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The equation of a transverse wave on a string is $$ y=(2.0 \mathrm{~mm}) \sin \left[\left(15 \mathrm{~m}^{-1}\right) x-\left(900 \mathrm{~s}^{-1}\right) t\right] . $$ The linear density is \(4.17 \mathrm{~g} / \mathrm{m}\). (a) What is the wave speed? (b) What is the tension in the string?

Short Answer

Expert verified
(a) The wave speed is 60 m/s. (b) The tension in the string is 15 N.

Step by step solution

01

Identify the Wave-Speed Expression

The equation of a wave is given by \( y = A \sin(kx - \omega t) \), where \( A \) is the amplitude, \( k \) is the wave number, and \( \omega \) is the angular frequency. From the wave equation \( y=(2.0 \, \text{mm}) \sin[(15 \, \text{m}^{-1}) x - (900 \, \text{s}^{-1}) t ] \), \( k = 15 \, \text{m}^{-1} \) and \( \omega = 900 \, \text{s}^{-1} \). The wave speed \( v \) is given by the relationship \( v = \frac{\omega}{k} \).
02

Calculate the Wave Speed

Substitute the values of \( \omega \) and \( k \) into the wave speed formula: \[v = \frac{\omega}{k} = \frac{900 \, \text{s}^{-1}}{15 \, \text{m}^{-1}} = 60 \, \text{m/s}.\]
03

Relate Wave Speed to Tension and Linear Density

The tension \( T \) in the string can be found using the formula for wave speed \( v = \sqrt{\frac{T}{\mu}} \), where \( \mu \) is the linear density of the string. Rearrange this formula to solve for tension: \[T = \mu v^2.\]
04

Convert Linear Density to Standard Units

The given linear density is \( 4.17 \, \text{g/m} \), which needs to be converted to \( \text{kg/m} \) for consistency with the SI units. Thus, \( 4.17 \, \text{g/m} \) = 0.00417 \, \text{kg/m}.
05

Calculate the Tension in the String

Substitute the values of \( \mu = 0.00417 \, \text{kg/m} \) and \( v = 60 \, \text{m/s} \) into the tension formula: \[T = 0.00417 \, \text{kg/m} \times (60 \, \text{m/s})^2 = 15 \, \text{N}.\]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Transverse Wave
A transverse wave is a type of wave where the medium's displacement is perpendicular to the direction of the wave's travel. Imagine a wave moving through a string – as the wave moves horizontally, the particles of the string move up and down, creating crests and troughs.
This type of motion is characteristic of waves on strings, water surfaces, and electromagnetic waves like light. Transverse waves can reflect or change direction, and when they encounter obstacles, they may also create interference patterns if other waves are present.
  • The amplitude of a transverse wave reflects how "tall" or "deep" the waves are, which corresponds to the wave's energy. Higher amplitude means more energy.
  • The wavelength is the distance between two consecutive crests or troughs.
  • The frequency tells us how many wave crests pass a given point per second.
When dealing with calculations involving transverse waves, the wave function, such as in the given equation, gives insights into these properties through parameters like amplitude, wave number, and angular frequency.
Wave Speed
Wave speed is how fast the wave travels through the medium. It's a crucial concept in understanding waves, as it ties together frequency and wavelength using the formula: \[ v = \frac{\omega}{k} \] where \( v \) is the wave speed, \( \omega \) is the angular frequency, and \( k \) is the wave number.
In our example, using the wave equation \( y=(2.0 \text{ mm}) \sin[(15 \text{ m}^{-1})\- (900 \text{ s}^{-1}) t ] \), we have found that the wave speed \( v = 60 \text{ m/s} \).
  • The angular frequency \( \omega \) is how fast the wave oscillates in radians per second.
  • The wave number \( k \) is related to the wavelength \( \lambda \) by the relationship \( k = \frac{2\pi}{\lambda} \).
Understanding wave speed allows us to predict how waves propagate through different media, vital for applications like sound transmission, communication technologies, and physical simulations.
Linear Density
Linear density \( \mu \) is defined as the mass per unit length of a string or medium through which a wave moves. It plays a pivotal role in determining the wave speed and the tension in the string.
Mathematically, it is expressed as \( \mu = \frac{m}{l} \), where \( m \) is mass and \( l \) is length. In the given problem, the linear density is provided as \( 4.17 \text{ g/m} \), which converts to \( 0.00417 \text{ kg/m} \) for consistency with standard SI units.
  • A higher linear density implies more mass per meter of string, affecting how a wave propagates through the medium.
  • Linear density is an inherent property of the string or medium, independent of wave characteristics.
This conversion and its understanding are crucial in calculations involving wave equations, especially when finding other properties, like tension.
Tension in String
Tension in a string is the force exerted along the string's length, which impacts how waves travel through the string. It's closely linked to wave speed and linear density according to the formula for wave speed \( v = \sqrt{\frac{T}{\mu}} \), rearranged to solve for tension as \( T = \mu v^2 \).
In this exercise, with the corrected linear density of \( 0.00417 \text{ kg/m} \) and calculated wave speed of \( 60 \text{ m/s} \), tension in the string comes out to be \( 15 \text{ N} \).
  • The tension directly affects how fast the wave travels; more tension results in a higher wave speed.
  • Understanding tension is essential for tuning musical instruments, designing materials, and engineering applications where wave propagation through strings is relevant.
Correctly accounting for both tension and linear density ensures precise predictions of wave behavior, which is necessary for both theoretical and practical applications.

