A motorcyclist rides towards a high cliff at a constant speed of while continuously…
PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
A motorcyclist rides towards a high cliff at a constant speed of 18ms−1 while continuously sounding a horn that emits a steady note of frequency 540Hz. The sound reflected from the cliff reaches the rider and superposes with the direct sound from the horn.
(i) Taking the speed of sound in air to be 330ms−1, calculate the frequency of the sound received by the cliff.
(ii) The cliff acts as a reflecting surface and sends the sound back toward the motorcyclist. Determine the frequency of the reflected sound that finally reaches the rider.
(iii) Hence find the beat frequency heard by the motorcyclist while he is approaching the cliff.
(iv) Explain qualitatively how the beat frequency will change if the motorcyclist continues past the cliff and moves away from it at the same speed, keeping the horn on.