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A wave on a string is described by $$ y(x, t)=15.0 \sin (\pi x / 8-4 \pi t), $$ where \(x\) and \(y\) are in centimeters and \(t\) is in seconds. (a) What is the transverse speed for a point on the string at \(x=6.00 \mathrm{~cm}\) when \(t=0.250 \mathrm{~s}\) ? (b) What is the maximum transverse speed of any point on the string? (c) What is the magnitude of the transverse acceleration for a point on the string at \(x=6.00 \mathrm{~cm}\) when \(t=0.250 \mathrm{~s}\) ? (d) What is the magnitude of the maximum transverse acceleration for any point on the string?

Short Answer

Expert verified
(a) -133.97 cm/s, (b) 188.5 cm/s, (c) -1668.06 cm/s², (d) 2363.01 cm/s².

Step by step solution

01

Locate the wave function and differentiate to find velocity

The wave function is given as \(y(x, t)=15.0 \sin (\pi x / 8-4 \pi t)\). To find the transverse velocity of a point on the string, we need to differentiate this wave function with respect to time \(t\):\[ v(x, t) = \frac{\partial y}{\partial t} = 15.0 \cdot (-4\pi) \cos(\pi x / 8 - 4\pi t) \]\[ v(x, t) = -60\pi \cos(\pi x / 8 - 4\pi t) \]
02

Calculate transverse speed at x = 6.00 cm, t = 0.250 s

Substitute \(x = 6.00\, \mathrm{cm}\) and \(t = 0.250\, \mathrm{s}\) into the transverse velocity expression:\[ v(6, 0.250) = -60\pi \cos\left(\frac{\pi \cdot 6}{8} - 4\pi \cdot 0.250\right) \]Calculate inside the cosine:\[ \frac{\pi \cdot 6}{8} - 4\pi \cdot 0.250 = \frac{3\pi}{4} - \pi = -\frac{\pi}{4}\]Determine \(\cos\left(-\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}\), hence:\[ v(6, 0.250) = -60 \pi \left(\frac{\sqrt{2}}{2}\right) = -30\pi\sqrt{2} \approx -133.97\, \mathrm{cm/s}\]
03

Determine maximum transverse speed

The maximum transverse speed occurs when \(\cos(\pi x / 8 - 4\pi t) = \pm 1\). The maximum value of the cosine function is 1, hence:\[ v_{\text{max}} = |60\pi \cdot 1| = 60\pi \approx 188.5 \mathrm{\, cm/s}\]
04

Find expression for transverse acceleration

To find the transverse acceleration, differentiate the velocity function \(v(x, t)\) with respect to time \(t\):\[ a(x, t) = \frac{\partial v}{\partial t} = 60\pi \cdot 4\pi \sin(\pi x / 8 - 4\pi t) \]\[ a(x, t) = 240\pi^2 \sin(\pi x / 8 - 4\pi t) \]
05

Calculate transverse acceleration at x = 6.00 cm, t = 0.250 s

Substitute \(x = 6.00\, \mathrm{cm}\) and \(t = 0.250\, \mathrm{s}\) into the transverse acceleration expression:\[ a(6, 0.250) = 240\pi^2 \sin\left(-\frac{\pi}{4}\right) \]Since \(\sin(-\frac{\pi}{4}) = -\frac{\sqrt{2}}{2}\), we have:\[ a(6, 0.250) = 240\pi^2 \left(-\frac{\sqrt{2}}{2}\right) = -120\pi^2\sqrt{2} \approx -1668.06\, \mathrm{cm/s^2}\]
06

Determine maximum transverse acceleration

The maximum transverse acceleration occurs when \(\sin(\pi x / 8 - 4\pi t) = \pm 1\). Hence, the maximum value of the sine function is 1:\[ a_{\text{max}} = |240\pi^2| = 240\pi^2 \approx 2363.01 \mathrm{\, cm/s^2} \]

