Physics 9702 · AS & A Level · Doppler effect for sound waves
Doppler effect for sound waves — practice question
A train moves at a constant high speed on a straight horizontal track towards an observer who is standing beside the track, as illustrated in Fig. 5.1. From $t = 0$ until it is well beyond the observer at time $t = t_2$, the train keeps sounding its horn continuously. The train goes past the observer at $t = t_1$. The horn produces a sound wave with constant frequency $f_s$.
(a)[1]
On Fig. 5.2, sketch how the frequency of sound heard by the observer changes with time $t$ from $t = 0$ to $t = t_2$.
(b)[3]
At a given instant, the sound waves at the observer have intensity $4.7 \times 10^{-3}\,\text{W m}^{-2}$. They arrive at right angles on to a circular detector with radius $2.8\,\text{cm}$. Calculate the power $P$ of the waves incident on the detector.
Worked solution & mark scheme
This 4-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Sketch with horizontal line above dashed line from $t=0$ to $t=t_1$, then below it from $t=t_1$ to $t=t_2$” …