A device that both emits and receives sound waves is traveli

A device that both emits and receives sound waves is traveling at 64 km/h . The emitted waves have a frequency of 770 Hz . Part A If the waves are reflected off a stationary flat surface in front of the device, what frequency is detected by the device?

Solution

using doppler effect,

f = (v + Vr) f0 / (v + Vs)

v =speed of sound , Vr = reciever speed (+ve if moving towards the source)

Vs = source speed (+ve if source is moving away from reciever)

v = 64 km/h = 64 x 1000m / 3600sec = 17.78 m/s

frequency of reflected wave f\' = ( 343 + 0) 770 / (343 - 17.78) = 812.10 Hz

now for reciever,

final f = (343 + 17.78)770 / (343 +0) = 809.91 Hz