Class 9 - foundation physics (Sound)Contact Number: 9667591930 / 8527521718

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1.

If the period of small ripples on the water is 0.1s and their wavelength is 5 cm, what is the speed of the wave?

2.

A wave pulse on a string moves a distance of 8m in 0.05s.

(a) Find the velocity of the pulse.

(b) What would be the wavelength of the wave on the same string if its frequency is 200 Hz?

3.

The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

4.

25 waves pass through a point in 5 seconds. If the distance between one crest and the adjacent trough is 0.05, calculate

(a) The frequency

(b) The wavelength

(c) Wave velocity

5.

$\mathrm{How}\mathrm{fast}\mathrm{will}\mathrm{a}\mathrm{wave}\mathrm{travel}\mathrm{in}\mathrm{air}\mathrm{at}\mathrm{a}\mathrm{temprature}\mathrm{of}15\xb0\mathrm{C}.$

6.

A snapshot is taken of a periodic wave traveling on a string as shown below. What is the amplitude and wavelength of the wave?

7.

a wave on a string has a frequency of 440 Hz and a wavelength of 1.3m. How fast does the wave travel?

8.

$\left(\mathrm{a}\right)\mathrm{Speed}\mathrm{of}\mathrm{sound}\mathrm{in}\mathrm{air}\mathrm{is}332\mathrm{m}/\mathrm{s}\mathrm{at}\mathrm{NTP}.\mathrm{What}\mathrm{wil}\mathrm{be}\mathrm{the}\mathrm{speed}\mathrm{of}\mathrm{sound}\mathrm{in}\mathrm{hydrogen}\mathrm{at}\mathrm{NTP}\mathrm{if}\mathrm{the}\mathrm{density}\mathrm{of}\mathrm{hrdrogen}\mathrm{at}\mathrm{NTP}\mathrm{is}\left(1/16\right)\phantom{\rule{0ex}{0ex}}\mathrm{that}\mathrm{of}\mathrm{air}?\phantom{\rule{0ex}{0ex}}\left(\mathrm{b}\right)\mathrm{Calculate}\mathrm{the}\mathrm{ratio}\mathrm{of}\mathrm{the}\mathrm{speed}\mathrm{of}\mathrm{sound}\mathrm{in}\mathrm{neon}\mathrm{to}\mathrm{that}\mathrm{in}\mathrm{water}\mathrm{vapour}\mathrm{at}\mathrm{any}\mathrm{temprature}.\phantom{\rule{0ex}{0ex}}\left[\mathrm{Molecular}\mathrm{weight}\mathrm{of}\mathrm{neon}=2.02\mathrm{x}{10}^{-2}\mathrm{kg}/\mathrm{mol}\mathrm{and}\mathrm{for}\mathrm{water}\mathrm{valours}=1.8\mathrm{x}{10}^{-2}\mathrm{kg}/\mathrm{mol}\right]$

9.

$\mathrm{The}\mathrm{velocity}\mathrm{of}\mathrm{sound}\mathrm{in}\mathrm{hydrogen}\mathrm{at}0\xb0\mathrm{C}\mathrm{is}1200\mathrm{m}/\mathrm{s}.\mathrm{When}\mathrm{some}\mathrm{amount}\mathrm{of}\mathrm{oxygen}\mathrm{is}\mathrm{mixed}\mathrm{with}\mathrm{hedrogen},\mathrm{the}\mathrm{velocity}\mathrm{decreases}\mathrm{to}\phantom{\rule{0ex}{0ex}}500\mathrm{m}/\mathrm{s}.\mathrm{Determine}\mathrm{the}\mathrm{ratio}\mathrm{of}{\mathrm{H}}_{2}\mathrm{to}{\mathrm{O}}_{2}\mathrm{by}\mathrm{volume}\mathrm{in}\mathrm{this}\mathrm{mixture},\mathrm{given}\mathrm{that}\mathrm{the}\mathrm{density}\mathrm{of}\mathrm{oxygen}\mathrm{is}16\mathrm{times}\mathrm{that}\mathrm{of}\mathrm{hydrogen}.$

10.

