Question 1

The speed of sound in dry air at 20ºC is 343 m/s.The speed of sound in dry air at 80ºC is

Accepted Answer

A) 86.0 m/s 
B) 172 m/s 
C) 377 m/s 
D) 686 m/s 
E) 1.27 km/s 
A) 86.0 m/s 
B) 172 m/s 
C) 377 m/s 
D) 686 m/s 
E) 1.27 km/s

Question 2

Which of the following wavefronts results from a supersonic flight?

Accepted Answer

A) (1) 
B) (2) 
C) (3) 
D) (1)and (3) 
E) they are all supersonic 
A) (1) 
B) (2) 
C) (3) 
D) (1)and (3) 
E) they are all supersonic

Question 3

A string under tension carries a transverse wave traveling at speed v.If the tension in the string is halved,what is the wave speed?

Accepted Answer

A) The wave speed is unchanged. 
B) The wave speed is halved. 
C) The wave speed is quadrupled. 
D) The wave speed decreases to about 71% of v. 
E) The wave speed increases by about 41%. 
A) The wave speed is unchanged. 
B) The wave speed is halved. 
C) The wave speed is quadrupled. 
D) The wave speed decreases to about 71% of v. 
E) The wave speed increases by about 41%.

Question 4

While you are standing on a corner,a police car with a 1-kHz siren drives past you at 30 m/s with its siren on.The speed of sound is 340 m/s.After the car has passed,the frequency you hear is about

Accepted Answer

A) 1.10 kHz 
B) 1.09 kHz 
C) 1.00 kHz 
D) 919 Hz 
E) 912 Hz 
A) 1.10 kHz 
B) 1.09 kHz 
C) 1.00 kHz 
D) 919 Hz 
E) 912 Hz

Question 5

A musical pitch is played at 60 dB.Another is played that sounds four times as loud.The sound intensity level of the second pitch is

Accepted Answer

A) 80 dB 
B) 100 dB 
C) 66 dB 
D) 64 dB 
E) 240 dB 
A) 80 dB 
B) 100 dB 
C) 66 dB 
D) 64 dB 
E) 240 dB

Question 6

Which curve best represents the variation of wave velocity with tension in a vibrating string?

Accepted Answer

A) 1 
B) 2 
C) 3 
D) 4 
E) 5 
A) 1 
B) 2 
C) 3 
D) 4 
E) 5

Question 7

If you were to double the amplitude of a wave on a string while keeping the speed and frequency of the wave constant,the energy delivered by the wave would

Accepted Answer

A) double. 
B) quadruple. 
C) be reduced 50%. 
D) be reduced to 25% of its previous value. 
E) be unchanged. 
A) double. 
B) quadruple. 
C) be reduced 50%. 
D) be reduced to 25% of its previous value. 
E) be unchanged.

Question 8

The angle of the shock wave produced by a jet traveling at Mach 2 at an altitude of 3000 m (assume the speed of sound to be 340 m/s at this altitude)is approximately

Accepted Answer

A) 30º 
B) 40º 
C) 50º 
D) 60º 
E) 80º 
A) 30º 
B) 40º 
C) 50º 
D) 60º 
E) 80º

Question 9

The speed of sound in air at 0ºC is 331 m/s.What is the speed of sound in air at -40ºC?

Accepted Answer

A) 241 m/s 
B) 282 m/s 
C) 306 m/s 
D) 309 m/s 
E) 379 m/s 
A) 241 m/s 
B) 282 m/s 
C) 306 m/s 
D) 309 m/s 
E) 379 m/s

Question 10

Which of the following function is NOT a possible wave equation? A and c are constants.The other symbols have their usual meaning.

