Doppler Effect

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JEE Main 2020

The driver of a bus approaching a big wall notices that the frequency of his bus's horn changes from $420 Hz$ to $490 Hz$ , when he hears it after it gets reflected from the wall. Find the speed of the bus if speed of the sound is $330 ms^{- 1}$ .

81 kmh^{- 1}

(B)

91 kmh^{- 1}

(C)

71 kmh^{- 1}

(D)

61 kmh^{- 1}

LEVELJEE Main

An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

A stationary observer receives sound from two identical tuning forks, one of which approaches and the other one recedes with the same speed (much less than the speed of sound). The observer hears $2 beats/s$ . The oscillation frequency of each tuning fork is $ν_{0} = 1400 Hz$ and the velocity of sound in air is $350 m/s$ . The speed of each tuning fork is close to

(A)

\frac{1}{8} m/s

(B)

\frac{1}{2} m/s

(C)

1 m/s

(D)

\frac{1}{4} m/s

JEE Main 2021

LEVELJEE Main

Two cars are approaching each other at an equal speed of $7.2 km/h$ . When they see each other, both blow horns having frequency of $676 Hz$ . The beat frequency heard by each driver will be ......... $Hz$ . [Velocity of sound in air is $340 m/s$ .]

JEE Main 2019

LEVELJEE Main

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of $20 ms^{- 1}$ with respect to the ground. If an observer in car A detects a frequency $2000 Hz$ of the sound coming from car B, what is the natural frequency of the sound source in car B? (speed of sound in air = $340 ms^{- 1}$ )

(A)

2060 Hz

(B)

2250 Hz

(C)

2300 Hz

(D)

2150 Hz

JEE Main 2019

LEVELJEE Main

A musician produce the sound of second harmonics from open end flute of 50 cm. The other person moves toward the musician with speed 10 km/h from the second end of room. If the speed of sound 330 m/s, the frequency heard by running person will be

A submarine A travelling at $18 km/h$ is being chased along the line of its velocity by another submarine B travelling at $27 km/h$ . B sends a sonar signal of $500 Hz$ to detect A and receives a reflected sound of frequency $ν$ . The value of $ν$ is close to (Speed of sound in water $= 1500 ms^{- 1}$ )

(A)

504 Hz

(B)

507 Hz

(C)

499 Hz

(D)

502 Hz

JEE Main 2015

LEVELJEE Main

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

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 speed of sound is $340 m/s$ , then the ratio $f_{1} / f_{2}$ is

(A)

\frac{19}{18}

(B)

\frac{21}{20}

(C)

\frac{20}{19}

(D)

\frac{18}{17}

LEVELJEE Advanced

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

A stationary source emits sound waves of frequency $500 Hz$ . Two observers moving along a line passing through the source detect sound to be of frequencies $480 Hz$ and $530 Hz$ . Their respective speeds are in $ms^{- 1}$ , (Take, speed of sound $= 300 m/s$ )

A whistle producing sound waves of frequencies $9500 Hz$ and above is approaching a stationary person with speed $v ms^{- 1}$ . The velocity of sound in air is $300 ms^{- 1}$ . If the person can hear frequencies upto a maximum of $10000 Hz$ , the maximum value of $v$ upto which he can hear the whistle is

(A)

152 ms^{- 1}

(B)

15/ 2 ms^{- 1}

(C)

15 ms^{- 1}

(D)

30 ms^{- 1}

JEE Main 2020

LEVELJEE Advanced

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

(A)

54 km/h

(B)

36 km/h

(C)

18 km/h

(D)

24 km/h

JEE Main 2021

LEVELJEE Advanced

The frequency of a car horn encountered a change from 400 Hz to 500 Hz, when the car approaches a vertical wall. If the speed of sound is 330 m/s, then the speed of car is …… km/h.