A man stands in between two cliffs x and y, such that he is at a distance Of 66m from x. When he blows a whistle he hears first echo after 0.4s and second echo after 1.2s. Calculate:

(i) speed of sound

(ii) the distance of cliffy from man.

11.

A road mid-way between two parallel rows of building. A motorist moving with a speed of 36 km/hr. sounds the horn. Find the distance between the two rows of buildings. When will he hear the echo sound time? The velocity of sound in air is 330 m/sec.

12.

The length of a sonometer wire between two fixed ends in 1.10m. Where should the two bridges be placed to divide the wire into three segments whose fundamental frequencies are in the ratio of 1:2:3?

13.

For a certain organ pipe, three successive resonance frequencies are observed at 425, 595, and 765 Hz respectively. Taking the speed for sound in air to be 340 m/s

(a) Explain whether the pipe is closed at one or open at both ends

(b) Determine the fundamental frequency and length of the pipe.

14.

A column of air and a tuning fork produces 4 beats per second when sounded together. The tuning fork gives the lower note. The temperature of the air is $15\xb0\mathrm{C}$. When the temperature falls to $10\xb0\mathrm{C}$, the two produce 3 beats per second. Find the frequency of the tuning fork.

15.

A string of length 25cm 2nd mass 2.5 g is under tension. A pipe closed at one end is 40 cm long. When the string is set vibrating in its first overtone and the in the pipe in its fundamental frequency, 8 beats per second are heard. It is observed that decreasing the tension in the string decreases the beat frequency. If the speed of sound in air is 320 ${\mathrm{ms}}^{-1}$, find the tension in the string.

16.

tuning forks A and B sounded together to give 6 beats per second. With an air resonance tube closed at one end, the two forks give resonance when the two air columns are 24 cm and 25 cm respectively. Calculate the frequencies of forks.

17.

A train approaching a hill at a speed of 40km/h sounds a whistle of frequency 580 Hz when it is at a distance of 1km from a hill. A wind with a speed of 40Km/hr. is blowing in the direction of the motion of the train. Find the frequency of the whistle as heard by an observer on the hill. (velocity of sound in air = 1200 km/h

18.

A source of the sound of frequency 256Hz is moving rapidly towards a wall with a velocity of 5m/s. How many beats per second will be heard if sound travels at a speed of 330 m/s by an observer behind the source?

19.

A siren is fitted on a car going towards a vertical wall at a speed of 36 km/hr A person standing on the ground, behind the car, listens to the siren sound coming directly from the source as well as that coming after reflection from the w Calculate the apparent frequency of the wave (a) coming directly from the siren to the person and (b) coming a reflection. Take the speed of sound to be 340 m/s.

20.

$\mathrm{A}\mathrm{particle}\mathrm{in}\mathrm{SHM}\mathrm{is}\mathrm{described}\mathrm{by}\mathrm{the}\mathrm{displacement}\mathrm{equation},\mathrm{x}=\mathrm{A}\mathrm{sin}\left(\mathrm{\omega t}+\mathrm{\varphi}\right);\mathrm{\omega}=\frac{2\mathrm{\pi}}{\mathrm{T}}.\mathrm{If}\mathrm{at}\mathrm{t}=0,\mathrm{position}\mathrm{of}\mathrm{particle}\mathrm{is}1\mathrm{cm}\mathrm{and}\phantom{\rule{0ex}{0ex}}\mathrm{its}\mathrm{iitial}\mathrm{velocity}\mathrm{is}\mathrm{\pi}{\mathrm{cms}}^{-1},\mathrm{find}\mathrm{its}\mathrm{amplitude}\mathrm{initial}\mathrm{phase}.\mathrm{The}\mathrm{frequency}\mathrm{is}\frac{1}{2}{\mathrm{s}}^{-1}.$

21.

