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Chs 16-17 Sample Multiple Choice Questions – Mechanical Waves
Note: Unless otherwise noted, use g = 10 m/s2 and neglect air resistance.
1.
A longitudinal wave is distinguished from a transverse wave by the fact that in longitudinal waves
(A) energy is transported from one point in space to another point.
(B) energy is not transported from one point in space to another point.
(C) the particle vibration is parallel to the direction of propagation.
(D) the particle vibration is perpendicular to the direction of propagation.
Use the following diagram of a wave to answer questions 2-4:
2.
3.
4.
The wavelength of the wave is
(A) 0.5 m (B) 1.0 m (C) 2.0 m
(D) 4.0 m
(E) 6.0 m
The amplitude of the wave is
(A) 0.5 m (B) 1.0 m (C) 2.0 m
(D) 4.0 m
(E) 6.0 m
The frequency of the wave is
(A) 2.0 Hz (B) 3.0 Hz (C) 1.5 Hz
(D) 0.5 Hz
(E) 1.0 Hz
5.
A girl on the beach watching water waves sees 4 waves pass by in 2 seconds, each with a wavelength of 0.5 m. The speed
of the waves is
(A) 0.25 m/s (B) 0.5 m/s (C) 1.0 m/s (D) 2.0 m/s (E) 4.0 m/s
6.
As a wave passes from a spring to another spring with a greater tension,
(A) the speed of the wave decreases
(B) the frequency of the wave increases.
(C) the frequency of the wave decreases. (D) the amplitude of the wave increases
(E) the speed of the wave increases.
7.
Six seconds after a brilliant flash of lightning, thunder shakes the house. Approximately how far was the lightning strike
from the house?
(A) much closer than one kilometer
(B) about one kilometer away
(C) about two kilometers away
(D) much farther away than two kilometers
8.
A railroad whistle is sounded. An echo is heard 5.0 seconds later. If the speed of sound is 343 m/s, how far away is the
reflecting surface?
(A) 68 m (B) 140 m (C) 860 m (D) 1700 m
9.
An earthquake generates three kinds of waves: surface waves (L-waves), which are the slowest and weakest, shear (S)
waves, which are transverse waves and carry most of the energy, and pressure (P) waves, which are longitudinal waves
and are the fastest. The speed of P waves is approximately 7 km/s, and that of S waves is about 4 km/s. People do not
generally feel the P waves, but animals seem to be sensitive to them. If a person reports that her dog started barking 20
seconds "before the earthquake," then approximately how far was the origin of the earthquake?
(A) 100 km (B) 200 km (C) 300 km (D) 400 km
10. Why does the intensity of waves from a small source decrease with the square of the distance from the source?
(A) The waves run out of energy as they travel.
(B) The waves spread out as they travel.
(C) The medium through which the waves travel absorbs the energy of the waves.
(D) The waves slow down as they travel away from the source.
11. Sound A has a higher pitch than sound B. Which of the following statements about these two sounds are correct? (There
could be more than one correct choice.)
(A) The wavelength of A is longer than the wavelength of B.
(B) The period of A is shorter than the period of B.
(C) The frequency of A is greater than the frequency of B.
(D) Sound B travels faster than sound B through air.
(E) The amplitude of A is larger than the amplitude of B.
12. The Doppler effect produces apparent changes in
(A) loudness (B) frequency (C) amplitude (D) velocity
(E) acceleration
13. A car’s horn emits a constant frequency as it accelerates away from a stationary listener. Which of the following quantities
actually changes for the listener?
I. frequency of the sound II. pitch of the sound III. amplitude of the sound IV. loudness of the sound
(A) I only (B) I and II only (C) III and IV only (D) II and IV only (E) I, II, III, and IV
14. In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream
as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the top of the cliff
leaning over the edge, the pitch of the scream as he falls should be
(A) higher than the original pitch and constant. (B) higher than the original pitch and increasing as he falls.
(C) lower than the original pitch and constant. (D) lower than the original pitch and decreasing as he falls.
15. The figure above shows two wave pulses that are approaching each other. Which of the following best shows the shape of
the resultant pulse when the centers of the pulses, points P and Q. coincide?
16. One end of a horizontal string is fixed to a wall. A transverse wave pulse is generated at
the other end, moves toward the wall as shown right, and is reflected at the wall. Which
of the following statements concerning the reflected pulse is correct?
(A) The speed of the reflected pulse is greater than the speed of the incident pulse.
(B) The reflected pulse is on the opposite side of the string from the incident pulse.
(C) The wavelength of the reflected pulse is greater than the wavelength of the incident pulse.
(D) The amplitude of the reflected pulse is greater than the amplitude of the incident pulse.
