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A person riding on a source ' $S$ ' of sound (frequency $48 Hz$ ) moves in a medium (in which velocity of sound is $310 m s^{- 1}$ ) with speed $10 m s^{- 1}$ as shown towards a liquid reservoir (in which velocity of sound is $1240 m s^{- 1}$ ). A detector ' $D$ ' in the reservoir moves towards the free surface of the reservoir (along line $S D$ ) at a speed $20 m s^{- 1}$ . The sound produced by ' $S$ ' gets reflected and transmitted at the free surface. Mark the INCORRECT statement(s) among the following, assuming the liquid in the reservoir stays still and calm.

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Important Questions on Mechanical Wave

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

Two vibrating strings '

A

' and '

B

' produce beats of frequency

8 Hz

. The beat frequency is found to reduce to

4 Hz

if the tension in the string

' A'

is slightly reduced. If the original frequency of

A

320 Hz

, then the frequency of

B

' is

EASY

Physics>Mechanics>Mechanical Wave>Beats

A source of sound gives

5

beats per second when sounded with another source of frequency

100 s^{- 1} .

The second harmonic of the source together with a source of frequency

205 s^{- 1}

gives

5

beats per second. The frequency of the source is

EASY

Physics>Mechanics>Mechanical Wave>Beats

Two sound waves with wavelengths

5.0 m

and

5.5 m

, respectively, each propagates in gas with velocity

330 m s^{- 1}

. The number of beats that can be expected from them per second is

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

The velocity of sound in a gas, in which two wavelengths

4.08 m

and

4.16 m

produce

40

beats in

12 s

, will be

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

The correct figure that shows, schematically, the wave pattern produced by the superposition of two waves of frequencies

9 H z

and

11 H z

, is

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

A source of sound emitting at a frequency

f

is moving towards a wall with speed

v_{b}

. If

v

is the speed of sound then the beat frequency heard by a stationary observer behind the source is

EASY

Physics>Mechanics>Mechanical Wave>Beats

A tuning fork

A

of unknown frequency produces

5 beats s^{- 1}

with a fork of known frequency

340 Hz

. When fork

A

is filed, the beat frequency decreases to

2 beats s^{- 1}

. What is the frequency of fork

A

HARD

Physics>Mechanics>Mechanical Wave>Beats

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>Mechanics>Mechanical Wave>Beats

In a guitar, two strings

A

and

B

made of same material are slightly out of tune and produce beats of frequency

6 Hz

. When tension in

B

is slightly decreased, the beat frequency increases to

7 Hz

. If the frequency of

A

530 Hz

, the original frequency of

B

will be:

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

A closed organ pipe and an open organ pipe of same length produce

2 beats \sec^{- 1}

when they are set into vibrations together in fundamental mode. The length of open pipe is now halved and that of closed pipe is doubled. The number of beats produced will be

EASY

Physics>Mechanics>Mechanical Wave>Beats

A set of

20

tuning forks is arranged in a series of increasing frequencies. If each fork gives

4

beats with respect to the preceding fork and the frequency of the last fork is twice the frequency of the first, then the frequency of last fork is _____

Hz

EASY

Physics>Mechanics>Mechanical Wave>Beats

Three sound waves of equal amplitudes have frequencies,

(n - 1), n, (n + 1)

. They superimpose to give beats. The number of beats produced per second will be

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

An observer is riding on a bicycle and moving towards a hill at

18 km h^{- 1}

. He hears a sound from a source at some distance behind him directly as well as after its reflection from the hill. If the original frequency of the sound as emitted by source is

640 Hz

and velocity of the sound in air is

320 m s^{- 1}

, the beat frequency between the two sounds heard by observer will be _____

Hz

EASY

Physics>Mechanics>Mechanical Wave>Beats

Two tuning forks have frequencies

450 Hz

and

454 Hz

respectively. On sounding these forks together, the time interval between two successive maximum intensities will be _______.

EASY

Physics>Mechanics>Mechanical Wave>Beats

A tuning fork vibrates with frequency

256 Hz

and gives one beat per second with the third normal mode of vibration of an open pipe. What is the length of the pipe? (speed of sound in air is

340 m s^{- 1}

)

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

The frequency of two tuning forks

A

and

B

are

1.5 %

more and

2.5 %

less than that of the tuning fork

C

. When

A

and

B

are sounded together,

12

beats are produced in

1

second. The frequency of tuning fork

C

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

A toy-car, blowing its horn, is moving with a steady speed of

5 m s^{- 1}

, away from a wall. An observer, towards whom the toy car is moving, is able to hear

5

beats per second. If the velocity of sound in air is

340 m s^{- 1}

the frequency of the horn of the toy car is close to

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

Two sitar strings,

A

and

B

playing the note '

D h a

' are slightly out of tune and produce beats of frequency

5 Hz

. The tension of the string

B

is slightly increased and the beat frequency is found to decrease by

3 Hz

. If the frequency of

A

425 Hz

. The original frequency of

B

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

Two waves of wavelength 99 cm and 100 cm both travelling with velocity

396 m s^{- 1}

are made to interface. The number of beats produced by them per second are

MEDIUM

Physics>Mechanics>Mechanical Wave>Beats

A tuning fork of known frequency 256 Hz makes 5 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per second when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was

Important Questions on Mechanical Wave

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