Exam 21: Mechanical Waves

An earthquake generates three kinds of waves: surface waves (L-waves),which are the slowest and weakest,shear (S)waves,which are transverse waves and carry most of the energy,and pressure (P)waves,which are longitudinal waves and are the fastest.The speed of P waves is approximately 7 km/s,and that of S waves is about 4 km/s.People do not generally feel the P waves,but animals seem to be sensitive to them.If a person reports that her dog started barking 20 seconds "before the earthquake," then approximately how far was the origin of the earthquake?

A sound of 40 decibels is

Two stereo speakers mounted 4.52 m apart on a wall emit identical sound waves.You are standing at the opposite wall of the room at a point directly between the two speakers.You walk 2.11 m parallel to the wall,to a location where you first notice that the sound intensity is essentially zero.If the wall along which you are walking is $10.7 \mathrm {~m}$ from the wall with the speakers,what is the wavelength of the sound waves? The walls are cushioned to absorb sound reflections.

A string of length 2.5 m is fixed at both ends.When the string vibrates at a frequency of 85 Hz,a standing wave with five loops is formed. (a)Determine the distance between two adjacent nodes. (b)Determine the wavelength of the waves that travel on the string. (c)Determine the speed of traveling waves on this string. (d)Determine the fundamental frequency of this string.

A violin with string length 32 cm and string density $1.5 \mathrm {~g} / \mathrm { cm }$ resonates in its fundamental with the first overtone of a 2.0-m organ pipe with one end closed and one end open.What is the tension in the string if the speed of sound in air is 344 m/s?

Two police cars have identical sirens that produce sound of frequency of 570 Hz.A stationary listener is standing between two cars.One car is parked and the other is approaching the listener and both have their sirens on.The listener measures 9.0 beats per second.Find the speed of the approaching police car.The speed of sound is 340 m/s.

In a resonating pipe that is open at both ends,there

Sonar is used to determine the speed of an object.A 40.0-kHz signal is sent out,and a 42.0-kHz signal is returned.If the speed of sound is 345 m/s,how fast is the object moving?

At a distance of 15.0 m from a sound source,the intensity level is 60.0 dB.What is the intensity level (in decibels)at a point 2.00 m from the source if the source radiates equally in all directions?

Find the speed of an ocean wave whose displacement is given by the equation $y = 3.7 \cos ( 2.2 x - 5.6 t )$ where x and y are in meters and t is in seconds.

A 15-m rope is pulled taut with a tension of 140 N.It takes 0.545 s for a wave to propagate along the rope.What is the mass of the rope?

A piano wire of linear mass density 0.0050 kg/m is under a tension of 1350 N.What is the wave speed in this wire?

Consider a pipe of length L that is open at both ends.What are the wavelengths of the three lowest-pitch tones produced by this pipe?

A string of length L is under tension,and the speed of a wave in the string is v.What will be the speed of a wave in the string if the length is increased to 2L but with no change in the mass or tension?

The vertical displacement y(x,t)of a horizontal string aligned along the x-axis is given by the equation y(x,t)= (6.00 mm)cos[(3.25 m^-1)x - (7.22 s^-1)t].What are the (a)speed and (b)amplitude of this wave?

The sound from the whistle of a truck moving at 17.0 m/s toward a cliff reflects from the cliff and is heard by the driver of the truck.When it is parked at the side of the road,the whistle from the truck produces sound of frequency 2.267 kHz.As observed by the driver of the truck,what is the change in frequency the sound from the whistle due to the reflection? The speed of sound is 343 m/s.

A string of linear density 1.5 g/m is under a tension of 20 N.What should be its length if its fundamental resonance frequency is 220 Hz?

A standing wave is oscillating at 950 Hz on a string,as shown in the figure.What is the wave speed?

Consider the standing wave on a guitar string and the sound wave generated by the string as a result of this vibration.What do these two waves have in common? (There may be more than one correct choice.)

In many cartoon shows,a character runs off a cliff,realizes his predicament,and lets out a scream.He continues to scream as he falls.If the physical situation is portrayed correctly,from the vantage point of an observer at the foot of the cliff,the pitch of the scream as he falls should be