Chapter 14 solved problems
29.
Picture the Problem:
We need to calculate the wavelength of sound in air from its frequency.
Strategy:
Solve equation 141 for the wavelength, using 343 m/s for the speed of sound in air.
Solution:
1. (a)
Solve equation 141 for the
wavelength:
343 m/s
0.807 m
425 Hz
v
f
λ
=
=
=
2.
(b)
Examine the relationship between
wavelength and frequency:
Wavelength is inversely related to frequency so, if the
frequency increases the wavelength decreases.
3. (c)
Calculate the wavelength at 450 Hz:
343 m/s
0.722 m
475 Hz
λ
=
=
Insight:
As predicted, an increase in frequency corresponds to a decrease in wavelength.
48.
Picture the Problem
: The image shows a
motorcyclist and police car approaching each other.
Strategy:
We want to calculate the frequency at
which the motorcyclist hears the police car’s siren.
In
this problem both the source (police car) and the
observer (motorcycle) are moving toward each other.
Use equation 1411, with the plus sign in the
numerator and the minus sign in the denominator, to
calculate the observed frequency.
Solution:
Insert the speeds and
emitted frequency into equation
1411:
(
29
(
29
(
29
o
1
1
1
13.0 m/s
343 m/s
512 Hz
577 Hz
1
27.0 m/s
343 m/s
s
u
v
f
f
u
v
+
′ =
÷

+
=
=

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 Spring '11
 BEAN
 pH, Frequency, Wavelength, police car

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