SOLUTION - Practice Doppler's Effect Problem 1 While passing by a bakery shop, two friends - each in their own car - are crossing each other on he road while driving. Friend I recognizes friend 2 in the other car and waves. Friend 2 realizes friend I was in the car that just passed, and he (friend 2) blows the car horn while the two friends continue on their opposite ways. If friend I is driving at a speed of 15m/s, and friend 2 is driving at a speed of 20m/s, and if the car horn emits a 350Hz sound, calculate: a) What is the frequency of the horn as heard by a person eating a muffin while sitting outside the bakery shop. Source (friend 2) moving away, listener ("air") standing: 344 m f = = 350Hz = 330.77Hz Icl + / us/ 344 + 20m b) What is the frequency of the horn as heard by friend 1. Listener (friend 1) moving away, source of frequency f' ("air") standing: f" =. 344m - 15 m Tel = 330.77Hz 344 m = 316.35Hz If the person who was sitting outside the bakery shop is done eating his muffin, and he starts running at 5m/s in the same direction as friend 2, calculate: c) What is now the frequency of the horn as heard by the person who was eating the muffin. Source (friend 2) moving away, listener ("air, " same as part a) standing: 344 m f = f Icl + |us/ = 350Hz 344m + 20 m = 330.77Hz Listener (man eating the muffin) moving toward the source ("air") of frequency f' standing: 344m + 5m f" = f = 330.77 Hz = 335.58Hz 344-m