# Apparent Frequency:Listener Moving

## Trending Questions

**Q.**

The driver of a bus approaching a big wall notices that the frequency of his bus’s horn changes from $420Hzto490Hz$ when he hears it after it gets reflected from the wall. Find the speed of the bus if the speed of the sound is $330m{s}^{-1}$.

$81km/h$

$91km/h$

$71km/h$

$61km/h$

**Q.**Two sources P and Q produces notes of frequency 990 Hz each. A listener moves from P to Q with a speed of 1 ms−1. If the speed of sound is 330 m/s, then the number of beats heard by the listener per second is

- 4
- 5
- 6
- 7

**Q.**The frequency of a tuning fork is 384 Hz and velocity of sound in air is 352 ms−1. How far sound has travelled when fork completes 36 vibrations?

- 33 m
- 16.5 m
- 11 m
- 22 m

**Q.**A man standing on a platform observes that the frequency of the sound of a whistle emitted by a moving train is less by 140 Hz that the frequency emitted when the train is stationary. If the velocity of sound in air is 330 m/s and the speed of the train is 70 m/s, the frequency of the whistle is

- 571 Hz
- 800 Hz
- 400 Hz
- 260 Hz

**Q.**The engine of a train sounds a whistle at frequency (f). The frequency heard by a passenger is

- 1f
- >f
- f
- <f

**Q.**Two cars moving in opposite directions approach each other with speeds of 40 ms−1 and 50 ms−1 respectively. The driver of the first car blows a horn of frequency 400 Hz. The frequency heard by the driver of the second car is

[speed of sound =340 ms−1]

- 515 Hz
- 375 Hz
- 520 Hz
- 450 Hz

**Q.**Two tuning forks with natural frequencies 340 Hz each move relative to 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 (velocity of sound in air is 340 m/s).

- 1.5 m/s
- 3 m/s
- 4.5 m/s
- 6 m/s

**Q.**A stationary observer receive 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 per second. The oscillation frequency of each tuning fork is f0=1400 Hz and the velocity of sound in air is 350 ms−1. The speed of each tuning fork is close to:

- 12 ms−1
- 1 ms−1
- 14 ms−1
- 18 ms−1

**Q.**

Figure (16-E111)shows a person standing somehere in between two identical tuning forks, each vibrating at

512 Hz. If both the tuning forks move towards right at a speed of 5.5 m s^{-1}, find the number of beats heard by the listener. Speed of sound in air =330ms−1.

**Q.**Two loudspeakers M and N are located 20 m apart and emit sound at frequencies 118 Hz and 121 Hzrespectively. A car is initially at a point P, 1800 m away from the midpoint Q of the line MN and moves towards Q constantly at 60 km/hr along perpendicular bisector of MN. It crosses Q and eventually reaches a point R, 1800 m away from Q. Let ν(t) represent the beat frequency measured by a person sitting in the car at time t. Let νp, νQ and νR be the beat frequencies measured at locationsP, Q and R, respectively. The speed of sound in air is 330 ms−1. Which of the following statement (s) is (are) true regarding the sound heard by the person?

- A plot below represents schematically the variation of beat frequency with time

- The rate of change in beat frequency is maximum when the car passes through Q
- νP+νR=2νQ
- The plot below represents schematically the variation of beat frequency with time

**Q.**An observer move towards a stationary source of sound with a velocity equal to one fifth of the velocity of sound. The apparent change in frequency is

- 35%
- 30%
- 25%
- 20%

**Q.**An observer travelling with a constant velocity of 20 ms−1 passes close to a stationary source of sound and notices that there is a change of frequency of 50 HZ as he passes the source. What is the frequency of the source? Speed of sound in air = 340 m/s.

- 450 Hz
- 400 Hz
- 425 Hz
- 500 Hz

**Q.**

A traffic policeman sounds a whistle to stop a car-driver approaching towards him. The car-driver does not stop and takes the plea in court that because of the Doppler shift, the frequency of the whistle reaching him might have gone beyond the audible limit of 20 kHz and he did not hear it. Experiments showed that the whistle emits a sound with frequency close to 16 kHz. Assuming that the claim of the driver is true, how fast was he driving the car ? Take the speed of sound in air to be 330ms−1. Is this speed practical with today's technology ?

