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  • A source of sound is moving with constant velocity of 20 m/s emitting a note of frequency 1000 Hz. The ratio of frequencies observer by a stationary observer while the source is approching him and

A source of sound is moving with constant velocity of 20 m/s emitting a note of frequency 1000 Hz. The ratio of frequencies observer by a stationary observer while the source is approching him and after it  croses him will be (speed of sound \mathrm{}u=340 \; m/s)

Option: 1

9:8


Option: 2

8:9


Option: 3

1:1


Option: 4

9:10


Answers (1)

source is approaching the observer,

Frequency heard,

\mathrm{\begin{aligned} & n_a=\left(\frac{v}{v-v_s}\right) \times n \\ & n_a=\left(\frac{340}{340-20}\right) \times 1000 \\ & n_a=\frac{340}{320} \times 1000=1063 \mathrm{H} . \end{aligned}}-------(1)

when source is receding , the frequency heard

\mathrm{\begin{aligned} & n_r=\left(\frac{v}{r+v_s}\right) \times n \\ & n_r=\left(\frac{340}{340+20}\right) \times 1000 \\ & n_r=944 \mathrm{~Hz}-0 \end{aligned}} -----------(2)

So, \mathrm{\begin{aligned} & \frac{n_a}{n_r}=\frac{1063}{944} \\ & \frac{n_a}{h_r}=\frac{9}{8} \end{aligned}}

 

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Kshitij

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