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Most popular questions from this chapter

A human wave. During sporting events within large, densely packed stadiums, spectators will send a wave (or pulse) around the stadium (Fig. 16-29). As the wave reaches a group of spectators, they stand with a cheer and then sit. At any instant, the width \(w\) of the wave is the distance from the leading edge (people are just about to stand) to the trailing edge (people have just sat down). Suppose a human wave travels a distance of 853 seats around a stadium in \(51 \mathrm{~s}\), with spectators requiring about \(1.8 \mathrm{~s}\) to respond to the wave's passage by standing and then sitting. What are (a) the wave speed \(v\) (in seats per second) and (b) width \(w\) (in number of seats)?

A sinusoidal wave of angular frequency \(1200 \mathrm{rad} / \mathrm{s}\) and amplitude \(3.00 \mathrm{~mm}\) is sent along a cord with linear density \(4.00 \mathrm{~g} / \mathrm{m}\) and tension \(1200 \mathrm{~N}\). (a) What is the average rate at which energy is transported by the wave to the opposite end of the cord? (b) If, simultaneously, an identical wave travels along an adjacent, identical cord, what is the total average rate at which energy is transported to the opposite ends of the two cords by the waves? If, instead, those two waves are sent along the same cord simultaneously, what is the total average rate at which they transport energy when their phase difference is (c) 0 , (d) \(0.4 \pi \mathrm{rad}\), and (e) \(\pi \mathrm{rad}\) ?

A sinusoidal wave is traveling on a string with speed \(40 \mathrm{~cm} / \mathrm{s}\). The displacement of the particles of the string at \(x=10 \mathrm{~cm}\) varies with time according to \(y=(4.0 \mathrm{~cm}) \sin \left[5.0-\left(4.0 \mathrm{~s}^{-1}\right) t\right]\). The linear density of the string is \(4.0 \mathrm{~g} / \mathrm{cm}\). What are (a) the frequency and (b) the wavelength of the wave? If the wave equation is of the form \(y(x, t)=y_{m} \sin (k x \pm \omega t)\), what are (c) \(y_{m}\), (d) \(k\), (e) \(\omega\), and (f) the correct choice of sign in front of \(\omega ?(g)\) What is the tension in the string?

A \(100 \mathrm{~g}\) wire is held under a tension of \(220 \mathrm{~N}\) with one end at \(x=0\) and the other at \(x=10.0 \mathrm{~m}\). At time \(t=0\), pulse 1 is sent along the wire from the end at \(x=10.0 \mathrm{~m}\). At time \(t=30.0 \mathrm{~ms}\), pulse 2 is sent along the wire from the end at \(x=0 .\) At what position \(x\) do the pulses begin to meet?

Two identical traveling waves, moving in the same direction, are out of phase by \(0.70 \pi \mathrm{rad}\). What is the amplitude of the resultant wave in terms of the common amplitude \(y_{m}\) of the two combining waves?

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