**Q.**A train standing at a certain distance from a railway platform is blowing a whistle of frequency 500 Hz. If the speed of sound is 340 ms−1, the frequency and wavelength of the sound of the whistle heard by a man running towards the engine with a speed of 10 ms−1 respectively are

- 500 Hz, 0.7 m
- 500 Hz, 0.68 m
- 486 Hz, 0.7 m
- 515 Hz, 0.68 m

**Q.**A train moves towards a stationary observer with a speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is f1. If the speed of the train is reduced to 17 m/s, the frequency registered is f2. If the speed of sound is 340 m/s , then the ratio f1f2 is

[Assume, medium is stationary ]

- 1819
- 12
- 2
- 1918

**Q.**

Two identical tuning forks vibrating at the same frequency 256 Hz are kept fixed at some distance apart. A listener runs between the forks at a speed of 3.0 m/s so that he approaches one tuning fork while receding from the other (figure). Find the beat frequency observed by the listener. Speed of sound in air = 332 m/s.

4.6

5.6

5.2

4.2

**Q.**

A bullet passes past a person at a speed of 220 m/s. Find the fractional change in the frequency of the whistling sound heard by the person as the bullet crosses the person. Speed of sound in air =330 m/s.

**Q.**A police car with a siren of frequency 9 kHz is moving with uniform velocity 75 km/hr towards a tall building which reflect the sound wave. The speed of sound in air is 340 m/s. The frequency of siren heard by the car driver is

- 8 kHz
- 10 kHz
- 2 kHz
- 14 kHz

**Q.**A source moves towards a stationary observer with speed 40 m/s. The source sounds a whistle and its frequency registered by the observer is n1. If the source's speed is reduced to 20 m/s, the frequency registered is n2. If the speed of sound is 340 m/s, then the ratio f1f2is

[Assume, medium is stationary]

- 54
- 1516
- 1615
- 45

**Q.**Two sound sources shown in the figure vibrate in phase. By moving S1 along PS1 consecutive minima are heard when L1−L2 has values, 20 cm , 60 cm and 100 cm. If the frequency of sound source is 1700n Hz. Then find the value of n : [Speed of sound is 340 m/s ]

**Q.**Two bikes moving in opposite directions approach each other with speed of 40 m/s and 20 m/s respectively. The first bike sounds a horn having a frequency 380 Hz. The frequency heard by the biker of the second bike is

[velocity of sound in air is 340 m/s]

- 450 Hz
- 460 Hz
- 456 Hz
- 465 Hz

**Q.**

A traffic policeman standing on a road sounds a whistle emitting the main frequency of 2.00 kHz. What could be the appparent frequency heard by a scooter-driver approaching the policeman at a speed of 36.0 km/h ? Speed of sound in air = 340 m/s.

**Q.**A fixed source of sound emitting a certain frequency appears as fa when the observer is approaching the source with speed v0 and fr when the observer recedes from the source with the same speed. The frequency of the source is

- fr+fa2
- fr−fa2

- √fafr

- 2frfafr+fa

**Q.**

An observer moves towards a stationary source of sound, with a velocity ${\frac{1}{5}}^{th}$ of the velocity of sound. What is the $\%$ increase in the apparent frequency?

Zero

$0.5\%$

$5\%$

$20\%$

**Q.**A train is travelling at 120 kmph and blows a whistle of frequency 1000 Hz. The frequencies of the sound heard by a stationary observer, if the train is approaching him and moving away from him are:

[(Velocity of sound in air =330 m/s and assume medium is stationary]

- 91 Hz−111 Hz
- 908 Hz−1112 Hz
- 82 Hz−110 Hz
- 820 Hz−1080 Hz

**Q.**

A person riding a car moving at 72 km/h sounds a whistle emitting a wave of frequency 1250 Hz. What frequency will be heard by another person standing an the road (a) in front of the car (b) behind the car ? Speed of sound in air = 340 m/s.

**Q.**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 speed of the car is

- 54 km/hr
- 36 km/hr
- 18 km/hr
- 24 km/hr

**Q.**A source of sound emits sound waves at frequency f0. It is moving towards an observer with fixed speed vs (vs<v, where v is the speed of sound in air). If the observer were to move towards the source with speed v0, one of the following two graphs (A and B) will give the correct variation of the frequency f heard by the observer as v0 is changed.

The variation of f with v0 is given correctly by:

- graph A with slope = f0(v+vs)
- graph A with slope = f0(v−vs)
- graph B with slope = f0(v−vs)
- graph B with slope = f0(v+vs)

**Q.**A source of sound S has a frequency f. Wind is blowing from source to observer O with velocity u. If speed of sound with respect to air is C, the wavelength of sound detected by O is:

- C+uf
- C(C+u)(C−u)f
- C−uf
- Cf

**Q.**A source of sound producing sound of frequency f is at rest. An observer starts moving toward it at t=0 with a constant small acceleration. Which of the following graph best represents the variation of observed frequency f′ recorded by the observer with time t?