(B) According to the Doppler effect,the observed frequency $f$ is given by $f = f_0 \left( \frac{v}{v - v_s} \right)$,where $v$ is the speed of sound

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(B) According to the Doppler effect,the observed frequency $f$ is given by $f = f_0 \left( \frac{v}{v - v_s} \right)$,where $v$ is the speed of sound and $v_s$ is the speed of the source.For the first case,$v_s = 34\, m/s$,so $f_1 = f_0 \left( \frac{340}{340 - 34} \right) = f_0 \left( \frac{340}{306} \right)$.For the second case,$v_s = 17\, m/s$,so $f_2 = f_0 \left( \frac{340}{340 - 17} \right) = f_0 \left( \frac{340}{323} \right)$.Taking the ratio $f_1/f_2$:$\frac{f_1}{f_2} = \frac{f_0 (340/306)}{f_0 (340/323)} = \frac{323}{306}$.Dividing both by $17$,we get $\frac{323 \div 17}{306 \div 17} = \frac{19}{18}$.

Class 11 Physics Waves and Sound Doppler’s Effect

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$A$ train moves towards a stationary observer with speed $34\, m/s$. The train sounds a whistle and its frequency registered by the observer is $f_1$. If the speed of the train is reduced to $17\, m/s$,the frequency registered is $f_2$. If the speed of sound is $340\, m/s$,then the ratio $f_1/f_2$ is

JEE MAIN 2019 All JEE MAIN

A
$18/17$
B
$19/18$
C
$20/19$
D
$21/20$

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Waves and Sound

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Doppler’s Effect

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$A$ train sounding a whistle of frequency $510 \,Hz$ approaches a station at $72 \,km/hr$. The frequency of the note heard by an observer on the platform as the train $(1)$ approaches the station and then $(2)$ recedes from the station are respectively (in hertz) (velocity of sound in air $= 320 \,m/s$).

MediumMHT CET 2024

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$A$ vehicle sounding a whistle of frequency $256 \,Hz$ is moving on a straight road towards a hill with a velocity of $10 \,ms^{-1}$. The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 \,ms^{-1}$).

DifficultAP EAMCET 2005

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$A$ boy is walking away from a wall towards an observer at a speed of $1\, m/s$ and blows a whistle whose frequency is $680\, Hz$. The number of beats heard by the observer per second is (Velocity of sound in air $= 340\, m/s$).

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$A$ sound source is moving in a circle and an observer is outside the circle at $O$ as shown in the figure. If the frequencies as heard by the listener are $\nu_1, \nu_2$ and $\nu_3$ when the source is at positions $A, B$ and $C$ respectively,then:

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$A$ driver in a car,approaching a vertical wall,notices that the frequency of his car horn has changed from $440 \, Hz$ to $480 \, Hz$ when it gets reflected from the wall. If the speed of sound in air is $345 \, m/s,$ then the speed of the car is $....... \, km/hr$.

DifficultJEE MAIN 2020

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$A$ vehicle sounding a whistle of frequency $256 \,Hz$ is moving on a straight road towards a hill with a velocity of $10 \,ms^{-1}$. The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 \,ms^{-1}$).

$A$ boy is walking away from a wall towards an observer at a speed of $1\, m/s$ and blows a whistle whose frequency is $680\, Hz$. The number of beats heard by the observer per second is (Velocity of sound in air $= 340\, m/s$).

$A$ sound source is moving in a circle and an observer is outside the circle at $O$ as shown in the figure. If the frequencies as heard by the listener are $\nu_1, \nu_2$ and $\nu_3$ when the source is at positions $A, B$ and $C$ respectively,then:

$A$ driver in a car,approaching a vertical wall,notices that the frequency of his car horn has changed from $440 \, Hz$ to $480 \, Hz$ when it gets reflected from the wall. If the speed of sound in air is $345 \, m/s,$ then the speed of the car is $....... \, km/hr$.

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