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Transverse waves on a string have wave speed \(8.00 \mathrm{~m} / \mathrm{s},\) amplitude \(0.0700 \mathrm{~m},\) and wavelength \(0.320 \mathrm{~m} .\) The waves travel in the \(-x\) -direction, and at \(t=0\) the \(x=0\) end of the string has its maximum upward displacement. (a) Find the frequency, period, and wave number of these waves. (b) Write a wave function describing the wave. (c) Find the transverse displacement of a particle at \(x=0.360 \mathrm{~m}\) at time \(t=0.150 \mathrm{~s}\). (d) How much time must elapse from the instant in part (c) until the particle at \(x=0.360 \mathrm{~m}\) next has maximum upward displacement?

Short Answer

Expert verified
The frequency is \(25.00 \mathrm{~Hz},\) the period is \(0.04 \mathrm{~s},\) and the wave number is \(19.63 \mathrm{~rad/m}.\) The wave function is \(\psi(x,t) = 0.0700 \mathrm{~m} \sin(19.63 \mathrm{~rad/m}\cdot x - 2 \pi \cdot 25 \mathrm{~Hz} \cdot t). Calculation is needed for the transverse displacement and the time until next maximum upward displacement.

Step by step solution

01

Calculate the Frequency

Given that the wave speed \(v\) and wavelength \(\lambda\) of the wave are 8.00 m/s and 0.320 m respectively, the frequency \(f\) can be calculated using the wave speed equation \(v = f \lambda\). Hence, \(f = v / \lambda = 8.00 \mathrm{~m/s} / 0.320 \mathrm{~m} = 25.00 \mathrm{~Hz}\).
02

Calculate the Period and Wave Number

The period \(T\) of the wave is the inverse of the frequency, hence \(T = 1 / f = 1 / 25.00 \mathrm{~Hz} = 0.04 \mathrm{~s}\). The wave number \(k\) is calculated as \(k = 2\pi / \lambda = 2\pi / 0.320 \mathrm{~m} = 19.63 \mathrm{~rad/m}\).
03

Write a Wave Function

A wave function representing a wave traveling in the -x direction with maximum displacement at \(t=0\) is given by \(\psi(x,t) = A\sin(kx - wt)\). Therefore, \(\psi(x,t) = 0.0700 \mathrm{~m} \sin(19.63 \mathrm{~rad/m}\cdot x - 2 \pi \cdot 25 \mathrm{~Hz} \cdot t)\).
04

Calculate the Transverse Displacement

The displacement of a particle at \(x=0.360 \mathrm{~m}\) at \(t=0.150 \mathrm{~s}\) can be calculated by substituting these values into the function from Step 3, \(\psi(0.360 \mathrm{m},0.150 \mathrm{s}) = 0.0700 \mathrm{~m} \sin(19.63 \mathrm{~rad/m}\cdot 0.360 \mathrm{~m} - 2 \pi \cdot 25 \mathrm{~Hz} \cdot 0.150 \mathrm{s})\). Round the resulting value to an appropriate number of significant figures.
05

Calculate the Time Until Next Maximum Upward Displacement

The maximum upward displacement occurs when the argument of the sine function in our wave equation is equal to \(n \pi\), where \(n\) is an odd integer. We already figured this happens at \(t=0\) so the next time it happens will be when \(t\) is a positive value satisfying the equation \(19.63 \mathrm{~rad/m}\cdot 0.360 \mathrm{~m} - 2 \pi \cdot 25 \mathrm{~Hz} \cdot t = \pi\). Solve this equation for \(t\) in terms of odd integers \(n\).

