wall?

Explanation

When a reflector moves towards the source
`lamda'=(c-u)/(c+u)lamda`
or `(lamda'-lamda)/(c+u)=-(2u)/(c+u)`
The negative sign shows that the wavelength decreases.
`%`decrease`=(2uxx100)/(c+u)=(2xx0.33xx100)/(330+0.33)`
`=0.2`