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A sinusoidal wave of angular frequency 1200 rad/s and amplitude \(3.00 \mathrm{~mm}\) is sent along a cord with linear density \(2.00 \mathrm{~g} / \mathrm{m}\) 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) \(0.4 \pi\) rad, and (e) \(\pi\) rad?

Short Answer

Expert verified
(a) 16.8 W, (b) 33.6 W, (c) 67.2 W, (d) 63.3 W, (e) 0 W.

Step by step solution

01

Identify the Energy Transport Formula

The average power transported by a wave on a cord is given by the formula \[ P = \frac{1}{2} \mu \omega^2 A^2 v \]where \(P\) is the average power, \(\mu\) is the linear mass density of the cord, \(\omega\) is the angular frequency, \(A\) is the amplitude, and \(v\) is the wave speed. We'll calculate \(v\) in the next step.
02

Determine the Wave Speed

The wave speed \(v\) on a string is calculated using the formula \[ v = \sqrt{\frac{T}{\mu}} \]where \(T\) is the tension and \(\mu\) is the linear mass density. Given \(T = 1200 \text{ N}\) and \(\mu = 2.00 \, \text{g/m} = 0.002 \, \text{kg/m}\),you find \[ v = \sqrt{\frac{1200}{0.002}} = 774.6 \, \text{m/s}. \]
03

Calculate Power for a Single Wave

Using the wave speed calculated, determine the power transported by a single wave:\[ P = \frac{1}{2} (0.002) (1200)^2 (0.003)^2 (774.6) \]This yields:\[ P = \frac{1}{2} \times 0.002 \times 1440000 \times 9 \times 10^{-6} \times 774.6 = 16.8 \, \text{W}. \]
04

Calculate Total Power for Two Identical Waves on Separate Cords

If an identical wave travels along an adjacent, identical cord, the total power is simply the sum of the power from both waves. Thus:\[ P_{\text{total}} = 16.8 \, \text{W} + 16.8 \, \text{W} = 33.6 \, \text{W}. \]
05

Calculate Total Power for Two Waves on the Same Cord with Phase Difference 0

When two identical waves travel on the same cord with zero phase difference, their amplitudes add constructively. Amplitude becomes \(2A = 6.00 \, \text{mm}\). Calculate power using the new amplitude:\[ P = \frac{1}{2} \times 0.002 \times 1440000 \times (0.006)^2 \times 774.6 = 67.2 \, \text{W}. \]
06

Calculate Total Power for Two Waves on the Same Cord with Phase Difference 0.4Ï€

When waves are out of phase, their resultant amplitude \(A'\) is given by\[ A' = 2A \cos \left(\frac{\phi}{2}\right) \]For \(\phi = 0.4\pi\),\[ A' = 6.00 \, \text{mm} \times \cos \left(\frac{0.4\pi}{2}\right) = 5.68 \, \text{mm}. \] Thus power is:\[ P = \frac{1}{2} \times 0.002 \times 1440000 \times (0.00568)^2 \times 774.6 \approx 63.3 \, \text{W}. \]
07

Calculate Total Power for Two Waves on the Same Cord with Phase Difference π

For a phase difference of \(\pi\), the waves completely cancel, resulting in an amplitude of zero. Thus, the total power becomes:\[ P = 0 \, \text{W}. \]

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Key Concepts

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

Sinusoidal Wave
A sinusoidal wave is a type of wave characterized by its smooth and periodic oscillations, similar in form to a sine curve. This type of wave is crucial in understanding mechanical vibrations, electrical signals, and much more. Sinusoidal waves are defined by several key parameters:
  • Amplitude (A): The maximum height of the wave from its mean position. In this exercise, the amplitude is given as 3.00 mm.
  • Wavelength (\( \lambda \)): The distance between two corresponding points on the wave, such as crest to crest or trough to trough.
  • Frequency (\( f \)): The number of complete oscillations or cycles the wave undergoes per second.
  • Phase (\( \phi \)): Describes the starting point of the wave cycle. It can lead to wave interference when waves meet.
  • Wave Speed (\( v \)): The speed at which the wave propagates through the medium.
The given sinusoidal wave has a specific angular frequency and amplitude that help determine the energy transfer through the cord.
Understanding these wave properties allows for calculations involving wave interference, energy transport, and wave speed.
Linear Mass Density
Linear mass density, denoted as \( \mu \), is a measure of mass per unit length of an object. In wave mechanics, it plays a crucial role in determining how waves propagate through a medium, particularly in strings or cords. The unit of linear mass density is typically kg/m or g/m, and it is calculated as follows:
\[ \mu = \frac{m}{L} \]
where \( m \) is the total mass and \( L \) is the total length. In the context of the problem, the cord's linear mass density is given as 2.00 g/m, which converts to 0.002 kg/m for use in calculations.
A high linear mass density implies a higher concentration of mass in the medium, affecting wave speed. This is observed in the speed calculation formula:
\[ v = \sqrt{\frac{T}{\mu}} \]
where \( T \) is the tension in the cord. Understanding linear mass density is vital for accurately assessing how energy is transported by waves along a medium.
Wave Interference
Wave interference occurs when two or more waves meet while traveling through the same medium. The interaction can lead to constructive interference, where waves add up to produce a larger amplitude, or destructive interference, where they cancel each other out. This principle is key when considering how waves transport energy:
- **Constructive Interference:** When two waves in phase (phase difference of 0) overlap, their amplitudes add. If two identical waves collide in phase, the resulting amplitude is twice that of a single wave, leading to a significant increase in transported energy.
- **Destructive Interference:** If the phase difference is \( \pi \) radians, the waves completely cancel out, resulting in no net amplitude and zero energy transport.
When the phase difference is somewhere between 0 and \( \pi \), partial interference occurs. For example, with a 0.4e radians phase difference, resultant amplitudes are calculated using:
\[ A' = 2A \cos \left(\frac{\phi}{2}\right) \]
This formula reflects how phase differences modify the effective wave amplitude and thereby influence the energy transferred along a medium.
Angular Frequency
Angular frequency, commonly denoted as \( \omega \), relates to how fast a wave oscillates in terms of radians per second. It is a crucial property in characterizing sinusoidal waves and is defined by the relationship:
\[ \omega = 2\pi f \]
where \( f \) is the ordinary frequency measured in hertz (Hz). Angular frequency helps in describing the dynamic qualities of a wave in rotational terms, often used in physics and engineering.
In wave problems, angular frequency is tied to the energy transport capability of the wave. The power carried by a wave depends heavily on the angular frequency, as shown in the power transport formula:
\[ P = \frac{1}{2} \mu \omega^2 A^2 v \]
This equation shows how squared angular frequency times the amplitude and wave speed yields wave power. Thus, a higher angular frequency enhances the amount of energy a wave can transport, given the other factors remain constant.

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