A simple harmonic motion is represented by $\mathrm{x}=5\mathrm{sin}\left(10\mathrm{t}+\mathrm{\pi}/4\right).$ Write its amplitude, angular frequency, frequency, period and initial phase. Displacement is in meters and time in seconds.

22.

A particle executes SHM with amplitude 20 cm and time period 4s. find the minimum time required for the particle to move between two points 10 cm on either side of the mean position.

23.

A narrow pulse (for example, a short pip by a whistle) is sent across a medium.

(a) Does the pulse have a definite

(i) frequency, (ii) wavelength, (iii) speed of propagation?

(b) If the pulse rate is 1 after every 20 s, (that is the whistle is blown for a split Of second after every 20s), is the frequency of the note

produced by the Whistle equal to 1/20 or 0.05 HL

24.

A wave is traveling along the x-axis, whose displacement- time graph is shown in Fig. Find the period and frequency of the wave.

25.

A source of wave produces 40 crests and 40 troughs in 0.4 seconds. Find the frequency of the wave.

26.

A boat at anchor is rocked by a wave whose consecutive crests are 100 m apart. the wave velocity of the moving crests is 20 m/s. what is the frequency of rocking of the boat?

27.

A Wave is produced on n toy slinky. The wave travels at a speed Of 30 cm/s and the frequency of the wave is 20 Hz. What is the minimum separation between the consecutive compressions of the slinky?

28.

what is the phase difference between the particles 1 and 2 located as shown in the figure?

29.

A wave of the frequency of 500 cycles/s has a phase velocity Of 360 m/s. (a) How far apart are two points 600 out of phase? (b) What is the phase difference between two displacements at a certain point at times ${10}^{-3}$s apart?

30.

$\mathrm{A}\mathrm{transverse}\mathrm{harmonic}\mathrm{wave}\mathrm{on}\mathrm{a}\mathrm{string}\mathrm{is}\mathrm{described}\mathrm{by}\mathrm{y}(\mathrm{x},\mathrm{t})=3.6\mathrm{sin}\left(36\mathrm{t}+0.018\mathrm{x}+3.0\mathrm{sin}\left(36\mathrm{t}+0.018\mathrm{x}+\frac{\mathrm{\pi}}{4}\right)\right),\phantom{\rule{0ex}{0ex}}\mathrm{where}\mathrm{x},\mathrm{y}\mathrm{are}\mathrm{in}\mathrm{cm}\mathrm{and}\mathrm{t}\mathrm{in}\mathrm{s}.\mathrm{The}\mathrm{positive}\mathrm{direction}\mathrm{of}\mathrm{x}\mathrm{is}\mathrm{from}\mathrm{left}\mathrm{to}\mathrm{right}.$

(i) Is this 2 traveling or a stationary wave? If it is traveling, what are tile speed and direction propagation?

(ii) What are its amplitude and frequency?

(iii) What is the Initial phase at the origin?

(iv) What Is distance between two successive crests in the wave?

31.

A tuning fork Of unknown frequency gives 4 beats with u tuning fork of frequency AZ. gives the Same number of bants on filing. Find the unknown frequency.

32.

A set of 56 tuning forks are arranged in? ±ries of increasing frequencies. Each fork gives. 4 beats/s with the preceding one. If the frequency of the last fork, is 2 times that of The first, what is the frequency of 40th fork?

33.

A bat is fitting about in cave, navigating in ultrasonic bleeps. Assume that the sound emission frequency of the bat is 40 kHz. During one fast sweep directly towards a flat wall surface, the bat is moving at 0.03 times the speed of sound in air. What frequency does the bat hear reflected off the wall?

34.

A source emitting sound at frequency 4000 Hz, is moving along the - axis with a speed of 22 m/s. A listener is situated on the ground at the position (660 m, 0). Find the frequency of the sound received by the listener at the instant the source crosses the origin. Speed of sound in air = 330 m/s.

35.

Now does the sound produced by a vibrating object in a medium reach your ear?

36.

Explain how sound is produced by your school bell.

37.