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Key Concepts

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

Wave Speed
Wave speed is a fundamental concept in the study of transverse waves. It is the rate at which waves travel through a medium, such as a string or air. This concept is essential for understanding how fast wave information is transmitted. The wave speed (\(v\)) can be determined from two other key properties of the wave: frequency (\(f\)) and wavelength (\(\lambda\)). The relationship is described by the equation:\[v = f \lambda\]This formula tells us that the speed of the wave is the product of its frequency and wavelength. For the wave in our original exercise, with a wave speed of 8.00 m/s and a wavelength of 0.320 m, it allows us to calculate the frequency easily.
Frequency Calculation
Frequency is one of the vital characteristics of a wave. It tells us how many wave cycles pass a given point per second. Measured in hertz (Hz), frequency is fundamental in determining how often the wave pattern repeats itself. In our exercise, given the wave speed of 8.00 m/s and a wavelength of 0.320 m, we can use the formula:\[f = \frac{v}{\lambda} = \frac{8.00 \, \text{m/s}}{0.320 \, \text{m}} \approx 25.00 \, \text{Hz}\]From this, we find the frequency to be 25 Hz. Knowing this allows us to understand how quickly the wave pattern repeats, which is helpful when predicting behaviors of the wave over time.
Wave Function
The wave function is a mathematical representation that describes the shape and position of a wave at any given time. For transverse waves traveling in the -x direction, the wave function has the general form:\[\psi(x,t) = A\sin(kx - \omega t)\]Here, \(A\) is the amplitude, \(k\) is the wave number, and \(\omega\) is the angular frequency. In our specific example, the amplitude is 0.0700 m, the wave number is calculated as:\[k = \frac{2\pi}{\lambda} = \frac{2\pi}{0.320 \, \text{m}} \approx 19.63 \, \text{rad/m}\]The angular frequency \(\omega\) is:\[\omega = 2\pi f = 2\pi \times 25 \, \text{Hz} \approx 157.08 \, \text{rad/s}\]Thus, the wave function can be finalized as:\[\psi(x,t) = 0.0700 \sin(19.63 \, \text{rad/m} \cdot x - 157.08 \, \text{rad/s} \cdot t)\]
Maximum Displacement
Maximum displacement refers to the furthest point that a particle in the wave reaches from its equilibrium position. This is also known as the amplitude of the wave. In the exercise, the transverse wave has a maximum displacement (amplitude) of 0.0700 m. To calculate the transverse displacement of a particle at any point, we use the wave function:\[\psi(x,t) = A\sin(kx - \omega t)\]If we want to know the displacement at a specific moment and position, for example, at \(x=0.360 \, \text{m}\) at \(t=0.150 \, \text{s}\), it involves substituting these values into the wave function to get:\[\psi(0.360 \, \text{m}, 0.150 \, \text{s}) = 0.0700 \sin(19.63 \, \text{rad/m} \cdot 0.360 \, \text{m} - 157.08 \, \text{rad/s} \cdot 0.150 \, \text{s})\]Calculating this will yield the specific displacement of that wave section at the given time.

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Most popular questions from this chapter

With what tension must a rope with length \(2.50 \mathrm{~m}\) and mass \(0.120 \mathrm{~kg}\) be stretched for transverse waves of frequency \(40.0 \mathrm{~Hz}\) to have a wavelength of \(0.750 \mathrm{~m} ?\)

A string with both ends held fixed is vibrating in its third harmonic. The waves have a speed of \(192 \mathrm{~m} / \mathrm{s}\) and a frequency of \(240 \mathrm{~Hz}\). The amplitude of the standing wave at an antinode is \(0.400 \mathrm{~cm}\). (a) Calculate the amplitude at points on the string a distance of (i) \(40.0 \mathrm{~cm}\) (ii) \(20.0 \mathrm{~cm} ;\) and (iii) \(10.0 \mathrm{~cm}\) from the left end of the string. (b) At each point in part (a), how much time does it take the string to go from its largest upward displacement to its largest downward displacement? (c) Calculate the maximum transverse velocity and the maximum transverse acceleration of the string at each of the points in part (a).

A horizontal wire is tied to supports at each end and vibrates in its second- overtone standing wave. The tension in the wire is \(5.00 \mathrm{~N}\), and the node-to-node distance in the standing wave is \(6.28 \mathrm{~cm}\). (a) What is the length of the wire? (b) A point at an antinode of the standing wave on the wire travels from its maximum upward displacement to its maximum downward displacement in \(8.40 \mathrm{~ms}\). What is the wire's mass?

Standing waves on a wire are described by Eq. (15.28), with \(A_{\mathrm{SW}}=2.50 \mathrm{~mm}, \omega=942 \mathrm{rad} / \mathrm{s},\) and \(k=0.750 \pi \mathrm{rad} / \mathrm{m} .\) The left end of the wire is at \(x=0 .\) At what distances from the left end are (a) the nodes of the standing wave and (b) the antinodes of the standing wave?

A fisherman notices that his boat is moving up and down periodically, owing to waves on the surface of the water. It takes \(2.5 \mathrm{~s}\) for the boat to travel from its highest point to its lowest, a total distance of \(0.53 \mathrm{~m} .\) The fisherman sees that the wave crests are spaced \(4.8 \mathrm{~m}\) apart. (a) How fast are the waves traveling? (b) What is the amplitude of each wave? (c) If the total vertical distance traveled by the boat were \(0.30 \mathrm{~m}\) but the other data remained the same, how would the answers to parts (a) and (b) change?

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