OPAC 102 First Midterm Exam
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(Duration: 𝟑 hour)
A. Choose the correct answer.
1. If the particles of the medium are vibrating to and fro in the same direction of energy transport, then the wave is a
____ wave.
a) longitudinal
b) sound
c) standing
d) transverse
2. What is the frequency of a wave that has a speed of 0.4 m/s and a wavelength of 0.020 meter?
a) 10 hertz.
b) 20 hertz.
c) 0.008 hertz.
d) 0.5 hertz.
3. An object is vibrating at its natural frequency. Repeated and periodic vibrations of the same natural frequency
impinge upon the vibrating object and the amplitude of its vibrations are observed to increase. This phenomenon is
known as ____.
a. beats
b. fundamental
c. interference
d. overtone
e. resonance
4. A standing wave experiment is performed to determine the speed of waves in a rope. The standing wave pattern
shown below is established in the rope. The rope makes exactly 90 complete vibrational cycles in one minute. The
speed of the waves is ____ m/s.
a) 3.0
b) 6.0
c) 180
d) 360
5. Consider the standing wave pattern shown below. A wave generated at the left end of the medium undergoes
reflection at the fixed end on the right side of the medium. The number of antinodes in the diagram is _____.
a) 3
b) 5
c) 6
d) 7
6. Which phenomenon is produced when two or more waves passing simultaneously through the same medium meet
up with one another?
a) refraction
b) diffraction
c) interference
d) reflection
7. What do seismic waves and sound waves have in common?
a) they are mechanical waves
b) they are electromagnetic waves
c) they are phonetic waves
d) they are permanent waves
8. In order for two sound waves to produce audible beats, it is essential that the two waves have ____.
a) the same amplitude b) the same frequency c) slightly different amplitudes d) slightly different frequencies
9. A traveling periodic wave passes a point of observation. At this point, the time between successive crests is 0.2s.
What can you say about this wave?
a) The wavelength is 5 m
b) The frequency is 5 Hz c) The velocity is 5 m/s d) The period is 0.4 s
10.A stretched string vibrates with a fundamental frequency of 100 Hz. The frequency of the second harmonic is ___.
a) 25.0 Hz
b) 50.0 Hz
c) 100. Hz
d) 200. Hz
11. A sound wave is a mechanical wave, not an electromagnetic wave. This means that
a) particles of the medium move perpendicular to the direction of energy transport.
b) a sound wave transports its energy through a vacuum.
c) particles of the medium regularly and repeatedly oscillate about their rest position.
d) a medium is required in order for sound waves to transport energy.
12. A sound wave is a
a) transverse wave caused by the compression of particles b) transverse wave that passes through a vacuum
c) longitudinal wave produced by the motion of water
d) longitudinal wave caused by the vibration of a medium
13. To increase the loudness of a sound, you should
a) decrease the amount of energy in it b) decrease its wavelength c) increase its intensity d) increase its speed
14.
a) the medium to the left of the boundary is denser than the medium to the right.
b) the medium to the right of the boundary is denser than the medium to the left.
c) the wavelength of the transmitted wave is less than the wavelength of the reflected wave.
d) there is a flaw in the drawing. Incident and reflected pulses should have the same height.
15. Which of the following statements are TRUE (T) or FALSE (F)?
(…) Sound can travel through a vacuum.
(…) A sound wave is a pressure wave; they can be thought of as fluctuations in pressure with respect to time.
(…) The intensity of a sound wave has units of Watts/meter.
(…) When a sound wave is said to be intense, it means that the particles are vibrating back and forth at a high
frequency.
(…) A high pitched sound has a low wavelength.
(…) Ultrasound waves are those sound waves with frequencies less than 20 Hz.
(…) The result of two objects vibrating in resonance with each other is a vibration of larger amplitude.
(…) Open-end air columns can only produce even-numbered harmonics.
(…) A closed-end air column that can play a fundamental frequency of 250 Hz cannot play 500 Hz.
(…) A more rigid material such as steel has a higher elasticity and therefore sound tends to move through it at high
speeds.
B. Solve the following problems.
1. A 50.0-g object connected to a spring with a force constant of 35.0 N/m oscillates on a horizontal, frictionless
surface with an amplitude of 4.00 cm. Find (a) the total energy of the system and (b) the speed of the object when the
position is 1.00 cm. Find (c) the kinetic energy when the position is 3.00 cm.
2. A 10.6-kg object oscillates at the end of a vertical spring that has a spring constant of 2.05 x 104 N/m. The effect of
air resistance is represented by the damping coefficient b =3.00 N. s/m. (a) Calculate the frequency of the damped
oscillation. (b) By what percentage does the amplitude of the oscillation decrease in each cycle?
3. The tensile stress in a thick copper bar is 99.5% of its elastic breaking point of 13.0 x10 10 N/m2. If a 500-Hz sound
wave is transmitted through the material. (a) What displacement amplitude will cause the bar to break? (b) What is
the maximum speed of the elements of copper at this moment? (c) What is the sound intensity in the bar?
4. Sinusoidal waves 5.00 cm in amplitude are to be transmitted along a string that has a linear mass density of 4.00
x10-2 kg/m. If the source can deliver a maximum power of 300 W and the string is under a tension of 100 N, what is
the highest frequency at which the source can operate?
5. Transverse waves travel with a speed of 20.0 m/s in a string under a tension of 6.00 N. What tension is required for
a wave speed of 30.0 m/s in the same string?
6. A vacuum cleaner produces sound with a measured sound level of 70.0 dB. (a) What is the intensity of this sound
in W/m2? (b) What is the pressure amplitude of the sound?
7. Standing at a crosswalk, you hear a frequency of 560 Hz from the siren of an approaching ambulance. After the
ambulance passes, the observed frequency of the siren is 480 Hz. Determine the ambulance’s speed from these
observations.
8. A 60.000-cm guitar string under a tension of 50.000 N has a mass per unit length of 0.100 00 g/cm. What is the
highest resonant frequency that can be heard by a person capable of hearing frequencies up to 20 000 Hz?
C. Write the answers of following problems.
1. Explain the types of sound in briefly by drawing ultransonics range diagram.
2. What is the meaning of resonance, damping force and driven force? Give an example.