Why sound waves are called mechanical waves?

38.

Suppose you and your friend are on the moon. Will you be to hear any sound produced by your friend?

39.

Which does wave property determine (a) loudness, (b) pitch?

40.

Guess which sound has a higher pitch: guitar or car horn?

41.

What are the wavelength, frequency, time period and amplitude of a sound wave?

42.

How are the wavelength and frequency of a sound wave related to its speed?

43.

Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.

44.

A person io a tone of 500 Hz sitting at a distance of450 m from the source of the sound. What is the time interval between successive compressions from the source?

45.

Distinguish between loudness and intensity of sound.

46.

In which of three media: air, water or iron, does sound travel the fastest at a particular temperature?

47.

An echo returned in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is $342{\mathrm{ms}}^{-1}?$

48.

Why are the ceilings Of concerts halls curved ?

49.

what is the audible range of the average human ear?

50.

What is the range of frequencies associated with

(a) Infrasound

(b) Ultrasound

51.

A submarine emits a sonar pulse, which returns from an obstacle underwater cliff in 1.02s. If the speed of sound in saltwater is 1531 m/s, how far away is the cliff?

52.

What is sound and how is it produced?

53.

Describe with the help of a diagram, how compressions and are refractions are produced in the air near a source of the sound.

54.

Cite an experiment to show that sound needs a material medium for its propagation.

55.

Why is a sound wave called a longitudinal wave?

56.

Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a darkroom?

57.

Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?

58.

A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of the sound waves in air corresponding to these two frequencies? Take the speed of sound in air as $344{\mathrm{ms}}^{-1}.$

59.

Two children are opposite ends of an aluminum rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in the air and in aluminum to reach the second child.

60.

The frequency of a source/sound is 100 Hz. How many times does it vibrate in a minute?

61.

Does sound follow the same laws of reflection as light does? Explain.

62.

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?

63.

Give two practical applications of reflection of sound waves.

64.

A stone dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Giving, $\mathrm{g}=10{\mathrm{ms}}^{-1},$ and speed of sound $=340{\mathrm{ms}}^{-1}.$

65.

A sound wave travels at a speed of 339 ms-l. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?

66.

What is reverberation? How can it be reduced?

67.

What is the loudness of sound? What factors does it depend on?

68.

Explain how bats use ultrasound to catch prey.

69.

How is ultrasound used for cleaning?

70.

Explain the working and application of a sonar.

71.

A sonar device on a submarine sends out a signal and receives an echo 5 sec. later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.

72.

Explain how defects in a metal block can be detected using ultrasound.

73.

$\mathrm{The}\mathrm{given}\mathrm{graph}\left(\mathrm{Figure}\right)\mathrm{shows}\mathrm{the}\mathrm{displacement}\mathrm{versus}\mathrm{time}\mathrm{relation}\mathrm{for}\mathrm{a}\mathrm{disturbance}\mathrm{traveling}\mathrm{with}\mathrm{a}\mathrm{velocity}\mathrm{of}1500{\mathrm{ms}}^{-1}.\phantom{\rule{0ex}{0ex}}\mathrm{Calculate}\mathrm{the}\mathrm{wavelength}\mathrm{of}\mathrm{the}\mathrm{disturbance}.$

74.

A girl is sitting in the middle of a park of dimension 12 m x 12 m. On the left side of it there is a building adjoining {he park and on the right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.

75.

Why do we hear the sound produced by the humming bees while the sound of vibrations of pendulum is not heard?

76.

For hearing the loudest ticking sound heard by the ear, find the angle x in the figure.

77.

When a light or gound source moves toward you, is there an increase or a decrease in the wave speed?

78.

The echo of our sound is not heard in a small room, but it heard distinctly in a big hall. Explain it

79.

An observer notes that there is a 6-second interval between seeing a flash of lightning and hearing the clap thunder. How far away is the storm?

80.

Find the frequency of minimum distance between compression and rarefaction of a wire. If the length of the wire 1m and velocity of sound in air is 360 m/s.

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