A small source of sound is in uniform circular motion of radius R and angular speed π / 10 rad · s - 1 . It emits continuous sound of fixed frequency f 0 . A detector placed at a distance 2 R from the centre and in the plane of the circle records frequencies with maximum value 1200 Hz and minimum value 800 Hz . Take the speed of sound to be 330 m · s - 1 . Select the correct statement ( s ) .

The speed of source is 66 m · s - 1

EASY

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A car $P$ travelling at $20 m s^{- 1}$ sounds its horn at a frequency of $400 Hz$ . Another car $Q$ is travelling behind the first car in the same direction with a velocity $40 m s^{- 1}$ . The frequency heard by the passenger of the car $Q$ is approximately [Take, velocity of sound $= 360 m s^{- 1}$ ]

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Important Questions on Sound

HARD

Physics>Waves and Oscillations>Sound>Doppler Effect

If the source is moving away from the observer, then the apparent frequency ____.

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

Directions: Each of the following sentences in this section has a blank space and four words or group of words given after the sentence. Select the word or group of words you consider most appropriate for the blank space and indicate your response on the Answer Sheet accordingly.

Every rash driver becomes a ____ killer.

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

Two cars

X

and

Y

are approaching each other with velocities

36 km h^{- 1}

and

72 km h^{- 1}

respectively. The frequency of a whistle sound as emitted by a passenger in car

X,

heard by the passenger in car

Y

1320 Hz .

If the velocity of sound in air is

340 {ms}^{- 1},

the actual frequency of the whistle sound produced is ________

Hz .

HARD

Physics>Waves and Oscillations>Sound>Doppler Effect

A train is moving on a straight track with speed $20 m s^{- 1}$ . 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 (speed of sound $= 320 m s^{- 1}$ ) close to:

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

A submarine

A

travelling at

18 km {hr}^{- 1}

is being chased along the line of its velocity by another submarine

B

travelling at

27 km {hr}^{- 1}

B

sends a sonar signal of

500 H z

to detect

A

and receives a reflected sound of frequency

v

. The value of

v

is closed to (Speed of sound in water

1500 m s^{- 1}

)

EASY

Physics>Waves and Oscillations>Sound>Doppler Effect

When the source of sound moves towards a stationary observer, the wavelength of sound received by him

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

Two cars are approaching each other at an equal speed of

7.2 km {hr}^{- 1} .

When they see each other, both blow horns having a frequency of

676 Hz .

The beat frequency heard by each driver will be _______

Hz .

[Velocity of sound in air is

340 m s^{- 1}]

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

A musician using an open flute of length

50 cm

produces second harmonic sound waves. A person runs towards the musician from another end of a hall at a speed of

10 km h^{- 1}

. If the wave speed is

330 m s^{- 1}

, the frequency heard by the running person shall be close to

EASY

Physics>Waves and Oscillations>Sound>Doppler Effect

Two sentences are given below and you are required to find the correct sentence which combines both the sentences.

Which is the correct combination of the given two sentences?

He is too tired. He could not stand.

HARD

Physics>Waves and Oscillations>Sound>Doppler Effect

A train moving at

30 m s^{- 1}

is blowing a whistle with a frequency

500 Hz

. The speed of sound is

345 m s^{- 1}

. The wind is blowing with a speed

10 m s^{- 1}

in the direction of moving train. The apparent wavelengths of the whistle as heard by an observer who is respectively in front of and behind the train are

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

In the following sentence, a blank space with four options is given. Select whichever preposition or determiner you consider the most appropriate for the blank space.

These are the good rules to live _____.

HARD

Physics>Waves and Oscillations>Sound>Doppler Effect

Two men are walking along a horizontal straight line in the same direction. The man in front walks at a speed

1 .0 m s^{- 1}

and the man behind walks at a speed

2 .0 m s^{- 1}

. A third man is standing at a height

12 m

above the same horizontal line such that all three men are in a vertical plane. The two walking men are blowing identical whistles which emit a sound of frequency

1430 Hz

. The speed of sound in air is

330 m s^{- 1}

. At the instant, when the moving men are

10 m

apart, the stationary man is equidistant from them. The frequency of beats in

Hz

, heard by the stationary man at this instant, is __________.

EASY

Physics>Waves and Oscillations>Sound>Doppler Effect

A siren emitting a sound of frequency

800 Hz

moves away from an observer towards a cliff at a speed of

15 m s^{- 1}

. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is
(Take velocity of sound in air

= 330 m s^{- 1}

)

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

A small source of sound is in uniform circular motion of radius

R

and angular speed

π / 10 rad \cdot s^{- 1}

. It emits continuous sound of fixed frequency

f_{0}

. A detector placed at a distance

\sqrt{2} R

from the centre and in the plane of the circle records frequencies with maximum value

1200 Hz

and minimum value

800 Hz

. Take the speed of sound to be

330 m \cdot s^{- 1}

. Select the correct statement

(s)

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

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:

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

A bat moving at

10 m s^{- 1}

towards a wall sends a sound signal of

8000 Hz

towards it. On reflection, it hears a sound of frequency

f

. The value of

f

Hz

is close to

(speed of sound = 320 m s^{- 1})

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

A source of sound $S$ emitting waves of frequency $100 Hz$ and an observer $O$ are located at some distance from each other. The source is moving with a speed of $19.4 m s^{- 1}$ at an angle of $60^{o}$ with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer corresponding to the wave emitted by the source at the instant shown is

(velocity of sound in air $330 m s^{- 1}$ )

Question Image

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

A train approaching a railway crossing at a speed of

120 kmph

sounds a whistle of frequency

576 Hz

, when it is

288 m

away from the crossing. The frequency heard by the observer standing on the road perpendicular to the track from the crossing at a distance of

384 m

is (Speed of sound in air

= 340 m s^{- 1}

)

EASY

Physics>Waves and Oscillations>Sound>Doppler Effect

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with speed of

20 m s^{- 1}

with respect to the ground. If an observer in car A detects a frequency

2000 H z

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 m s^{- 1}

)

HARD

Physics>Waves and Oscillations>Sound>Doppler Effect

Two loudspeakers

M

and

N

are located

20 m

apart and emit sound at frequencies

118 Hz

and

121 Hz

, respectively. A car is initially at a point

P

1800 m

away from the midpoint

Q

of the line

M N

and moves towards

Q

constantly at

60 km h^{- 1}

along the perpendicular bisector of

M N

. 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

ν_{p}, ν_{Q} and ν_{R}

be the beat frequencies measured at locations

P, Q

and

R

, respectively. The speed of sound in air is

330 m s^{- 1} .

Which of the following statement(s) is (are) true regarding the sound heard by the person?

A car P travelling at 20 m s-1 sounds its horn at a frequency of 400 Hz. Another car Q is travelling behind the first car in the same direction with a velocity 40 m s-1. The frequency heard by the passenger of the car Q is approximately [Take, velocity of sound =360 m s-1]

Important Questions on Sound

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