SOLUTIONS – MONDAY, DECEMBER 10
16.13.
IDENTIFY:
For transverse waves,
trans
.
F
v
μ
=
For longitudinal waves,
long
.
Y
v
ρ
=
SET UP:
The mass per unit length
is related to the density (assumed uniform) and the crosssection area
A
by
.
μ
A
ρ
=
EXECUTE:
gives
long
trans
30
vv
=
30
YF
ρμ
=
and
900
.
Υ
F
ρ
Αρ
=
Therefore,
.
900
Υ
FA
=
EVALUATE:
Typical values of
Y
are on the order of
so the stress must be about
If
A
is on the
order of
this requires a force of about 100 N.
11
10 Pa,
8
10 Pa.
26
1 mm
10 m ,
−
=
2
16.20.
IDENTIFY
and
SET UP:
Apply the relation
that is derived in Example 16.10.
21
2
1
(10 dB) log (
/
)
II
ββ
−=
EXECUTE:
(a)
( )
4
(10 dB)log
6.0 dB
I
I
β
Δ=
=
(b)
The total number of crying babies must be multiplied by four, for an increase of 12 kids.
EVALUATE:
For
2
,
1
α
=
where
is some factor, the increase in sound intensity level is
(10 dB)log .
For
4,
=
6.0 dB.
16.34.
IDENTIFY:
Constructive interference occurs when the difference of the distances of each source from point
P
is
an integer number of wavelengths. The interference is destructive when this difference of path lengths is a half
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 Fall '07
 Evrard
 Mass, Wavelength

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