1. Does the period of a pendulum depend on the mass
of the bob? On the length of the string?
2. A heavy person and a light person swing to and fro on
swings of the same length. Who has the longer period?
3. A grandfather pendulum clock keeps perfect time.
Then it is brought to a summer home high in the
mountains. Does it run faster, slower, or the same?
Explain.
4. If a pendulum is shortened, does its frequency
increase or decrease? What about its period?
5. You pick up an empty suitcase and let it swing to and
fro at its natural frequency. If the case were filled
with books, would the natural frequency be lower,
greater, or the same as before?
6. Is the time required to swing to and fro (the period)
on a playground swing longer or shorter when you
stand rather than sit? Explain.
7. Why does it make sense that the mass of a bob in a
simple pendulum doesn't affect the frequency of the
pendulum?
8. What happens to the period of a wave when the
frequency decreases?
9. What happens to the wavelength of a wave when the
frequency decreases?
10. If the speed of a wave doubles while the frequency
remains the same, what happens to the wavelength?
11. If the speed of a wave doubles while the wavelength
remains the same, what happens to the frequency?
12. If you clamp one end of a hacksaw blade in a vice
and twang the free end, it vibrates. Now repeat, but
first place a wad of clay on the free end. How, if at
all, will the frequency ofvibration differ? Would it
make a difference if the wad of clay were stuck to the
middle? Explain. (Why could this question have been
asked back in Chapter 8?)
13. The needle of a sewing machine moves up and down
in simple harmonic motion. Its driving force comes
from a rotating wheel that is powered by an electric
motor. How do you suppose the period of the upand-
down needle compares with the period of the
rotating wheel?
14. If you shake the end of a spring to produce a wave,
how does the frequency of the wave compare with
the frequency of your shaking hand? Does your
answer depend on whether you're producing a
transverse wave or a longitudinal wave? Defend
your answer.
15. What kind of motion should you impart to the nozzle
of a garden hose so that the resulting stream ofwater
approximates a sine curve?
16. What kind of motion should you impart to a
stretched coiled spring (or Slinky) to provide a
transverse wave? To provide a longitudinal wave?
17. What kind of wave is each of the following? (a) An
ocean wave rolling toward Waikiki Beach. (b) The
sound of one whale calling another whale under
water. (c) A pulse sent down a stretched rope by
snapping one end of it.
18. If a gas tap is turned on for a few seconds, someone
a couple of meters away will hear the gas escaping
long before she smells it. What does this indicate
about the speed of sound and the motion of
molecules in the sound-carrying medium?
19. If we double the frequency of a vibrating object
or the wave it produces, what happens to the
period?
20. Do the two terms wave speed and wave frequency refer
to the same thing? Defend your answer.
21. Red light has a longer wavelength than violet light.
Which has the greater frequency?
22. Consider a wave traveling along a thick rope tied to a
thin rope. Which ofthese three wave characteristics
does not undergo change-speed, frequency, or
wavelength?
23. What is the frequency of the second hand of a clock?
The minute hand? The hour hand?
24. What is the source of wave motion?
25. If you dip your finger repeatedly into a puddle of
water, it creates waves. What happens to the
wavelength if you dip your finger more frequently?
26. How does the frequency of vibration of a small
object floating in water compare with the number of
waves passing it each second?
27. How far, in terms of wavelength, does a wave travel
in one period?
28. How many nodes, not including the end points, are
there in a standing wave that is two wavelengths
long? Three wavelengths long?
29. A rock is dropped in water, and waves spread over
the flat surface of the water. What becomes of the
energy in these waves when they die out?
30. The wave patterns seen in Figure 19.6 are composed
of circles. What does this tell you about the speed of
waves moving in different directions?
31. Why is lightning seen before thunder is heard?
32. A banjo player plucks the middle of an open string.
Where are the nodes of the standing wave in the
string? What is the wavelength ofthe vibrating string?
33. Violinists sometimes bow a string to produce
maximum vibration (antinodes) at one-quarter
and three-quarters of the string length rather than at
the middle ofthe string. Then the string vibrates with
a wavelength equal to the string length rather than
twice the string length. (See Figures 19.14a and b).
What is the effect on frequency when this occurs?
34. A bat chirps as it flies toward a wall. Is the frequency
of the echoed chirps it receives higher, lower, or the
same as the emitted ones?
35. Why is there a Doppler effect when the source of
sound is stationary and the listener is in motion? In
which direction should the listener move to hear a
higher frequency? A lower frequency?
36. A railroad locomotive is at rest with its whistle shrieking,
then starts moving toward you. (a) Does the
frequency that you hear increase, decrease, or stay
the same? (b) How about the wavelength reaching
your ear? (c) How about the speed of sound in the
air between you and the locomotive?
37. When you blow your horn while driving toward a
stationary listener, the listener hears an increase in
frequency of the horn. Would the listener hear an
increase in horn frequency if he or she were also in a
car traveling at the same speed in the same direction
as you are? Explain.
38. Is there an appreciable Doppler effect when the
motion of the source is at right angles to a listener?
Explain.
39. How does the Doppler effect aid police in detecting
speeding motorists?
40. Astronomers find that light emitted by a particular
element at one edge of the Sun has a slightly higher
frequency than light from that element at the
opposite edge. What do these measurements tell us
about the Sun's motion?
41. Would it be correct to say that the Doppler effect is
the apparent change in the speed of a wave due to
motion of the source? (Why is this question a test of
reading comprehension as well as a test of physics
knowledge?)
42. How does the phenomenon of interference play a
role in rhe production of bow waves or shock
waves?
43. What can you say about the speed of a boat that
makes a bow wave?
44. Does the conical angle of a shock wave open wider,
narrow down, or remain constant as a supersonic
aircraft increases its speed?
45. Ifthe sound of an airplane does not come from the
part of the sky where the plane is seen, does this
imply that the airplane is traveling faster than the
speed of sound? Explain.
46. Does a sonic boom occur at the moment when an
aircraft exceeds the speed of sound? Explain.
47. Why is it that a subsonic aircraft, no matter how
loud it may be, cannot produce a sonic boom?
48. Imagine a superfast fish that is able to swim faster
than the speed of sound in water. Would such a fish
produce a "sonic boom"?
49. Make up a multiple-choice question that would
check a classmate's understanding of the distinction
between a transverse wave and a longitudinal wave.
50. Make up two multiple-choice questions that would
check a classmate's understanding of the terms that
describe a wave.
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