Questions and answers calculatios sound

• speed calculations
• Voortgezet speciaal onderwijs
• Leerroute 2

Questions

• You are in a breakout room as a group of four.
  

• one of you shares their screen with this lesson up on it.
  

• You are going to do questions, one of you writes down your answers in a word document.
  

Two formulas to calculate the speed of sound

speed=​time​​distance​​

speedofsound=wavelength⋅frequency

speed=​time​​distance​​

v=​t​​d​​

• v: speed in m/s
  
• d: distance in m
  
• t: time in s
  

3=​2​​6​​

• v_s: the speed of sound (m/s)
  
• λ: wavelength (m)
• f: frequency (Hz)
  

speedofsound=wavelength⋅frequency

v_s = λ • f

6=2⋅3

David drives 150 km in 2 hours. Calculate his average speed in km/h. Show your calculations.

Fatima runs 200 meters in 40 seconds. Calculate her average speed in m/s. Show your calculations.

There is a thunderstorm on its way. You see lightning. It takes 4 seconds before you hear the thunder. The speed of sound through air is 343 m/s. How far is the thunderstorm away?

 Someone makes a yell in a mountain valley. The closest mountain is at a distance of 411,6 meters away from them. The speed of sound in air is 343 m/s.  How long will it take before they hear the echo?

1. 4,8 seconds
2. 3 seconds
3. 5 seconds
4. 2,4 seconds

Given:

• v = 343 m/s
• d = 411,6 m x 2 = 823,2 m

Asked:

• How long will it take before they hear the echo?

Formula:

•  v = d/t     —>       t = d/v

Calculation:

•  t = 823,2 / 343 = 2,4 s

 Someone makes a yell in a mountain valley. The closest mountain is at a distance of 411,6 meters away from them. The speed of sound in air is 343 m/s. How long will it take before they hear the echo?

A sound wave traveling through copper has a frequency of 400Hz. It has a wavelength of 5,65m. 

Calculate the speed of sound in copper.

1. 70.8 m/s
2. 600 m/s
3. 2260 m/s
4. 2460 m/s

Given:

• Frequency = 400 Hz
• Wavelength = 5.65 m

Asked:

• Calculate the speed of sound in copper

Formula:

•  Speed of sound = wavelength • frequency

Calculation:

•  Speed of sound = 400 x 5,65 = 2260 m/s

A sound wave traveling through copper has a frequency of 400 Hz. It has a wavelength of 5,65 m. Calculate the speed of sound in copper.

Explain why sound moves faster through a solid in compare to a gas?

Questions 1

a) Write down the two formulas to calculate the speed of sound.

v= d /t       —        vs = λ • f        

b) For each formula, write it out how to transform it for each variable.

v= d  /t          —       d= v • t       —          t= d / v

vs = λ • f        —     λ= vs / f       —          f = vs / λ         

Questions 2

 Explain why doing the wavelength of a wave times the frequency of that wave results in the speed of that wave.

The frequency gives you the amount of waves per second. 

The wavelength gives you the length of each wave in meters.

Multiplying the amount of waves per second times the length of each wave gives you the distance a sound wave travels in one second.

Questions 3

The speed of sound is 343 m/s in air at room temperature.

a) calculate the wavelength of a sound wave with a frequency of 20000 Hz.

λ = vs / f

vs = 343 m/s

f = 20000 Hz

λ = 343 / 20000 = 0.01715 m

b) calculate the frequency of a sound wave with a frequency of 20 Hz.

λ = vs / f

vs = 343 m/s

f = 20 Hz

λ = 343 / 20 = 17.15 m

Questions 4

a) A lighting flash strikes 4459 meters away from someone. 13 seconds later, the thunder is heard. Prove that the speed of sound is 343 m/s. 

v= d /t

d = 4459 m

t = 13 s

v = 4459/13 = 343 m/s

b) If the wavelength of the thunder is 4,9 m, what would its frequency be?

 f = vs / λ

vs = 343 m/s

λ = 4.9 m

 f = 343 /4.9 = 70 Hz

Questions 5

A submarines sonar measures an echo 0.1 second after sending out a sound wave. The speed of sound through water is 1480 m/s. how close is the object the submarine detected?

 v = d / t        —>        d =v • t

v = 1480 m/s

t = 0.1          —>      0.1/2= 0.05.

d = 1480 • 0.05 = 74 m

 (you have to take into account that in echo sound has to travel there and back)

Questions 6

Calculate the frequency of a sound wave traveling through air with a wavelength of 0.6 m.

Note: the speed of sound in air is 343 m/s

f = vs / λ  

vs = 343 m/s

λ = 0.6 m

f = 343 • 0.6 = 205.8 Hz