Use the following to answer questions 17-18:
A standing wave of frequency 60 Hz is set up on a string 75 cm long, as shown above.
17. What is the speed with which the waves propagate on the string?
(A) 30 m/s (B) 23 m/s (C) 15 m/s (D) 7.5 m/s (E) 5.0 m/s
18. What would be the lowest possible frequency of vibration of the string that would produce a standing wave?
(A) 30 Hz
(B) 20 Hz
(C) 10 Hz
(D) 5.0 Hz
(E) 1.0 Hz
19. A string fixed at both ends is vibrating in one of its harmonics. If we now increase only the frequency at which the string is
vibrating, which of the following characteristics do we also increase? (There could be more than one correct choice.)
(A) the speed of the traveling waves on the string
(B) the period of the traveling waves on the string
(C) the wavelength of the traveling waves on the string (D) the amplitude of the traveling waves on the string
(E) none of the above
20. A rope of length L is clamped at both ends. Which one of the following is not a possible wavelength for standing waves
on this rope?
(A) 4L (B) 2L (C) L (D) 2L/3 (E) L/2
21. Which of the following wavelengths would produce standing waves on a string approximately 3.5 m long?
(A) 2.33 m
(B) 2.85 m
(C) 3.75 m (D) 5.25 m
22. A musician stands outside in a field and plucks a string on an acoustic guitar. Standing waves will most likely occur in
which of the following media? Select two answers.
(A) The guitar string
(B) The air inside the guitar
(C) The air surrounding the guitar
(D) The ground beneath the musician
23. The figure above represents the 1st harmonic for an open pipe. If the length of the pipe is 40 cm, the wavelength of the
sound wave resonating inside the pipe is
(A) 10 cm (B) 20 cm (C) 40 cm (D) 80 cm (E) 160 cm
24. Which of the following is true of a sound that is resonating in a pipe which is closed at one end?
(A) Nodes are formed at both ends of the pipe.
(B) Antinodes are formed at both ends of the pipe.
(C) An antinode is formed at the closed end of the pipe and a node is formed at the open end.
(D) An antinode is formed at the open end of the pipe and a node is formed at the closed end.
25. A pipe of length L that is closed at one end and open at the other end is resonating at its fundamental frequency. Which
statement about the sound is correct?
(A) The wavelength is 4L and there is a displacement node at the pipe's open end.
(B) The wavelength is 4L and there is a displacement antinode at the pipe's open end.
(C) The wavelength is L and there is a displacement node at the pipe's open end.
(D) The wavelength is L and there is a displacement antinode at the pipe's open end.
26. A music tuner uses a 554-Hz C# tuning fork to tune the frequency of a musical instrument. If the tuner hears a beat
frequency of 2 Hz, what is the frequency of the instrument?
(A) It must be 556 Hz.
(B) It must be 552 Hz.
(C) It could be either 556 Hz or 552 Hz.
(D) It could be either 553 Hz or 555 Hz.
27. A person stands between two speakers driven by the same source. Each speaker produces a tone with a frequency of 200
Hz on a day when the speed of sound is 330 m/s. The person is 1.65 m from one speaker and 4.95 m from the other. What
type of interference does the person perceive?
(A) constructive
(B) destructive (C) both constructive and destructive (D) neither constructive nor destructive
28. A student connects one end of a string with negligible mass to an oscillator. The other end of the string is passed over a pulley
and attached to a suspended weight, as shown above. The student finds that a standing wave with one antinode is formed on the
string when the frequency of the oscillator is f0. The student then moves the oscillator to shorten the horizontal segment of
string to half its original length. At what frequency will a standing wave with one antinode now be formed on the string?
(A) f0/2 (B) f0 (C) 2f0 (D)There is no frequency at which a standing wave will be formed.
29. A radio speaker produces sound when a membrane called a diaphragm vibrates, as shown above. A person turns up the
volume on the radio. Which of the following aspects of the motion of a point on the diaphragm must increase?
(A) The maximum displacement only
(B) The average speed only
(C) Both the maximum displacement and the average speed
(D) Neither the maximum displacement nor the average speed
30. The figure above shows a block on a horizontal surface attached to two springs whose other ends are fixed to walls. A light
string attached to one side of the block initially lies straight across the surface, as shown above. The other end of the string is
free to move. There is significant friction between the block and the surface but negligible friction between the string and
the surface. The block is displaced a distance d and released from rest. Which of the following best represents the shape of
the string a short time later?
Answers
1. C
2. C
3. B
11. B,C 12. B 13. E
21. A
22. A,B 23. D
4. A
14. D
24. D
5. C
15. A
25. B
6. E
16. B
26. C
7. C
17. A
27. A
8. C
18. B
28. C
9. B
19. E
29. C
10. B
20. A
30. C