IMO Practice Test — Sound
14 Questions • 15 min • Olympiad level
15:00
Question 1 of 14
A wave travels at $330\,\text{m/s}$ with wavelength $0.55\,\text{m}$. Its frequency is
$500\,\text{Hz}$
$600\,\text{Hz}$
$550\,\text{Hz}$
$660\,\text{Hz}$
Explanation: $f=v/\lambda=330/0.55=600\,\text{Hz}$.
Question 2 of 14
If frequency doubles while speed stays constant, the wavelength becomes
doubled
halved
unchanged
four times
Explanation: From $v=f\lambda$, with $v$ fixed, $\lambda\propto1/f$, so it halves.
Question 3 of 14
A man hears an echo $1.5\,\text{s}$ after clapping near a wall ($v=340\,\text{m/s}$). The wall is
$255\,\text{m}$
$510\,\text{m}$
$340\,\text{m}$
$170\,\text{m}$
Explanation: $2d=340\times1.5=510$, so $d=255\,\text{m}$.
Question 4 of 14
A tuning fork makes $1024$ vibrations in $2\,\text{s}$. Its frequency is
$256\,\text{Hz}$
$1024\,\text{Hz}$
$2048\,\text{Hz}$
$512\,\text{Hz}$
Explanation: $f=1024/2=512\,\text{Hz}$.
Question 5 of 14
A SONAR pulse returns in $3\,\text{s}$ in water ($v=1400\,\text{m/s}$). The depth is
$2100\,\text{m}$
$4200\,\text{m}$
$1400\,\text{m}$
$700\,\text{m}$
Explanation: $2d=1400\times3=4200$, so $d=2100\,\text{m}$.
Question 6 of 14
The time period of a $250\,\text{Hz}$ source is
$0.04\,\text{s}$
$0.004\,\text{s}$
$4\,\text{s}$
$0.25\,\text{s}$
Explanation: $T=1/f=1/250=0.004\,\text{s}$.
Question 7 of 14
Sound takes $5\,\text{s}$ to travel a distance in air at $340\,\text{m/s}$. The distance is
$1700\,\text{m}$
$680\,\text{m}$
$340\,\text{m}$
$3400\,\text{m}$
Explanation: Distance $=v\times t=340\times5=1700\,\text{m}$.
Question 8 of 14
Which property is unchanged when sound passes from air into water?
speed
wavelength
amplitude
frequency
Explanation: Frequency is set by the source and stays constant across media.
Question 9 of 14
An echo is just barely heard at $17.2\,\text{m}$ when $v=344\,\text{m/s}$. The time gap is
$0.05\,\text{s}$
$0.1\,\text{s}$
$0.2\,\text{s}$
$1\,\text{s}$
Explanation: $t=2d/v=2\times17.2/344=0.1\,\text{s}$.
Question 10 of 14
If the speed of sound in air is $346\,\text{m/s}$ at $25\,^\circ\text{C}$, raising the temperature will
decrease the speed
increase the speed
not change the speed
make it zero
Explanation: The speed of sound in air increases with temperature.
Question 11 of 14
A wave has $T=0.01\,\text{s}$ and $\lambda=3.4\,\text{m}$. Its speed is
$34\,\text{m/s}$
$340\,\text{m/s}$
$3.4\,\text{m/s}$
$0.34\,\text{m/s}$
Explanation: $f=1/T=100\,\text{Hz}$; $v=f\lambda=100\times3.4=340\,\text{m/s}$.
Question 12 of 14
An elephant communicates over long distances using
ultrasound
infrasound
X-rays
audible whistles only
Explanation: Elephants produce infrasound below $20\,\text{Hz}$.
Question 13 of 14
If a sound's amplitude is increased without changing frequency, the sound becomes
higher pitched
lower pitched
louder
softer
Explanation: Greater amplitude means greater loudness; pitch is unchanged.
Question 14 of 14
A pulse of ultrasound takes $0.4\,\text{s}$ to return from a crack inside a steel rail ($v=6000\,\text{m/s}$). The crack is at depth
$1200\,\text{m}$
$2400\,\text{m}$
$600\,\text{m}$
$1200\,\text{km}$
Explanation: $2d=6000\times0.4=2400$, so $d=1200\,\text{m}$.