Gce Model Questions Vol1 2020 Physics Question 3

Source \(S_{1}\) emits sound of frequency \(800\ \text{Hz}\) and moves directly towards a stationary observer with speed \(30\ \text{m s}^{-1}\). At the same time source \(S_{2}\) of frequency \(820\ \text{Hz}\) is fixed in position. The observer walks towards \(S_{2}\) with speed \(20\ \text{m s}^{-1}\). A large vertical wall is situated \(30\ \text{m}\) behind \(S_{2}\); the sound from \(S_{2}\) reflects off the wall before reaching the observer. The speed of sound in air is \(340\ \text{m s}^{-1}\). (a) Find the frequency heard from \(S_{1}\). (b) Find the frequency of the reflected wave from \(S_{2}\) that reaches the observer. (c) Find the beat frequency between the two sounds heard by the observer.