Unformatted text preview: The Physics of Light & Sound
PRACTICE PROBLEMS
GENERAL SCIENCE 121 SUMMER 2011 1. A pendulum on the Earth’s surface has a bob of length 0.2 m. What is the natural frequency in Hz
Sean T
11
of this system? ANSWER: 1.11 Scully  GSCI121_3_4_SP10
Hz
Homework #4
2. What length of pendulum is required to produce a period of 2 seconds? ANSWER: 1 m
4 Due date: Wed Feb
23:00:00 2010
3. What is the amplitude of the wave below:24 ANSWER: 1.5 m. 3 4
2 position (m) 3 Position (m) 2
1 1
0
−1 0
−2
−1
−3
−2
−4
0 −3 4 6 8 10 time (s) What −4
−4 What 2 is the −2 amplitude 0
Time (s) of 4. What is its period? ANSWER 6 seconds
Tries 0/10
Answer • 1.5 for Part:
5. What is its frequency? ANSWER: 0.17[1.425
Hz
0
1.575] this 2 is the period of this wave (in seconds)? 4 Tries 0/10 wave (in meters)? Answer
for Part:
0 • 6.0
[5.7
6.3] Water waves are observed to pass under a bridge at a rate of
one complete wave every 3 s. What is the frequency (in hz)
of these waves? 6. If this is a sound wave with c = Two instruments play a note is the same time. One produces ANSWER: 1986 m
331 m/s, what at its wavelength? Tries 0/10
a wave that has a frequency of 236 Hz and the other produces
Answer
• 0.333333333333333
a wave of 228 Hz. What is the frequency of the resulting beats
for Part:
7. Two instruments play a note at(inthe same time. One produces a wave that has a frequency of 236
[0.316666666666666
Hz)?
0
0.35]
Tries 0/10 of 228 Hz. What is the frequency of the0 resulting beats (in
Hz and the other produces a wave
Sig
 15
Answer
•8
A vibrating tuning fork produces waves with a waveHz)? ANSWER: 8 Hz
for Part:
[7.6
length of 9 m and a frequency of 10 Hz. How fast do
0
8.4]
these waves travel away from the tuning fork (in m/s)?
8. What frequency does your ear hear? ANSWER: 232 Hz
Sig 0  15
Tries 0/10
9. Water waves are observed to pass under a bridge at a rate of oneAnswer
complete wave every 3 s. What
• 90
is the frequency (in Hz) of these waves? ANSWER: 0.33 Hz for Part:
[85.5
0
94.5]
Sig 0  15
10. A vibrating tuning fork produces waves with a wavelength of 9 m and a frequency of 10 Hz. How
fast do these waves travel away from the tuning fork (in m/s)? ANSWER: 90 m/s
11. You are in the Grand Canyon. You yell out "HELLO!" 4 seconds later you hear your echo. How far
away is the canyon wall (in meters) if the speed of sound through air is approximately 340 m/s?
ANSWER: 680 m
12. A wave is observed to have a period of 8 seconds. What is the frequency of this wave (in Hz)?
ANSWER: 0.125 Hz
13. A transverse wave is transporting energy from east to west. The particles of the medium will
move:
A) easterly
B) Both northward and southward
C) Both eastward and westward
D) northerly Summer 2011 1 Practice Problems 14. A wave has a frequency of 256 Hz and a wavelength of λ = 1.1 m. What is the wave speed (in m/
s)? ANSWER: 282 m/s
15. A horn is known to emit a sound of 356 Hz when stationary. If the speed of sound is 340 m/s,
how fast (away or towards) is the horn moving if the frequency heard is measured to be 400 Hz?
ANSWER: 42 m/s towards the observer
16. A trumpet produces a pitch of 440 Hz. The trumpet is now set in motion away from the listener
at a speed of 30 m/s. If the speed of sound is 340 m/s, what frequency would be heard by a
stationary observer? ANSWER: 401 Hz
17. The temperature in Harrisonburg is 10 C. What is the speed of sound through air (in m/s)?
ANSWER: 331.6 m/s
18. Which of the following are units of sound intensity?
A) dB (decibels)
B) kg m/s/s
C) W/m (Watts per meter)
D) W (Watts)
19. With one violin playing the sound level at a certain place is measured to be 50 dB. If instead 10
violins are play ing equally as loudly, what will be the sound level (dB)? ANSWER: 60 dB
20. The background noise in a room is measured to be 63 dB. How many dB is 1000 times louder?
ANSWER: 93 dB
21. A sound source produces a sound measured to be 66 dB at some distance. Suppose now I am
twice as far away. What will my sound meter register? ANSWER: 63 dB
22. A triangle makes a sound of intensity 82 dB. How loud are two triangles? ANSWER: 85 dB
23. The part of the ear responsible for converting mechanical pressure into nerve impulses is:
A) The Pinna
B) The Stapes
C) The Cochlea
D) The Ear Drum
24. What is the log of 12589? ANSWER: 4.1
25. The human ear can hear frequencies from 20 hz up to 20,000 hz. What is the wavelength (in m)
of the highest frequency a human can hear in air if the temperature is 10 C? ANSWER: 0.017
m Summer 2011 2 Practice Problems ...
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