18. Waves & Sound

Intro to Waves

Introduction to Waves

Properties of Waves from Graphs

A fellow student with a mathematical bent tells you that the wave function of a traveling wave on a thin rope is y(x, t)=2.30mm cos[(16.98 rad/m^)x+(742 rad/s)t]. Being more practical, you measure the rope to have a length of 1.35 m and a mass of 0.00338 kg. You are then asked to determine the following: (f) tension in the rope; (g) average power transmitted by the wave.

Threshold of Pain. You are investigating the report of a UFO landing in an isolated portion of New Mexico, and you encounter a strange object that is radiating sound waves uniformly in all directions. Assume that the sound comes from a point source and that you can ignore reflections. You are slowly walking toward the source. When you are 7.5 m from it, you measure its intensity to be 0.11 W/m^2. An intensity of 1.0 W/m^2 is often used as the “threshold of pain.” How much closer to the source can you move before the sound intensity reaches this threshold?

Physics - Waves -  Introduction

Types of Waves

A jet plane at takeoff can produce sound of intensity 10.0 W/m^2 at 30.0 m away. But you prefer the tranquil sound of normal conversation, which is 1.0 μW/m^2. Assume that the plane behaves like a point source of sound. (a) What is the closest dis-tance you should live from the airport runway to preserve your peace of mind? (b) What intensity from the jet does your friend experience if she lives twice as far from the runway as you do? (c) What power of sound does the jet produce at takeoff?

What Is A Wave?

<p>A satellite captures images of a tsunami, and properties of the tsunami can be found from these images, providing important information to people who need to evacuate coastal areas. If satellite images of a tsunami show the distance from one peak to another is 500 km, and the period is 1 hour, how much time do people have to evacuate if the tsunami is found to be 100 km off shore?</p>

At a distance of 7.00x10^12 m from a star, the intensity of the radiation from the star is 15.4 W/m^2. Assuming that the star radiates uniformly in all directions, what is the total power output of the star?

Wave Basics

A horizontal string tied at both ends is vibrating in its fundamental mode. The traveling waves have speed v, frequency f, amplitude A, and wavelength λ. (a) Calculate the maximum transverse velocity and maximum transverse acceleration of points located at (i) x = λ/2, (ii) x = λ/4, and (iii) x = λ/8, from the left-hand end of the string.

One string of a certain musical instrument is 75.0 cm long and has a mass of 8.75 g. It is being played in a room where the speed of sound is 344 m/s. (a) To what tension must you adjust the string so that, when vibrating in its second overtone, it produces sound of wavelength 0.765 m? (Assume that the break-ing stress of the wire is very large and isn’t exceeded.) (b) What frequency sound does this string produce in its fundamental mode of vibration?

A 2.0-m-long string vibrates at its second-harmonic frequency with a maximum amplitude of 2.0 cm. One end of the string is at x=0 cm . Find the oscillation amplitude at x=10 , 20, 30, 40, and 50 cm.

A horizontal string tied at both ends is vibrating in its fundamental mode. The traveling waves have speed v, frequency f, amplitude A, and wavelength λ. (c) How much time does it take the string to go from its largest upward displacement to its largest downward displacement at the points located at (i) x = λ/2, (ii) x = λ/4, and (iii) x = λ/8, from the left-hand end of the string.

Distance Between Crests

 A string with a linear mass density of <math display=“inline”><mrow><mn>1</mn><mo>.</mo><mn>6</mn><mtext></mtext><mtext>&#x00A0;g/m</mtext></mrow></math> is under <math display=“inline”><mrow><mn>4</mn><mo>.</mo><mrow><mn>0</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">N</mi></mrow></mrow></math> of tension. How long would it take a wave pulse on this string to travel <math display=“inline”><mrow><mn>3</mn><mo>.</mo><mrow><mn>0</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">m</mi></mrow><mo>&#x003F;</mo></mrow></math> 

A horizontal string tied at both ends is vibrating in its fundamental mode. The traveling waves have speed v, frequency f, amplitude A, and wavelength λ. (b) What is the amplitude of the motion at the points located at (i) x = λ/2, (ii) x = λ/4, and (iii) x = λ/8, from the left-hand end of the string?

Wave Motion | Waves | Physics | FuseSchool

Energy Output. By measurement you determine that sound waves are spreading out equally in all directions from a point source and that the intensity is 0.026 W/m^2 at a distance of 4.3 m from the source. (a) What is the intensity at a distance of 3.1 m from the source?

Energy Output. By measurement you determine that sound waves are spreading out equally in all directions from a point source and that the intensity is 0.026 W/m^2 at a distance of 4.3 m from the source. (b) How much sound energy does the source emit in one hour if its power output remains constant?

The lowest note on a grand piano has a frequency of 27.5 Hz. The entire string is 2.00 m long and has a mass of 400 g. The vibrating section of the string is 1.90 m long. What tension is needed to tune this string properly?

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