# Physics Class 9 Sound Numericals

## Class 9 Sound Numericals

Here in this post, we will provide you with the best Physics Class 9 Sound Numericals with Solution. These Physics Class 9 Sound Numericals will help you make better concepts.

Note: Before looking for the solution, first try to solve it yourself, and when it becomes very difficult or if you want to check your solution, only then click the “answer and explanation’ box.

### Important Class 9 Sound Formula

Before you solve the Sound Numericals let us revise the important formula that will be used for solving the class 9 Sound Numericals. These are the basic sound formulas that will be used in the higher classes.

• velocity of sound wave = wavelength/time

Also, velocity = wavelength × frequency

• frequency = 1/time period

Also, frequency = no. of vibrations/time-taken

• To solve Echo Problems, Use

2×distance = speed×time

• Frequency of Audible Range- 20 Hz to 20000 Hz

### Class 9 Sound Numericals with Solution

Q1. Find the frequency of a wave if a sound source produces 40 crests and 40 troughs in 0.5 seconds.

Q2. Will a wave be audible if it has a wavelength of 0.6 cm and travels at a speed of 332 m/s?

Q3. How much distance a sound of frequency 620 Hz produced by a tuning fork will travel in the air if it makes 45 vibrations? (Speed of Sound in Air= 336 m/s).

Q4. What is the distance of the reflecting surface from the source if an echo is returned in 3s? (Take the Speed of Sound in air 342 m/s).

Q5. What is the frequency of a wave if its time period is 0.04s?

Watch this Video for an explanation

Timeline-

Q1- 0:27

Q2- 2:33

Q3- 5:02

Q4- 8:37

Q5- 10:41

Q6. A radio broadcast at 30 m. Find the frequency of the station.

Q7. If a solar pulse emitted by a submarine returns from an underwater cliff in 1.5 seconds then find the distance of the cliff from the submarine. (Take the speed of sound in water- 1531 m/s).

Q8. A sound wave travels through the air with a frequency of 440 Hz. Calculate the wavelength of this sound wave if the speed of sound in air is 343 meters per second.

λ = speed of sound/frequency

Speed of Sound in the air (v) = 343 m/s [Given]

Frequency of the sound wave (f) = 440 Hz [Given]

Substituting these values in the above formula:

λ = 343/440 = 0.7795 meters

Q9. A tuning fork vibrates at a frequency of 256 Hz. Calculate the wavelength of the sound it produces when it travels through water. The speed of sound in water is approximately 1,480 meters per second.

Solve as above in Q8

Q10. A sound has a frequency of 600 Hz and travels at a speed of 330 m/s. Find the wavelength of the sound.

Q11. If 41 waves are produced in one second, then what will be the frequency?

Q12. If a body vibrates with a time period of 6 milliseconds and travels with a velocity of 1350 m/s. Find its wavelength.

Q13. A man is at the top of a building at a height of 75 m. His keys falls and he hears the sound of the keys hitting the ground after 5 seconds. Find the speed of the sound?

Q15. A child watching Dusshera celebrations from a distance sees the effigy of Ravana burst into flames and hears the explosion after 2 seconds. How far was he from the effigy? (Take speed of sound 344 m/s).

### Class 9 sound Numericals NCERT

Note: The data of some of the questions are changed.

Q1. A sound wave has a frequency of 1.4 kHz and a wavelength of 35 cm. How long will it take to travel 2.5 km?

Q2. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.

Q3. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?

Q4. An echo is heard in 3 seconds. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m/s?

Q5. .2 A person clapped his hands near a cliff and heard the echo after 2 s. What is the distance of the cliff from the person if the speed of the sound, v is taken as 346 m/s?

Q6. A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 m/s.

Q7. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

Q8. 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 m s–2 and speed of sound = 340 m/s.

Q9. A sound wave travels at a speed of 339 m/s. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?