Physics 20 Sound Unit Exam
Is this you?
Formulas:
Speed of sound:
v  f
v
d
t
v  332  0.63T
String Vibrations:
f1
L
 2
f2
L1
The Doppler Effect:
 v 

f 2  f1
 v  vs 
f1 d 2

f 2 d1
f1

f2
T1
T2
f1

f2
Beat Frequency:
beat frequency = f 2  f 1
1. Calculate the speed of sound at the following temperatures. (3 marks)
a) 0°C
b) 32°C
c) -18°C
2. If the speed of sound in air is 360m/s what is the temperature? (2 marks)
3. What is the Mach number of a plane flying at 10 000 km/h? (2 marks)
D2
D1
4. Which three small bones in the middle ear amplify vibrations, allowing you to hear? (3
marks)
5. Define mechanical resonance and explain how a sound can cause glass to shatter. (2 marks)
6. Lexie hears the sound of a firing cannon 60.0 s after seeing the flash on a 25.0°C day.
Assuming she sees the flash instantaneously, how far is she from the cannon? (3 marks)
7. Karrie claps her hands and hears the echo from a distant wall 0.20s later. How far is she from
the wall, if the temperature is -22.0°C? (3 marks)
8. A camera determines the distance to the subject by sending out a sound wave and measuring
the time needed for the echo to return to the camera. How long would it take the sound wave to
return to the camera if the subject were 3.00 m away on a 32.0°C day? (3 marks)
9. If the wavelength of a 440. Hz sound wave in water is 3.30m, what is the speed of sound in
water? (3 marks)
10. The frequency of a guitar string is 495 Hz when it is 60.5cm long. What is the frequency
when the same string is held, shortening its length to 45.0cm? (3 marks)
11. Explain the Doppler Effect. Include a sketch to aid your answer. (4 marks)
12. A car traveling at 115km/h blares its horn, which has a frequency of 450Hz. What is the
frequency of the pitch as the car is approaching you? (3 marks)
13. Explain how a radar gun, used by police to catch speeders, works. (3 marks)
14. Sketch the following situations: (3 marks)
a) Sound waves being emitted by a stationary object.
b)Sound waves being emitted by an object moving subsonically.
c) Sound waves being emitted by an object moving supersonically.