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Key Concepts

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

Transverse Speed
Transverse speed in wave mechanics refers to how fast a point on a wave moves vertically as the wave passes. For this exercise, we are looking at a wave modeled as a function of both space (x) and time (t): \[ y(x, t) = 15.0 \sin \left(\frac{\pi x}{8} - 4\pi t\right) \] To find how this wave moves over time, we need to understand the term "transverse velocity", which is essentially the derivative of the wave function with respect to time. By differentiating the wave function, we find it to be: \[ v(x, t) = -60\pi \cos \left(\frac{\pi x}{8} - 4\pi t \right) \] This expression shows how the wave's height changes over time at various points along the wave. The negative sign indicates the direction of motion but doesn't affect the speed. Calculating at a specific point, like at \(x = 6.00\, \mathrm{cm}\) and \(t = 0.250\, \mathrm{s}\), will give us the instantaneous speed at that moment.
Transverse Acceleration
Transverse acceleration involves how rapidly the transverse speed is changing. When a point on a wave has a high acceleration value, it means its speed is changing quickly. We find transverse acceleration by differentiating the transverse velocity (which was derived from our wave function) with respect to time again. This gives us the expression: \[ a(x, t) = 240\pi^2 \sin \left(\frac{\pi x}{8} - 4\pi t \right) \] This shows how the velocity of the wave changes over time. Evaluating this at particular points like \(x = 6.00\, \mathrm{cm}\) and \(t = 0.250\, \mathrm{s}\) provides the acceleration of the point on the wave at that specific time. The wave's sine function guides us to understand how these changes are periodic and why they vary over time and position.
Differentiation of Wave Function
Differentiation is a mathematical process that helps us understand how changes happen in physical phenomena, like waves. For wave functions, differentiating with respect to time gives us insights about speed and acceleration. By taking the derivative of the wave function \[ y(x, t) = 15.0 \sin \left(\frac{\pi x}{8} - 4\pi t\right) \] with respect to time, we make sense of how the wave's shape changes over time. This derivative leads us to find the transverse speed \(v(x, t)\), which is crucial to understand how quickly a point on the wave moves. Differentiating once more provides transverse acceleration \(a(x, t)\), offering a deeper understanding of the wave's dynamics. Differentiation in this context evolves a simple wave function into a full picture of motion.
Sinusoidal Wave
A sinusoidal wave is a mathematical curve that describes smooth periodic oscillations. It is commonly modeled using sine or cosine functions, beautiful and symmetric cycles. The given wave function \[ y(x, t) = 15.0 \sin \left(\frac{\pi x}{8} - 4\pi t\right) \] is a sinusoidal wave. This type of wave is important in physics because it represents idealized, continuous wave patterns like sound and light waves. The sinusoidal wave is driven by trigonometric sine functions, which means it regularly repeats itself, creating uniform wave peaks and troughs. That periodicity and regularity make understanding wave motion and its effects more predictable.
Maximum Values in Trigonometry
Maximum values in trigonometry, especially in sinusoidal wave analysis, are vital in finding peak speeds and accelerations. The wave and its derivatives contain trigonometric functions such as sine and cosine, which inherently possess maximum and minimum values. The maximum of \cos(x)\ and \sin(x)\ is 1, and their minimum is -1. These values help determine: - The maximum transverse speed when \(\cos\) achieves \( \pm 1\) results in the largest possible value \(|60\pi|\). - Similarly, the maximum transverse acceleration arises when \(\sin\) is \(\pm 1\), leading to \(|240\pi^2|\) for peak acceleration. When analyzing wave motion, knowing these trigonometric values allows us to identify when the wave’s displacement, speed, and acceleration are at their peak. Recognizing these maxima is key to understanding the extreme behavior of waves.

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Most popular questions from this chapter

String \(A\) is stretched between two clamps separated by distance \(L\). String \(B\), with the same linear density and under the same tension as string \(A\), is stretched between two clamps separated by distance \(4 L\). Consider the first eight harmonics of string \(B\). For which of these eight harmonics of \(B\) (if any) does the frequency match the frequency of (a) \(A\) 's first harmonic, (b) \(A\) 's second harmonic, and (c) \(A\) 's third harmonic?

A rope, under a tension of \(200 \mathrm{~N}\) and fixed at both ends, oscillates in a second-harmonic standing wave pattern. The displacement of the rope is given by $$ y=(0.10 \mathrm{~m})(\sin \pi x / 2) \sin 12 \pi t $$ where \(x=0\) at one end of the rope, \(x\) is in meters, and \(t\) is in seconds. What are (a) the length of the rope, (b) the speed of the waves on the rope, and (c) the mass of the rope? (d) If the rope oscillates in a third-harmonic standing wave pattern, what will be the period of oscillation?

The following two waves are sent in opposite directions on a horizontal string so as to create a standing wave in a vertical plane: $$ \begin{aligned} &y_{1}(x, t)=(6.00 \mathrm{~mm}) \sin (4.00 \pi x-400 \pi t) \\ &y_{2}(x, t)=(6.00 \mathrm{~mm}) \sin (4.00 \pi x+400 \pi t) \end{aligned} $$ with \(x\) in meters and \(t\) in seconds. An antinode is located at point \(A\). In the time interval that point takes to move from maximum upward displacement to maximum downward displacement, how far does each wave move along the string?

The heaviest and lightest strings on a certain violin have linear densities of \(3.0\) and \(0.29 \mathrm{~g} / \mathrm{m}\). What is the ratio of the diameter of the heaviest string to that of the lightest string, assuming that the strings are of the same material?

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 \(39 \mathrm{~s}\), 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)?

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