JEE Main 2017

LEVELJEE Main

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency $10 GHz$ . What is the frequency of the microwave measured by the observer? (speed of light $= 3 \times 1 0^{8} ms^{- 1}$ )

(A)

12.1 GHz

(B)

17.3 GHz

(C)

15.3 GHz

(D)

10.1 GHz

JEE Main 2020

LEVELJEE Advanced

A sound source S is moving along a straight track with speed $v$ and is emitting sound of frequency $ν_{o}$ (see figure). An observer is standing at a finite distance, at the point O, from the track. The time variation of frequency heard by the observer is best represented by (Here, $t_{0}$ represents the instant when the distance between the source and observer is minimum.)

A source of sound S is moving with a velocity of $50 m/s$ towards a stationary observer. The observer measures the frequency of the source as $1000 Hz$ . What will be the apparent frequency of the source when it is moving away from the observer after crossing him? (Take, velocity of sound in air is $350 m/s$ )

(A)

807 Hz

(B)

1143 Hz

(C)

750 Hz

(D)

857 Hz

JEE Main 2019

LEVELJEE Main

Two sources of sound $S_{1}$ and $S_{2}$ produce sound waves of same frequency $660 Hz$ . A listener is moving from source $S_{1}$ towards $S_{2}$ with a constant speed $u m/s$ and he hears $10 beats/s$ . The velocity of sound is $330 m/s$ . Then, $u$ equal to

(A)

5.5 m/s

(B)

15.0 m/s

(C)

2.5 m/s

(D)

10.0 m/s

LEVELJEE Main

In hydrogen spectrum, the wavelength of $H_{α}$ line is $656 nm$ ; whereas in the spectrum of a distant galaxy $H_{α}$ line wavelength is $706 nm$ . Estimated speed of galaxy with respect to earth is

(A)

2 \times 1 0^{8} m/s

(B)

2 \times 1 0^{7} m/s

(C)

2 \times 1 0^{6} m/s

(D)

2 \times 1 0^{5} m/s

JEE Advanced 1996

LEVELJEE Main

A whistle emitting a sound of frequency $440 Hz$ is tied to a string of $1.5 m$ length and rotated with an angular velocity of $20 rad/s$ in the horizontal plane. Calculate the range of frequencies heard by an observer stationed at a large distance from the whistle. (Speed of sound = $330 m/s$ ).

JEE Advanced 1986

LEVELJEE Main

Two tuning forks with natural frequencies of $340 Hz$ each move relative to a stationary observer. One fork moves away from the observer, while the other moves towards him at the same speed. The observer hears beats of frequency $3 Hz$ . Find the speed of the tuning fork. Speed of sound = $340 m/s$ .

LEVELJEE Advanced

A train approaching a hill at a speed of $40 km/h$ sounds a whistle of frequency $580 Hz$ when it is at a distance of $1 km$ from a hill. A wind with a speed of $40 km/h$ is blowing in the direction of motion of the train. Find (a) the frequency of the whistle as heard by an observer on the hill, (b) the distance from the hill at which the echo from the hill is heard by the driver and its frequency. (Velocity of sound in air = $1200 km/h$ )

JEE Advanced 2011

LEVELJEE Main

A police car with a siren of frequency $8 kHz$ is moving with uniform velocity $36 km/h$ towards a tall building which reflects the sound waves. The speed of sound in air is $320 m/s$ . The frequency of the siren heard by the car driver is

(A)

8.50 kHz

(B)

8.25 kHz

(C)

7.75 kHz

(D)

7.50 kHz

JEE Advanced 2002

LEVELJEE Main

A siren placed at a railway platform is emitting sound of frequency $5 kHz$ . A passenger sitting in a moving train $A$ records a frequency of $5.5 kHz$ , while the train approaches the siren. During his return journey in a different train $B$ he records a frequency of $6.0 kHz$ while approaching the same siren. The ratio of the velocity of train $B$ to that of train $A$ is

(A)

\frac{242}{252}

(B)

(C)

\frac{5}{6}

(D)

\frac{11}{6}

JEE Advanced 2010

LEVELJEE Advanced

A stationary source is emitting sound at a fixed frequency $f_{0}$ , which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is $1.2%$ of $f_{0}$ . What is the difference in the speeds of the cars (in km per hour) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound which is $330 ms^{- 1}$ .