Accepted Answer

A) y(x,t)= 1/(x - vt) 
B) y(x,t)= A e-vxt/c  
C)    
D) y(x,t)= A cos (kx)sin (ωt) 
E) y(x,t)= A sin(kx + ωt) 
A) y(x,t)= 1/(x - vt) 
B) y(x,t)= A e-vxt/c  
C)    
D) y(x,t)= A cos (kx)sin (ωt) 
E) y(x,t)= A sin(kx + ωt)

Question 11

The graph shows a wave moving from left to right.If the period of this wave motion is 50 ms,the wave is moving with a velocity of

Accepted Answer

A) 40$\pi$ cm/s 
B) 1.6$\pi$ m/s 
C) 1.6 m/s 
D) 80 cm/s 
E) 0.40 cm/s 
A) 40$\pi$ cm/s 
B) 1.6$\pi$ m/s 
C) 1.6 m/s 
D) 80 cm/s 
E) 0.40 cm/s

Question 12

A wave is traveling with a speed v along the x axis in the positive direction.The upper graph shows the displacement y versus the distance x for a given instant of time.The lower graph shows the displacement y versus the time t for any given point x.From the information in the graphs,what is the wave speed v?

Accepted Answer

A) 8.0 m/s 
B) 4.0 m/s 
C) 6.0 m/s 
D) There is not enough information to solve the problem. 
E) None of these is correct. 
A) 8.0 m/s 
B) 4.0 m/s 
C) 6.0 m/s 
D) There is not enough information to solve the problem. 
E) None of these is correct.

Question 13

Increasing the temperature,expressed in kelvins,in a gas by 125% will produce an increase in the speed of sound in the gas of approximately

Accepted Answer

A) 25% 
B) 18% 
C) 12% 
D) 9% 
E) 4% 
A) 25% 
B) 18% 
C) 12% 
D) 9% 
E) 4%

Question 14

If you were to reduce the frequency of a wave on a string by a factor of 2 while keeping the speed and amplitude of the wave constant,the rate at which energy is delivered by the wave would

Accepted Answer

A) double. 
B) quadruple. 
C) be reduced 50%. 
D) be reduced to 25% of its previous value. 
E) be unchanged. 
A) double. 
B) quadruple. 
C) be reduced 50%. 
D) be reduced to 25% of its previous value. 
E) be unchanged.

Question 15

A string is stretched by a force of 4.0 N.The mass per unit length of the string is 4.0 $\times$ 10-4 kg/m.A transverse wave would travel along this string with a velocity of approximately

Accepted Answer

A) 0.80 cm/s 
B) 2.0 cm/s 
C) 8.0 cm/s 
D) 50 m/s 
E) 1.0 F1F1F1S1F1F1F10 102 m/s 
A) 0.80 cm/s 
B) 2.0 cm/s 
C) 8.0 cm/s 
D) 50 m/s 
E) 1.0 F1F1F1S1F1F1F10 102 m/s

Question 16

In a seismic event,two types of waves are created,a P-wave (longitudinal)and an S-wave (transverse).The waves travel at speeds of 8 km/s and 5 km/s respectively.At a monitoring station,a P-wave is observed 10 s before the S-wave.How far is the seismic activity from the station? Assume that the waves travel in a straight line.

Accepted Answer

A) 50 km 
B) 80 km 
C) 30 km 
D) 133 km 
E) none of the above 
A) 50 km 
B) 80 km 
C) 30 km 
D) 133 km 
E) none of the above

Question 17

A police car siren emits a sound at 600 Hz.If an observer moves toward the source at 50 km/hr and hears a siren frequency of 678 Hz,calculate the speed of the police car and whether it is approaching or receding from the observer (assume the speed of sound in air = 343 m/s).

Accepted Answer

A) 99.0 km/hr receding 
B) 144 km/hr approaching 
C) 99.0 km/hr approaching 
D) 144 km/hr receding 
E) not possible for any reasonable police car speed 
A) 99.0 km/hr receding 
B) 144 km/hr approaching 
C) 99.0 km/hr approaching 
D) 144 km/hr receding 
E) not possible for any reasonable police car speed

Question 18

A noisy workplace has a noise level of 90 dB.You want to reduce this to a more comfortable 75 dB.By what factor must the power of the noise source be reduced? (That is,what is the ratio of the new power to the old?)

