Doppler Effect

A train is moving on a straight track with speed $20 \mathrm{m} {\mathrm{s}}^{-1}$. It is blowing its whistle at the frequency of $1000 \mathrm{Hz}$. The percentage change in the frequency heard by a person standing near the track of the train as the train passes him is (speed of sound $=320 \mathrm{m} {\mathrm{s}}^{-1}$) close to

 A motorcycle starts from rest and accelerates along a straight path at $2 \mathrm{m} {\mathrm{s}}^{-2}$. At the starting point of the motorcycle, there is a stationary electric siren. How far has the motorcycle gone when the driver hears the frequency of the siren at $94\%$ of its value when the motorcycle was at rest? (speed of sound = $330 \mathrm{m} {\mathrm{s}}^{-1}$)

A police car with a siren of frequency $8 \mathrm{kHz}$ is moving with uniform velocity $36 \mathrm{km} {\mathrm{hr}}^{-1}$ towards a tall building which reflects the sound waves. The speed of sound in air is $320 \mathrm{m} {\mathrm{s}}^{-1}.$ The frequency of the siren heard by the car driver is

A source of sonic oscillations with frequency $f_0=1700$ $\mathrm{Hz}$ and a receiver are located on the same normal to a wall. Both the source and the receiver are stationary, and the wall recedes from the source with velocity $u=6.0$ $\mathrm{cm} {\mathrm{s}}^{-1}$. Find the beat frequency registered by the receiver. The velocity of sound is equal to $v=340$ $\mathrm{m} {\mathrm{s}}^{-1}$.

A source of sonic oscillations with frequency $f_0=1000 \mathrm{Hz}$, moves at right angles to the wall with a velocity $u=0.17$ $\mathrm{m} {\mathrm{s}}^{-1}$. Two stationary receivers $R_1$ and $R_2$ are located on a straight line, coinciding with the trajectory of the source, in the following succession: $R_1-$source$-R_2-$wall. Which receiver registers the beatings and what is the beat frequency? The velocity of sound is equal to $v=340 \mathrm{m} {\mathrm{s}}^{-1}$.

A road passes at some distance from a standing man. A truck is coming on the road with some acceleration. The truck driver blows a whistle of frequency $500 \mathrm{Hz}$when the line joining the truck and the man makes an angle $\mathrm{\theta }$ with the road. The man hears a note having a frequency of $600 \mathrm{Hz}$ when the truck is closest to him. Also the speed of truck has got doubled during this time. Find the value of $\mathrm{\theta }.$

A sonar system fixed in a submarine operates at a frequency $40 \mathrm{KHz}.$ An enemy submarine moves towards the sonar with a speed of $360 \mathrm{Km} {\mathrm{h}}^{-1}.$What is frequency (approximate) of sound received to sonar system, reflected by the submarine? Given :$V_{\mathrm{sound}}=1450 \mathrm{m} {\mathrm{s}}^{-1}$in water.

A band playing music at a frequency $f$ is moving towards a wall at a speed $v_b.$ A motorist is following the band with a speed $v_m.$ If $v$ is the speed of sound, obtain an expression for the beat frequency heard by the motorist .

Two observers A and B carry identical sound sources of frequency$256 \mathrm{Hz}.$If A is stationary while B moves away from A at a speed of $10 \mathrm{m}/\mathrm{s},$ how many beats per second are heard by A and B ?$(\mathrm{c} = 343 \mathrm{m}/\mathrm{s})$

A whistle producing sound waves of frequencies$9500 \mathrm{Hz}$and above is approaching a stationary person with speed $\mathrm{v} {\mathrm{ms}}^{–1}.$The velocity of sound in air is $300 {\mathrm{ms}}^{–1}.$ If the person can hear frequencies upto a maximum of $10,000 \mathrm{Hz},$the maximum value of $v$ upto which he can hear the whistle is:

In the figure shown an observer $O_1$ floats (static) on the water surface with ears in air while another observer $O_2$ is moving upwards with constant velocity$\mathit{ }{V}_1\mathit{=}\frac{\mathit{V}}{\mathit{5}}$ in water. The source moves down with constant velocity $V_{\mathit{s}}=\frac{V}{5}$ and emits the sound of frequency $f$. The velocity of sound in air is $V$ and that in water is $4V.$For the situation shown in figure: 

A girl stops singing a pure note. She is surprised to hear an echo of higher frequency, i.e., a higher musical pitch. Then:

Two vehicles $A$ and $B$ are moving towards each other with the same speed$u=25 \mathrm{m} {\mathrm{s}}^{-1}.$ They blow horns of the same frequency $f= 550 \mathrm{Hz}.$ Wind is blowing at speed $w=20 \mathrm{m} {\mathrm{s}}^{-1}$ in the direction of motion of $A$. The driver of vehicle $A$ hears the sound of the horn blown by vehicle $B$ and the sound of horn of his own vehicle after reflection from the vehicle $B$. If the difference of wavelength of both sounds received by $A$ is $\frac{5}{\mathit{ }P}$ . Find $P$. Velocity of sound is $=320 \mathrm{m} {\mathrm{s}}^{-1}.$

A man stands at rest in front of a large wall. A sound source of frequency$400 \mathrm{Hz}$ is placed between him and the wall. The source is now moved towards the wall at a speed of $1 \mathrm{m} {\mathrm{s}}^{-1}.$ The number of beats heard per second will be (speed of sound in air is $345 \mathrm{m} {\mathrm{s}}^{-1}$)

A source on a swing that is covering an angle $\mathrm{\theta }$ from the vertical is producing a frequency $v$. The source is distant $d$ from the place of support of swing. If the velocity of sound is $c$, acceleration due to gravity is $g$, then the maximum and minimum frequency heard by a listener in front of swing is

In the case of sound waves, the wind is blowing from source to receiver with speed $U_w$. Both source and receiver are stationary. If ${\lambda }_0$ is the original wavelength with no wind and $V$ is the speed of sound in the air then wavelength, as received by the receiver, is given by,

A train blowing its whistle moves with a constant velocity $v$ away from an observer on the ground. The ratio of the natural frequency of the whistle to that measured by the observer is found to be$1.2.$If the train is at rest and the observer moves away from it at the same velocity, this ratio would be given by:

A train moves towards a stationary observer with speed$34 {\mathrm{ms}}^{-1}.$The train sounds a whistle and its frequency registered by the observer is $f_1.$ If the train’s speed is reduced to $17 {\mathrm{ms}}^{-1},$the frequency registered is $f_2.$ If the speed of sound is 340m/s then the ratio$\frac{ f_1}{f_2}$is

An engine driver moving towards a wall with a velocity of $50 \mathrm{m} {\mathrm{s}}^{–1}$ emits a note of frequency $1.2 \mathrm{kHz}$. The frequency of note after reflection from the wall as heard by the engine driver when the speed of sound in air is $350 \mathrm{m} {\mathrm{s}}^{–1}$ is

Which of the following does not affect the apparent frequency in the Doppler effect?