(8 points total) An observer can hear whistles from two identical trains. Train
ID: 1772120 • Letter: #
Question
(8 points total) An observer can hear whistles from two identical trains. Train #1 is moving away m/s, and Train #2 is moving towardthe observer at speed 8 m/s. is a cold frequency of each whistle is 100 Hz. from the observer at a speed of 8 It day and the speed of sound is 320 m/s. The unshifted (a) (3 points) What frequency does the observer hear f rom Train #1? Hz Frequency = (b) (3 points) what frequency does the observer hear from Train #2? Hz Frequency = (c) (2 points) What beat frequency does the observer hear? Hz Frequency =Explanation / Answer
Given,
v1 = 8 m/s ; v2 = 8 m/s ; vs = 320 m/s ; f = 100 Hz
We know from Doppler's shift
f = (V + Vr)/(V + Vs) x fo
a)Train 1 is receding so
f(receds) = f0 [vs/(vs + v1)]
f1(receds) = 100 x [320/(320 + 8)] = 97.56 Hz
Hence, f1 = 97.56 Hz
b)Train 2 is approaching so
f(approac) = f0[vs/(vs - v2)]
f(approac) = 100 [320/(320 - 8)] =102.56 Hz
Hence, f2 = 102.56 Hz
c)Beat frequency will be:
Fb = f2 - h1
Fb = 102.56 - 97.56 = 5 Hz
Hence, Fb = 5 Hz
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