Accepted Answer

A) 0.83 
B) 0.67 
C) 0.32 
D) 0.032 
E) 0.010 
A) 0.83 
B) 0.67 
C) 0.32 
D) 0.032 
E) 0.010

Question 19

In which of the following is the speed of sound greatest?

Accepted Answer

A) air 
B) water 
C) a vacuum 
D) wood 
E) steel 
A) air 
B) water 
C) a vacuum 
D) wood 
E) steel

Question 20

The sound intensity in front of a loudspeaker diaphragm vibrating at 2 kHz is 4.3 W/m2,with an acoustic power output of 0.3 W.Calculate the diameter of the diaphragm.

Accepted Answer

A) 3 cm 
B) 9 cm 
C) 15 cm 
D) 30 cm 
E) 60 cm 
A) 3 cm 
B) 9 cm 
C) 15 cm 
D) 30 cm 
E) 60 cm

Exam 15: Wave Motion

The speed of sound in dry air at 20ºC is 343 m/s.The speed of sound in dry air at 80ºC is

Which of the following wavefronts results from a supersonic flight?

A string under tension carries a transverse wave traveling at speed v.If the tension in the string is halved,what is the wave speed?

While you are standing on a corner,a police car with a 1-kHz siren drives past you at 30 m/s with its siren on.The speed of sound is 340 m/s.After the car has passed,the frequency you hear is about

A musical pitch is played at 60 dB.Another is played that sounds four times as loud.The sound intensity level of the second pitch is

Which curve best represents the variation of wave velocity with tension in a vibrating string?

If you were to double the amplitude of a wave on a string while keeping the speed and frequency of the wave constant,the energy delivered by the wave would

The angle of the shock wave produced by a jet traveling at Mach 2 at an altitude of 3000 m (assume the speed of sound to be 340 m/s at this altitude)is approximately

The speed of sound in air at 0ºC is 331 m/s.What is the speed of sound in air at -40ºC?

Which of the following function is NOT a possible wave equation? A and c are constants.The other symbols have their usual meaning.

The graph shows a wave moving from left to right.If the period of this wave motion is 50 ms,the wave is moving with a velocity of

Increasing the temperature,expressed in kelvins,in a gas by 125% will produce an increase in the speed of sound in the gas of approximately

If you were to reduce the frequency of a wave on a string by a factor of 2 while keeping the speed and amplitude of the wave constant,the rate at which energy is delivered by the wave would

A string is stretched by a force of 4.0 N.The mass per unit length of the string is 4.0 ×\times× 10-4 kg/m.A transverse wave would travel along this string with a velocity of approximately

A police car siren emits a sound at 600 Hz.If an observer moves toward the source at 50 km/hr and hears a siren frequency of 678 Hz,calculate the speed of the police car and whether it is approaching or receding from the observer (assume the speed of sound in air = 343 m/s).

A noisy workplace has a noise level of 90 dB.You want to reduce this to a more comfortable 75 dB.By what factor must the power of the noise source be reduced? (That is,what is the ratio of the new power to the old?)

In which of the following is the speed of sound greatest?

The sound intensity in front of a loudspeaker diaphragm vibrating at 2 kHz is 4.3 W/m2,with an acoustic power output of 0.3 W.Calculate the diameter of the diaphragm.

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A string is stretched by a force of 4.0 N.The mass per unit length of the string is 4.0 $\times$ 10^-4 kg/m.A transverse wave would travel along this string with a velocity of approximately

The sound intensity in front of a loudspeaker diaphragm vibrating at 2 kHz is 4.3 W/m²,with an acoustic power output of 0.3 W.Calculate the diameter of the diaphragm.