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24. Does the Doppler effect occur when the observer is moving and 35. The fundamental frequency of a standing wave on a string has
the source of sound is stationary? a. one node and one antinode.
a. Yes, the effect is the same. b. one node and two antinodes.
b. No, the source must be moving. c. two nodes and one antinode.
c. Yes, but the change of pitch effects is reversed in this case. d. two nodes and two antinodes.
25. A rocket traveling at three times the speed of sound is traveling at 36. An observer on the ground will hear a sonic boom from an
a. sonic speed. airplane traveling faster than the speed of sound
b. Mach speed. a. only when the plane breaks the sound barrier.
c. Mach 3. b. as the plane is approaching.
d. subsonic speed. c. when the plane is directly overhead.
26. A longitudinal mechanical wave causes particles of a material d. after the plane has passed by.
to move 37. What comment is true about the statement that “the human ear
a. back and forth in the same direction the wave is moving. hears sounds originating from vibrating objects with a frequency
b. perpendicular to the direction the wave is moving. between 20 and 20,000 Hz”?
c. in a circular motion in the direction the wave is moving. a. This is true only at room temperature.
d. in a circular motion opposite the direction the wave is moving. b. About 95 percent hear in this range, while some hear outside
27. A transverse mechanical wave causes particles of a material to move the average limits.
a. back and forth in the same direction the wave is moving. c. This varies, with females hearing frequencies above 20,000 Hz.
b. perpendicular to the direction the wave is moving. d. Very few people hear this whole range, which decreases
c. in a circular motion in the direction the wave is moving. with age.
d. in a circular motion opposite the direction the wave is moving. 38. A sound wave that moves through the air is
28. Transverse mechanical waves will move only through a. actually a tiny sound that the ear magnifies.
a. solids. b. pulses of increased and decreased air pressure.
b. liquids. c. a transverse wave that carries information about a sound.
c. gases. d. a combination of longitudinal and transverse wave
d. All of the above are correct. patterns.
29. Longitudinal mechanical waves will move only through 39. During a track and field meet, the time difference between
a. solids. seeing the smoke from a starter’s gun and hearing the bang
b. liquids. would be less
c. gases. a. on a warmer day.
d. All of the above are correct. b. on a cooler day.
30. A pulse of jammed-together molecules that quickly moves away c. if a more powerful shell were used.
from a vibrating object d. if a less powerful shell were used.
a. is called a condensation. 40. What is changed by destructive interference of a sound
b. causes an increased air pressure when it reaches an object. wave?
c. has a greater density than the surrounding air. a. Frequency
d. All of the above are correct. b. Phase
31. The characteristic of a wave that is responsible for what you c. Amplitude
interpret as pitch is the wave d. Wavelength
a. amplitude. 41. An airplane pilot hears a slow beat from the two engines of
b. shape. his plane. He increases the speed of the right engine and now
c. frequency. hears a slower beat. What should the pilot now do to eliminate
d. height. the beat?
32. Sound waves travel faster in a. Increase the speed of the left engine.
a. solids as compared to liquids. b. Decrease the speed of the right engine.
b. liquids as compared to gases. c. Increase the speed of both engines.
c. warm air as compared to cooler air. d. Increase the speed of the right engine.
d. All of the above are correct. 42. Resonance occurs when an external force matches the
33. The difference between an echo and a reverberation is a. interference frequency.
a. an echo is a reflected sound; reverberation is not. b. decibel frequency.
b. the time interval between the original sound and the c. beat frequency.
reflected sound. d. natural frequency.
c. the amplitude of an echo is much greater. 43. The sound quality is different for the same-pitch note produced
d. reverberation comes from acoustical speakers; echoes come by two different musical instruments, but you are
from cliffs and walls. able to recognize the basic note because of the same
34. Sound interference is necessary to produce the phenomenon a. harmonics.
known as b. fundamental frequency.
a. resonance. c. node positions.
b. decibels. d. standing waves.
c. beats.
d. reverberation.
136 CHAPTER 5 Wave Motions and Sound 5-22