Question 1

While enjoyable,rock concerts can be damaging to one's hearing.If you are sitting in the front row of a rock concert 5 m from the speaker system,and the sound intensity is 120 dB,how far back would you have to be such that the sound intensity drops below the recommended safe level of 90 dB?

Accepted Answer

A) 7 m 
B) 9 m 
C) 90 m 
D) 100 m 
E) 160 m

Question 2

A police car siren emits a high frequency tone with a beat frequency of 10 Hz.What happens to the sound as heard by a stationary observer as the car approaches the observer?

Accepted Answer

A) The siren tone increases in frequency while the beat frequency decreases. 
B) The siren tone decreases in frequency while the beat frequency increases. 
C) Both the siren tone and the beat frequency increase. 
D) Both the siren tone and the beat frequency decrease. 
E) The siren tone increases while the beat frequency remains unchanged.

Question 3

A bugle can be represented by a cylindrical pipe of length L = 1.24 m.Since the ends are open,the boundary conditions force the standing wave (representing the displacement of the air molecules)that is produced in the bugle to have antinodes at the open ends of the bugle,where the air molecules move back and forth the most.The longest wavelength standing wave inside the bugle is

Accepted Answer

A) 0.620 m. 
B) 1.24 m. 
C) 2.48 m. 
D) 3.78 m. 
E) 4.96 m.

Question 4

You drop a stone down a well.After 2.45 s you hear the splash.How deep is the well? The speed of sound in air is 343 m/s.

Accepted Answer

A) 9.50 m 
B) 12.8 m 
C) 18.2 m 
D) 21.3 m 
E) 27.5 m

Question 5

You are sitting near the back of a twin-engine commercial jet airliner,which has the engines mounted on the fuselage near the tail.The nominal rotation speed for the turbofan in each engine is 5200 revolutions per minute,which is also the frequency of the dominant sound emitted by the engine.If one engine is running at 5214 revolutions per minute and the other at 5385 revolutions per minute,the passengers hear a pulsing noise that repeats every

Accepted Answer

A) 5.8 * 10-3 s 
B) 0.35 s 
C) 0.70 s 
D) 0.18 s 
E) 0.025 s

Question 6

What is the speed of sound in air if its temperature is -10oC?

Accepted Answer

A) 319 m/s 
B) 337 m/s 
C) 325 m/s 
D) 331 m/s

Question 7

A pianist considers two strings in the piano that are side-by-side.Their construction is identical in terms of their linear mass density and tension-only the length is different.If,when the strings are vibrating in their fundamental modes,a beat frequency of 2.0Hz is heard,and if the average frequency heard is 111Hz,what is the ratio of lengths of the higher frequency to lower frequency string?

Accepted Answer

A) 1.04 
B) 1.02 
C) 1.00 
D) 0.98 
E) 0.96

Question 8

An airplane approaches an airport control tower which is emitting a sound at 3000 Hz.The frequency heard in the plane is 4250 Hz.At what fraction of the speed of sound is the plane traveling?

Accepted Answer

A) 0.12 
B) 0.24 
C) 0.29 
D) 0.36 
E) 0.42

Question 9

Two identical closed-open pipes each have a fundamental frequency of 500 Hz.If the length of one of the pipes is increased by 1% What is the beat frequency when they are sounded simultaneously?

Accepted Answer

A) 2 Hz 
B) 8 Hz 
C) 10 Hz 
D) 13 Hz 
E) 5 Hz

Question 10

My home is exactly 5.9 km from Spartan Stadium,where the football team has just scored another touchdown.Since the game is broadcast live,I can see the touchdown on TV,essentially without time delay.The time difference between when I see the touchdown and when I hear the roar from the stadium is 16.9 s.What is the temperature (in degrees Celsius)of the air?

Accepted Answer

A) 30.2S1U1P1$\circ$S1S1P0C 
B) 25.2S1U1P1$\circ$S1S1P0C 
C) 20.2S1U1P1$\circ$S1S1P0C 
D) 15.2S1U1P1$\circ$S1S1P0C 
E) 10.2S1U1P1$\circ$S1S1P0C

Question 11

A standing wave in a column of air with both ends open has a frequency of 600 Hz.The next higher harmonic has a frequency of 800 Hz.What is the fundamental frequency?

Accepted Answer

A) 100 Hz 
B) 132 Hz 
C) 200 Hz 
D) 215 Hz 
E) 285 Hz

Question 12

An open organ pipe has two adjacent natural frequencies of 500 and 600 Hz.Assume the speed of sound in air 340 m/s.The length of the organ pipe is

Accepted Answer

A) 0.11 m. 
B) 0.56 m. 
C) 0.81 m. 
D) 1.1 m. 
E) 1.7 m.

Question 13

A driver approaches a stationary 440 Hz siren at 25 m/s.What is the frequency heard by the driver?

Accepted Answer

A) 472 Hz 
B) 440 Hz 
C) 408 Hz 
D) 412 Hz 
E) 431 Hz

Question 14

A source travelling to the right at a speed of 10 m/s emits a sound wave at a frequency of 100 Hz.The sound wave is reflected off a reflector which is travelling to the left at a speed of 5 m/s.What is the frequency of the reflected sound wave detected by a listener back at the source?

Accepted Answer

A) 105 Hz 
B) 104 Hz 
C) 109 Hz 
D) 96 Hz 
E) 91 Hz

Question 15

While standing on a sidewalk,you notice that you are halfway between a clock tower and a large building.The clock tower and the building are 170 m apart.When the clock bell strikes the hour,you hear an echo of the bell after hearing it directly from the clock tower.How long after hearing the bell from the clock tower do you hear the echo?

Accepted Answer

A) 0.50 s 
B) 0.33 s 
C) 0.25 s 
D) 0.60 s 
E) 0.75 s

Question 16

You are a fireworks-launcher,and launch a fireworks shell into the air directly above you with an initial speed of 227 m/s.If it explodes at the top of its trajectory,how long after launch do you hear the explosion? Assume 343 m/s for the speed of sound.

Accepted Answer

A) 23.1 s 
B) 30.8 s 
C) 38.6 s 
D) 46.1 s 
E) None are correct.

Question 17

Paul stands exactly halfway between two sound sources,one of which emits with twice the power of the other.What is the relative intensity factor (in dB)of the two sources at the point where Paul stands?

Accepted Answer

A) 0 dB 
B) 1.0 dB 
C) 2.0 dB 
D) 3.0 dB 
E) 4.0 dB

Question 18

The sound level when one student is talking during lecture is 40.0 dB.What would be the sound level if all 256 students talk at the same time during lecture? Assume each student talks equally loudly.

Accepted Answer

A) 42.4 dB 
B) 64.1 dB 
C) 65.6 dB 
D) 296 dB

Question 19

Standing on the sidewalk we listen to the sound of the horn of a passing car.As the car passes us,the frequency of the sound changes from high to low in a continuous manner,that is,there is no abrupt change in the frequency heard.This is because

Accepted Answer

A) the pitch of the sound of horn changes continuously. 
B) the intensity of the sound heard changes continuously. 
C) we are not standing directly in the path of the traveling car. 
D) All of the reasons contribute to the heard effect.

Question 20

You stand on the curb waiting to cross the street.Suddenly you hear the sound of a horn from a car approaching you with a constant speed of 25.0 m/s.You hear a frequency of 100 Hz.After the car passes you by,what is the frequency that you will hear?

Accepted Answer

A) 86.4 Hz 
B) 91.0 Hz 
C) 109 Hz 
D) 115 Hz 
E) 120 Hz

Exam 16: Sound