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Two waves are traveling in opposite directions on the same string. The displacements caused by the individual waves are given by \(y_{1}=(24.0 mm) \sin (9.00 \pi t-1.25 \pi x)\) and \(y_{2}=(35.0 mm) \sin (2.88 \pi t+ 0.400 \pi x\) ). Note that the phase angles \((9.00 \pi t-1.25 \pi x)\) and \((2.88 \pi t+0.400 \pi x)\) are in radian, \(t\) is in seconds, and \(x\) is in meters. At \(t=4.00 s,\) what is the net displacement (in \(mm )\) of the string at (a) \(x=2.16 m\) and \((b) x=2.56 m ?\) Be sure to include the algebraic \(\operatorname{sign}(+or-)\) with your answers.

Short Answer

Expert verified
For (a) \(x = 2.16 \text{ m}\), the net displacement is \(-19.710 \text{ mm}\). For (b) \(x = 2.56 \text{ m}\), the net displacement is \(39.844 \text{ mm}\).

Step by step solution

01

Identify the Wave Equations and Variables

The displacements of the waves are given by \(y_1 = (24.0 \text{ mm}) \sin(9.00 \pi t - 1.25 \pi x)\) and \(y_2 = (35.0 \text{ mm}) \sin(2.88 \pi t + 0.400 \pi x)\). We need to find the net displacement \(y_{net} = y_1 + y_2\) for \(t = 4.00\) seconds at \(x = 2.16\) meters and \(x = 2.56\) meters.
02

Calculate y1 for x = 2.16 m, t = 4.00 s

Substitute \(t = 4.00\) and \(x = 2.16\) into \(y_1 = 24.0 \sin(9.00 \pi t - 1.25 \pi x)\):\[y_1 = 24.0 \sin(9.00 \pi \times 4.00 - 1.25 \pi \times 2.16).\]This simplifies to \(y_1 = 24.0 \sin(36\pi - 2.7\pi) = 24.0 \sin(33.3\pi)\). Since \(\sin(n\pi) = 0\) where \(n\) is an integer, we find \(33.3\mod 2 = 1.3\), thus evaluate \(\sin(1.3\pi)\). Calculate \(\sin(1.3\pi)\) to find \(y_1 \approx -23.999 \text{ mm}\).
03

Calculate y2 for x = 2.16 m, t = 4.00 s

Substitute \(t = 4.00\) and \(x = 2.16\) into \(y_2 = 35.0 \sin(2.88 \pi t + 0.400 \pi x)\):\[y_2 = 35.0 \sin(2.88 \pi \times 4.00 + 0.400 \pi \times 2.16).\]This simplifies to \(y_2 = 35.0 \sin(11.52\pi + 0.864\pi) = 35.0 \sin(12.384\pi)\). Evaluate \(\sin(0.384\pi)\) to find \(y_2 \approx 4.289 \text{ mm}\).
04

Net Displacement for x = 2.16 m, t = 4.00 s

Add \(y_1\) and \(y_2\) to find the net displacement:\[y_{net} = -23.999 + 4.289 = -19.710 \text{ mm}.\]
05

Calculate y1 for x = 2.56 m, t = 4.00 s

Substitute \(t = 4.00\) and \(x = 2.56\) into \(y_1 = 24.0 \sin(9.00 \pi t - 1.25 \pi x)\):\[y_1 = 24.0 \sin(9.00 \pi \times 4.00 - 1.25 \pi \times 2.56).\]This simplifies to \(y_1 = 24.0 \sin(36\pi - 3.2\pi) = 24.0 \sin(32.8\pi)\). Evaluate \(\sin(0.8\pi)\) to find \(y_1 \approx 24.0 \text{ mm}\).
06

Calculate y2 for x = 2.56 m, t = 4.00 s

Substitute \(t = 4.00\) and \(x = 2.56\) into \(y_2 = 35.0 \sin(2.88 \pi t + 0.400 \pi x)\):\[y_2 = 35.0 \sin(2.88 \pi \times 4.00 + 0.400 \pi \times 2.56).\]This simplifies to \(y_2 = 35.0 \sin(11.52\pi + 1.024\pi) = 35.0 \sin(12.544\pi)\). Evaluate \(\sin(0.544\pi)\) to find \(y_2 \approx 15.844 \text{ mm}\).
07

Net Displacement for x = 2.56 m, t = 4.00 s

Add \(y_1\) and \(y_2\) to find the net displacement:\[y_{net} = 24.0 + 15.844 = 39.844 \text{ mm}.\]

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Key Concepts

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

Wave Equation
The wave equation is the cornerstone of understanding how waves behave as they travel through different mediums. It is a mathematical representation of wave propagation which describes the motion and amplitude of a wave at any given point and time. In this scenario, two wave equations are given:
  • Wave 1: \( y_1 = (24.0 \, \text{mm}) \sin(9.00 \pi t - 1.25 \pi x) \)
  • Wave 2: \( y_2 = (35.0 \, \text{mm}) \sin(2.88 \pi t + 0.400 \pi x) \)
Both equations include sine functions, which are characteristic for waves, and expressions involving \( \pi \), \( t \), and \( x \), indicating that they are affected by both time (\( t \)) and position (\( x \)). The coefficients beside \( t \) and \( x \) determine the wave's speed and wave number respectively.
Wave equations help in calculating the displacement of waves at any point by substituting appropriate \( t \) and \( x \) values, as demonstrated in the problem solution provided. Understanding these parameters is crucial in solving problems related to wave behavior.
Net Displacement
Net displacement refers to the total shift or movement of a string or medium at a particular point and time due to multiple waves traveling through it. When two or more waves meet, they combine their effects and create interference, which affects the net displacement.
To find the net displacement at any point where two waves intersect, we add the displacements caused by each individual wave. Mathematically, it is expressed as:
  • \( y_{\text{net}} = y_1 + y_2 \)
In our exercise, at the specific times and positions given, the net displacement was calculated by substituting the position \( x \) and time \( t \) values into the wave equations, calculating each wave displacement \( y_1 \) and \( y_2 \), and then adding them together.
The result indicates how much the specific point on the string has moved from its equilibrium position, revealing the outcome of wave interference at that location. This concept is pivotal in understanding phenomena such as constructive and destructive interference in wave mechanics.
Sinusoidal Waves
Sinusoidal waves are a fundamental type of periodic wave, characterized by a wave pattern that can be described by the sine or cosine function. Such waves are crucial in explaining various natural phenomena including sound and light waves.
In this exercise, both given waves are sinusoidal due to the presence of the sine function in their equations:
  • \( y_1 = (24.0 \, \text{mm}) \sin(9.00 \pi t - 1.25 \pi x) \)
  • \( y_2 = (35.0 \, \text{mm}) \sin(2.88 \pi t + 0.400 \pi x) \)
Each signal repeats its pattern over a specific interval, and the function's amplitude indicates the wave’s maximum displacement. The arguments of the sine functions, involving phase angles with \( \pi \), determine the frequency and direction of the wave.
Sinusoidal waves are essential in analyzing simple harmonic motion because the solutions of the wave equation involve these types of functions. Their predictability and smooth oscillations make them ideal models for a wide range of physical systems and technological applications.

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