Three sources of sound are distributed along a line, as shown in the figure. v i

Question

Three sources of sound are distributed along a line, as shown in the figure. v is the speed of sound. Sounce A is traveling at v/6 to the right, and it emits sound waves with a frequency of s40 Hz Source 8 is at rest, and it emits sound waves with a frequency of 3050 Hz. Source C is traveling at a speed of w's to the right, and it emits sound waves with a frequency of 1750 Hz. A, B, and C also detect the sound waves emitted by the other sources. All the questions below pertain to when the three sources of sound are at the locations shown in the figure below. at rest (a) what requency does A observe for the waves emitted by B(A = observer: B source) (D) what frequency does c observe for the waves em itted by A? (C·observer: A·Source) what frequency does B observe for the waves emitted by C? (B observer: Csource) (d) If 8 started moving to the right at just the right speed, B would observe a frequency for the waves it recelves from C that is exactly 1.5 times the frequency of the waves emitted by C. At what speed should 8 be moving so that B observes a frequency for the waves it receives from C that is exactly 1.5 times the frequency ef the waves emited by C?

Explanation / Answer

using doppler effect

part a )

here observer moving towards source

f' = (v+vo)*f/v

vo = v/6

f' = (v+v/6)*1050/v

f' = 1050*7/6

f' = 1225 Hz

part b )

observer is going away to source and source is moving towards observer

f' = (v-vo)*f/(v-vs)

f' = (v-v/8)*540/(v-v/6)

f' = 567 Hz

part c )

source is moving away from the observer

f' = f*v/(v+v/8)

f' = 1555.56 Hz

part d )

B is moving towards right

B observer and C source

observer moving to source and source moving away from observer

f' = (v+vo)*f/(v+vs)

f' = 1.5f

1.5 = (v+vo)/(v+v/8)

1.5 = (v+vo)/(9v/8)

13.5v = 8v + 8vo

5.5v = 8vo

vo = 5.5v/8 = 11v/16 = 11/16

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