Question:
A stone is 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 ? Given,g = 10 and speed of sound = 340 m/s.
Answer:
Here,height through which the stone falls,h = 500 m
speed of sound,v = 340 m/s,g=10
If t is the time taken by the stone to fall through h,then
h = Or t = =Or t = =10 s
Further, if t'is the time taken by sound (produced as a result splashing) to travel to the top of the tower,
t = = =1.47 s
Time after which the splash is heard at the top of the tower=t + t'=10 s + 1.47 s
=11.47 s
Sound
Q 1.
What are the factors speed of sound wave depends upon?
Q 2.
What is a wave number?
Q 3.
What are ultrasonics?
Q 4.
The sound of distant horses can be heard by applying the ear to the ground whereas it is inaudible if the ear is held a little distance above the ground.Explain.
Q 5.
How are compressions and rarefactions produced near a source of sound ?
Q 6.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 7.
What type of waves can travel in vacuum? Give example(s).
Q 8.
How is sound propagated through a material medium ? What is wave motion ?
Q 9.
Sounds we hear inform us of the state of world around us,especially of that part of it which our other senses,such as touch and sight,cannot reach.Illustrate this with appropriate examples.
Q 10.
Fill in the blanks :
v = ? × ?
Q 11.
What propagates along with the waves ?
Q 12.
Fill in the blanks :
Waves transport _________ not matter.
Q 13.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 14.
How are the wavelength and frequency of a sound wave related to its speed?
Q 15.
What is infrasonic? Give an example.
Q 16.
A person standing between two vertical cliffs and 680 m away from the nearest cliff,shouted.He heard the first echo after 4 s and the second echo 3 s later.Calculate (a) the speed of sound in air and (b) distance between the two cliffs.
Q 17.
Explain how sound is produced by your school bell ?
Q 18.
What is audible range ?
Q 19.
Why do we use upholstered seats in theatres and halls ?
Q 20.
A hospital uses an ultrasonic scanner to locate tumors in a tissue. What is the wavelength of sound in a tissue is which the speed of sound is 1.7 km/s. The operating frequency of the scanner is 4.2 MHz. (1MHz = 10
6 Hz).
Q 21.
A stone is 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 ? Given,g = 10
and speed of sound = 340 m/s.
Q 23.
Hearing may be damaged by excessive noise.So our ears sometimes need protection from continuous loud sound. Hearing damage depends on the sound intensity level (decibel level)and the exposure time,and the exact combinations vary for different people.Normally,at 90 dB,it takes 8 hours or less for the damage to receptor nerves to occur.Further,it is found that if the sound level is increased by 5 dB,the safe exposure limit is cut to half.
(a) How long will it take for a sound of a very loud lawn mower (or a motorcycle) of 95dB to damage the hearing ?
(b) What is the nonstop exposure time for a 105 dB sound to damage the ear ?
(c) What should be done to protect the society from the danger of losing the divine gift of hearing power ?
Q 24.
Fill in the blanks :
In a __________ wave the particles of the medium oscillate in a direction perpendicular to the direction in which the wave propagates.
Q 25.
Fill in the blanks :
If the time interval between original sound and reflected sound is more than 1/10 second then original sound and reflected sound can be heard clearly. This reflected sound is known as _______.
Q 26.
What is speed of sound in air?
Q 27.
Three persons, A, B and C are made to hear a sound travelling through different mediums as given below:
| Persons | Medium |
| A | Iron Rod |
| B | Air |
| C | Water |
Who will hear the sound first? Why?
Q 28.
A sound wave travels at a speed of 339 ms
–1. If its wavelength is 1.5 cm, what is the frequency of the wave?
Q 29.
What type of wave is represented by density- distance graph?
Q 30.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 31.
Explain the working and application of a sonar.
Q 32.
Deaf people can be made to dance to music.Explain how ?
Q 33.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 34.
What is a mechanical wave?
Q 35.
What are wavelength, frequency, time period and amplitude of a sound wave?
Q 36.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 37.
Give an application use of ultrasonics.
Q 38.
Guess which sound has a higher pitch: guitar or car horn?
Q 39.
sonar emits pulses on the surface of water which are detected after reflection from its bottom at a depth 1531 m.If the time interval between the emission and detection of the pulse is 2 s,find the speed of : sound in water.
Q 40.
What is the audible range of the average human ear ?
Q 42.
How can you show that sound waves are longitudinal waves ?
Q 43.
Fill in the blanks :
A ________ (pulse/wave) is a disturbance which is sudden and lasts for a short duration of time.
Q 44.
What is reverberation?
Q 45.
Which wave characteristics determine the
(a) Loudness (b) pitch of sound?
Draw two different waveforms and mark these characteristics on it.
Q 46.
A man standing at 51 m from a wall fires a gun.Calculate the time after which an echo is heard.The speed of sound is 340 m/s.
Q 47.
A ship sends out ultrasound that returns from the seabed and is detected after 3.42 s.If the speed of the ultrasound through sea water is 1531 m/s,what is the distance of the seabed from the ship ?
Q 48.
What is the difference between an echo and a reverberation ?
Q 49.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 50.
What is sonic boom and when is it heard ?
