Physics Solutions Manual

Chapter 15 continued
87. A bird on a newly discovered planet flies
toward a surprised astronaut at a speed of
19.5 m/s while singing at a pitch of 945 Hz.
The astronaut hears a tone of 985 Hz. What
is the speed of sound in the atmosphere of
this planet?
f d 985 Hz, f s 945 Hz, v s 19.5 m/s,
v ?
fd
v 1
fs
v vs 1 vs
v
So vs
fs
1 ,
v fd
19.5 m/s
or v
1 9 vs
fs
45
Hz
1 f
985
Hz
d
4.8010 2 m/s
88. In North America, one of the hottest outdoor
temperatures ever recorded is 57°C
and one of the coldest is 62°C. What are
the speeds of sound at those two temperatures?
v(T) v(0°C) (0.6 m/s)T, where
v(0°C) 331 m/s. So, v(57°C)
(331 m/s) 0.6 m/s
(57°C)
°C
365 m/s
v(62°C) (331 m/s) 0.6 m/s
(62°C)
°C
294 m/s
Level 2
89. A ship’s sonar uses a frequency of 22.5 kHz.
The speed of sound in seawater is 1533 m/s.
What is the frequency received on the ship
that was reflected from a whale traveling at
4.15 m/s away from the ship? Assume that
the ship is at rest.
Part 1. From ship to whale:
v d 4.15 m/s, v 1533 m/s,
fs 22.5 kHz, vs 0
fd fsv vd
(22.5 kHz)
v v
1533
4.15
1533
s
22.4 kHz
Part 2. From whale to ship:
v s 4.15 m/s, v 1533 m/s,
fs 22.4 kHz, vd 0
fd fsv vd
(22.4 kHz) v v
1533
1533 4.15
s
22.3 kHz
90. When a wet finger is rubbed around the rim
of a glass, a loud tone of frequency 2100 Hz
is produced. If the glass has a diameter of
6.2 cm and the vibration contains one
wavelength around its rim, what is the
speed of the wave in the glass?
The wavelength is equal to the
circumference of the glass rim, d
Therefore, the speed is
v f df
(0.062 m)(2100 Hz) 4.110 2 m/s
91. History of Science In 1845, Dutch scientist
Christoph Buys-Ballot developed a test
of the Doppler effect. He had a trumpet
player sound an A note at 440 Hz while
riding on a flatcar pulled by a locomotive.
At the same time, a stationary trumpeter
played the same note. Buys-Ballot heard
3.0 beats per second. How fast was the train
moving toward him?
f d 440 Hz 3.0 Hz 443 Hz
d
s
fd fsv v
v v
so (v v s )f d (v v d )f s and
(v vd )fs vs v
fd 343 m/s
2.3 m/s
92. You try to repeat Buys-Ballot’s experiment
from the previous problem. You plan to
have a trumpet played in a rapidly moving
car. Rather than listening for beat notes,
however, you want to have the car move fast
enough so that the moving trumpet sounds
one major third above a stationary trumpet.
a. How fast would the car have to move?
major third ratio 5
4
(343 m/s 0)(440 Hz)
443 Hz
340 Solutions Manual Physics: Principles and Problems
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.