johnson (mjj622) – HW 16 – Coker – (56625)
1
This printout should have 16 questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
This assignment covers the material dis
cussing sound waves as presented in class,
including longitudinal pressure waves, sound
intensity, loudness, the Doppler e±ect, and
standing sound waves.
001
10.0 points
Sound with a Frequency oF 430 Hz travels
through steel. A wavelength oF 14
.
46 m is
measured.
What is the speed oF the sound in steel?
Correct answer: 6217
.
8 m
/
s.
Explanation:
Let :
f
= 430 Hz
and
λ
= 14
.
46 m
.
v
=
f λ
= (430 Hz) (14
.
46 m)
=
6217
.
8 m
/
s
.
002
10.0 points
Calculate the pressure
amplitude oF a
1
.
36 kHz sound wave in air iF the displace
ment amplitude is 2
.
35
×
10
−
8
m. Take the
velocity oF sound in air to be 343 m
/
s and the
density oF air to be 1
.
31 kg
/
m
3
.
Correct answer: 0
.
0902302 Pa.
Explanation:
Let :
f
= 1
.
36 kHz = 1360 Hz
,
A
= 2
.
35
×
10
−
8
m
,
v
s
= 343 m
/
s
,
and
ρ
= 1
.
31 kg
/
m
3
.
The pressure amplitude is
Δ
P
=
ρ ω v
s
A
=
ρ
(2
π f
)
v
s
A
= (1
.
31 kg
/
m
3
) 2
π
(1360 Hz)
×
(343 m
/
s) (2
.
35
×
10
−
8
m)
=
0
.
0902302 Pa
.
003 (part 1 of 2) 10.0 points
A sinusoidal sound wave in a gas oF density
1
.
3 kg
3
/
m has molecular displacement
s
(
x, t
) =
s
m
cos(
k x
−
ω t
)
,
where
s
m
= 4
μ
m,
k
= 728 m
−
1
, and
ω
= 4
.
4408
×
10
5
s
−
1
.
What is the speed oF this wave?
Correct answer: 610 m
/
s.
Explanation:
Let :
k
= 728 m
−
1
and
ω
= 4
.
4408
×
10
5
s
−
1
.
The speed oF the wave is
v
=
ω
k
=
4
.
4408
×
10
5
s
−
1
728 m
−
1
=
610 m
/
s
.
004 (part 2 of 2) 10.0 points
What is the intensity oF this wave?
Correct answer: 1251
.
08 W
/
m
2
.
Explanation:
Let :
ρ
= 1
.
3 kg
3
/
m
and
s
m
= 4
μ
m = 4
×
10
−
6
m
.
I
=
1
2
ρ v
(
ω s
m
)
2
=
1
2
(1
.
3 kg
3
/
m) (610 m
/
s)
×
(4
.
4408
×
10
5
s
−
1
)
2
×
(4
×
10
−
6
m)
2
=
1251
.
08 W
/
m
2
.
005 (part 1 of 2) 10.0 points
The area oF a typical eardrum is about
4
.
9
×
10
−
5
m
2
.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Documentjohnson (mjj622) – HW 16 – Coker – (56625)
2
Find the sound power (the energy per sec
ond) incident on an eardrum at the threshold
of hearing
(
1
×
10
−
12
W
/
m
2
)
.
Correct answer: 4
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '08
 Turner
 Correct Answer, Coker

Click to edit the document details