Kaplan MCAT Physics and Math Review 2019-2020

Kaplan

Chapter 7

Waves and Sound

Educators

Chapter Questions

Problem 1

An opera singer has two precisely identical glasses. The singer
produces as pure a tone as possible and shatters the first glass at a
frequency of $808 \mathrm{Hz}$. She then sings a frequency of $838 \mathrm{Hz}$ in the
presence of the second glass. The second glass will likely:
(A) $\quad$ shatter after a longer amount of time because the applied
frequency is higher.
(B) shatter after a shorter amount of time because the applied
frequency is higher.
$(C)$
not shatter because the applied frequency is not equal to
the natural frequency of the glass.
(D) $\quad$ not shatter because higher-frequency sounds are
associated with more attenuation.

Averell Hause

Averell Hause

Carnegie Mellon University

Problem 2

A child is practicing the first overtone on his flute. If his brother
covers one end of the flute for a brief second, how will the sound
change, assuming that the new pitch represents the first overtone
in the new setup?
(A) $\quad$ The pitch of the sound will go up.
(B) $\quad$ The pitch of the sound will go down.
(C) $\quad$ The pitch of the sound will not change.
(D) $\quad$ The change in the pitch depends on the starting pitch.

Averell Hause

Carnegie Mellon University

Problem 3

Which of the following is necessarily true regarding frequency,
angular frequency, and period of a given wave?
(A) $\quad$ The magnitude of the angular frequency is larger than the
magnitude of the period.
(B) $\quad$ The product of the frequency and period is equal to the
angular frequency.
(C) $\quad$ The magnitude of the angular frequency is larger than the
magnitude of the frequency.
(D) $\quad$ The product of the angular frequency and period is 1

Averell Hause

Carnegie Mellon University

Problem 4

Ultrasound machines calculate distance based upon:
(A) $\quad$ intensity of the reflected sound.
(B) travel time of the reflected sound.
(C) $\quad$ angle of incidence of the sound.
(D) $\quad$ the detected frequency of the sound.

Averell Hause

Carnegie Mellon University

Problem 5

The period for a certain wave is 34 ms. If there is a Doppler shift that doubles the perceived frequency, which of the following must
be true?

The detector is moving toward the source at a velocity equal
to the speed of sound.

The source is moving toward the detector at a velocity equal to half the speed of sound.
The perceived period is $17 \mathrm{ms}$
The perceived period is $68 \mathrm{ms}$
(A) III only
(B) $\quad$ I and IV only
(C) II and III only
(D) $\quad$ I $,$ II, and IV only

Averell Hause

Carnegie Mellon University

Problem 6

If the speed of a wave is $5 \frac{\mathrm{m}}{\mathrm{s}}$ and its wavelength is $10 \mathrm{cm},$ what is
its period?
(A) $0.01 s$
(B) $0.03 \mathrm{s}$
$(C)$
$0.1 \mathrm{s}$
(D) $0.3 \mathrm{s}$

Averell Hause

Carnegie Mellon University

Problem 7

What is the angular frequency of the third harmonic in a pipe of
length $1.5 \mathrm{m}$ with one closed end? (Note: The speed of the sound is approximately $\left.100 \frac{\mathrm{m}}{\mathrm{s}},\right)$
(A) 170 radians per second
(B) $\quad 170 \pi$ radians per second
(C) $\quad 340$ radians per second
(D) $\quad 340 \pi$ radians per second

Averell Hause

Carnegie Mellon University

Problem 8

A certain sound level is increased by $20 \mathrm{dB}$. By what factor does its
intensity increase?
(A) 2
(B) 20
(C) $\quad 100$
(D) $\quad \log 2$

Averell Hause

Carnegie Mellon University

Problem 9

In some forms of otosclerosis, the stapedial foot plate, which
transmits vibrations from the bones of the middle ear to the fluid
within the cochlea, can become fixed in position. This limits the
displacement of the stapedial foot plate during vibration. Based on this mechanism, which of the following symptoms would most
likely be seen in an individual with otosclerosis?
(A) $\quad$ An increase in the perceived volume of sounds
(B) $\quad$ A decrease in the perceived volume of sounds
(C) $\quad$ An increase in the perceived pitch of sounds
(D) $\quad$ A decrease in the perceived pitch of sounds

Averell Hause

Carnegie Mellon University

Problem 10

If two waves with the same frequency are $180^{\circ}$ out of phase, what is
the amplitude of the resultant wave if the amplitudes of the
original waves are $5 \mathrm{cm}$ and $3 \mathrm{cm} ?$
(A) $2 \mathrm{cm}$
(B) $3 \mathrm{cm}$
(C) $\quad 5 \mathrm{cm}$
(D) $8 \mathrm{cm}$

Averell Hause

Carnegie Mellon University

Problem 11

A student is measuring sound frequencies from the side of a road while walking east. For which of the following situations could the student determine that the difference between the perceived
frequency and the actual emitted frequency is zero?
(A) A plane flying directly above him from east to west
(B) $\quad$ A police car passing the student with its siren on
(C) $\quad$ A person playing piano in a house on the street
(D) $\quad$ A dog barking in a car that moves east

Averell Hause

Carnegie Mellon University

Problem 12

In which of the following media does sound travel the fastest?
$(A)$
Vacuum
(B) Air
$(C)$
Water
(D) Glass

Averell Hause

Carnegie Mellon University

Problem 13

Shock waves have the greatest impact when the source is traveling:
(A) $\quad$ just below the speed of sound.
(B) $\quad$ exactly at the speed of sound.
(C) just above the speed of sound.
(D) $\quad$ well above the speed of sound.

Averell Hause

Carnegie Mellon University

Problem 14

As an officer approaches a student who is studying with his radio playing loudly beside him, he experiences the Doppler effect. Which of the following statements remains true while the officer
moves closer to the student?
The apparent frequency of the music is increased.
The same apparent frequency would be produced if the
officer were stationary and the student approached him at the
same speed.
The apparent velocity of the wave is decreased.
(A) $\quad$ I only
(B) $\quad \|$ only
(C) $\quad$ I and III only
(D) $\quad$ ?, II, and III

Averell Hause

Carnegie Mellon University

Problem 15

Ignoring attenuation, how does the intensity of a sound change as
the distance from the source doubles?
(A) $\quad$ It is four times as intense.
(B) $\quad$ It is twice as intense.
(C) It is half as intense.
(D) $\quad$ It is one-quarter as intense.

Averell Hause

Carnegie Mellon University

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