(C) Given:Speed of the source (train),$v_s = 20 \, m \, s^{-1}$.Speed of sound in air,$v = 340 \, m \, s^{-1}$.Frequency of the source,$f_0 = 640 \, H

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(C) Given:Speed of the source (train),$v_s = 20 \, m \, s^{-1}$.Speed of sound in air,$v = 340 \, m \, s^{-1}$.Frequency of the source,$f_0 = 640 \, Hz$.Since the source is moving towards the stationary observer,the apparent frequency $f'$ is given by the Doppler effect formula:$f' = f_0 \left[ \frac{v}{v - v_s} \right]$Substituting the values:$f' = 640 \left[ \frac{340}{340 - 20} \right]$$f' = 640 \left[ \frac{340}{320} \right]$$f' = 640 \times 1.0625 = 680 \, Hz$.Thus,the frequency heard by the person is $680 \, Hz$.

Class 11 Physics Waves and Sound Doppler’s Effect

Difficult

$A$ train approaching a railway platform with a speed of $20 \, m \, s^{-1}$ starts blowing the whistle. The speed of sound in air is $340 \, m \, s^{-1}$. If the frequency of the emitted sound from the whistle is $640 \, Hz$,the frequency of sound as heard by a person standing on the platform is .... $Hz$.

A
$600$
B
$640$
C
$680$
D
$720$

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Class 11

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Waves and Sound

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Doppler’s Effect

$A$ train whistling at a constant frequency $n$ is moving towards a station at a constant speed $v_s$. The train goes past a stationary observer on the station. The frequency $n'$ of the sound as heard by the observer is plotted as a function of time $t$. Identify the correct curve.

DifficultKCET 2020

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The apparent frequency of a note,when a listener moves towards a stationary source with a velocity of $40 \ m/s$,is $200 \ Hz$. When the listener moves away from the same source with the same speed,the apparent frequency of the same note is $160 \ Hz$. The velocity of sound in air is (in $m/s$):

Medium

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$A$ policeman on duty detects a drop of $10 \%$ in the pitch of the horn of a moving car as it crosses him. If the velocity of sound is $330 \, m/s$,calculate the speed of the car in $m/s$.

Medium

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An observer moves towards a stationary source of sound with a speed $\frac{1}{5}^{\text{th}}$ of the speed of sound. The wavelength and frequency of the waves emitted by the source are $\lambda$ and $f$ respectively. The apparent frequency and wavelength heard by the observer are respectively,

MediumAP EAMCET 2019

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$A$ source and an observer move away from each other with the same velocity of $10 \,ms^{-1}$ with respect to the ground. If the observer finds the frequency of sound coming from the source as $1980 \,Hz$, then the actual frequency of the source is (speed of sound in air $= 340 \,ms^{-1}$). (in $\,Hz$)

MediumTS EAMCET 2023

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$A$ train whistling at a constant frequency $n$ is moving towards a station at a constant speed $v_s$. The train goes past a stationary observer on the station. The frequency $n'$ of the sound as heard by the observer is plotted as a function of time $t$. Identify the correct curve.

The apparent frequency of a note,when a listener moves towards a stationary source with a velocity of $40 \ m/s$,is $200 \ Hz$. When the listener moves away from the same source with the same speed,the apparent frequency of the same note is $160 \ Hz$. The velocity of sound in air is (in $m/s$):

$A$ policeman on duty detects a drop of $10 \%$ in the pitch of the horn of a moving car as it crosses him. If the velocity of sound is $330 \, m/s$,calculate the speed of the car in $m/s$.

An observer moves towards a stationary source of sound with a speed $\frac{1}{5}^{\text{th}}$ of the speed of sound. The wavelength and frequency of the waves emitted by the source are $\lambda$ and $f$ respectively. The apparent frequency and wavelength heard by the observer are respectively,

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