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A transverse wave on a rope is given by $$ y(x, t)=(0.750 \mathrm{cm}) \cos \pi\left[\left(0.400 \mathrm{cm}^{-1}\right) x+\left(250 \mathrm{s}^{-1}\right) t\right] $$ (a) Find the amplitude, period, frequency, wavelength, and speed of propagation. (b) Sketch the shape of the rope at these values of t: \(0,0.0005\) s, 0.0010 s. (c) Is the wave traveling in the \(+x-\) or \(-x\) -direction? (d) The mass per unit length of the rope is \(0.0500 \mathrm{kg} / \mathrm{m} .\) Find the tension. (e) Find the average power of this wave.

Short Answer

Expert verified
Amplitude: 0.750 cm; Wavelength: 5 cm; Frequency: 125 Hz; Speed: 6.25 m/s; Direction: +x; Tension: 1.95 N; Avg. Power: 17.3 W.

Step by step solution

01

Identify the Wave Equation Components

The equation for the wave is given by: \[ y(x, t) = (0.750 \text{ cm}) \cos \pi \left[ (0.400 \text{ cm}^{-1}) x + (250 \text{ s}^{-1}) t \right] \] The general form of a wave equation is \( y(x, t) = A \cos(kx + \omega t + \phi) \). By comparing, we can identify: Amplitude \( A = 0.750 \text{ cm} \), Wave number \( k = 0.400 \pi \text{ cm}^{-1} \), Angular frequency \( \omega = 250 \pi \text{ s}^{-1} \).
02

Calculate the Amplitude

The amplitude of the wave is the maximum displacement from the rest position. From the wave equation, the amplitude \( A = 0.750 \text{ cm} \).
03

Calculate the Wavelength

The wavelength \( \lambda \) can be found using the relationship \( \lambda = \frac{2\pi}{k} \). Given \( k = 0.400\pi \text{ cm}^{-1} \), \[ \lambda = \frac{2\pi}{0.400\pi} \approx 5 \text{ cm} \].
04

Calculate the Frequency

The frequency \( f \) is related to the angular frequency by \( \omega = 2\pi f \). Solving for \( f \) gives us \( f = \frac{\omega}{2\pi} = \frac{250\pi}{2\pi} = 125 \text{ Hz} \).
05

Calculate the Period

The period \( T \) is the inverse of the frequency: \[ T = \frac{1}{f} = \frac{1}{125} \approx 0.008 \text{ s} \].
06

Calculate the Speed of Propagation

The speed \( v \) of the wave is given by \( v = f \cdot \lambda \). Thus, \[ v = 125 \times 5 = 625 \text{ cm/s} = 6.25 \text{ m/s} \].
07

Determine the Direction of Propagation

The sign of \( kx + \omega t \) term in the wave equation indicates the wave's direction. Since both are positive, the wave is traveling in the "+x" direction.
08

Sketch the Waveform at Given Times

At \( t = 0 \), \( t = 0.0005 \text{ s} \), and \( t = 0.0010 \text{ s} \), sketch the wave using the equation. Notice that the wave travels, so changes in \( t \) lead to shifts in the wave along the x-axis.
09

Calculate the Tension in the Rope

Using the formula \( v = \sqrt{\frac{T}{\mu}} \), where \( \mu = 0.0500 \text{ kg/m} \), solve for tension \( T \): \( 6.25 = \sqrt{\frac{T}{0.0500}} \). Then, \[ T = (6.25)^2 \times 0.0500 = 1.953125 \text{ N} \].
10

Calculate the Average Power

The average power is calculated using \( P_{avg} = \frac{1}{2} \mu A^2 \omega^2 v \). Substitute known values: \( \mu = 0.500 \text{ kg/m} \), \( A = 0.0075 \text{ m} \), \( \omega = 250\pi \text{ rad/s} \), and \( v = 6.25 \text{ m/s} \): \[ P_{avg} = \frac{1}{2} \times 0.0500 \times (0.0075)^2 \times (250\pi)^2 \times 6.25 \approx 17.3 \text{ W} \].

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Key Concepts

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

Transverse Waves
Transverse waves are a type of wave where the oscillations occur perpendicular to the direction of the wave's travel. Imagine a rope being flicked up and down; the motion of the rope is up and down, while the wave travels horizontally along the length of the rope.

Transverse waves can be seen in many scenarios including light waves and water ripples. In distinguishing them from longitudinal waves, like sound waves, transverse waves require a medium that supports shear stress, such as solids. This is part of the reason why transverse waves do not travel through gases or liquids effectively — they don't support the sideways shear that these waves create.

In our wave equation, the wave is transverse since it involves the displacement of the medium (the rope) perpendicular to the wave's direction.
Wavelength Calculation
The wavelength of a wave is a fundamental property and gives the distance over which the wave's shape repeats. It is represented by the symbol \( \lambda \) and is typically measured in meters or centimeters. Wavelength is inversely proportional to the wave number (k), according to the formula: \[\lambda = \frac{2\pi}{k} \]

In this specific wave equation, we have identified the wave number as \(0.400\pi \ \, \text{cm}^{-1} \). Therefore, substituting into the wavelength formula gives us: \[\lambda = \frac{2\pi}{0.400\pi} \approx 5 \, \text{cm} \]

This implies that every 5 cm along the rope, the wave pattern repeats itself, indicating the regular periodic property of the wave.
Wave Speed
Wave speed \( v \) is a crucial concept in understanding how fast a wave propagates through a medium. It is calculated by multiplying the frequency \( f \) by the wavelength \( \lambda \): \[v = f \times \lambda\]

In our example, the frequency was found to be 125 Hz, and the wavelength is 5 cm. This results in a wave speed of:
\[ v = 125 \, \text{Hz} \times 5 \, \text{cm} = 625 \, \text{cm/s} \]

Thus, the wave travels at a speed of 6.25 m/s along the rope. Wave speed aligns with how quickly energy and information are transmitted through the medium.
Wave Power
Wave power pertains to the rate at which energy is transferred by the wave. For mechanical waves like those on a rope, the average power \( P_{avg} \) can be calculated using: \[P_{avg} = \frac{1}{2} \mu A^2 \omega^2 v \]

Where:
  • \( \mu \) is the mass per unit length of the rope.
  • \( A \) is the amplitude of the wave in meters.
  • \( \omega \) is the angular frequency.
  • \( v \) is the wave speed.

In our specific example, substituting the values gives us: \
  • \( \mu = 0.0500 \, \text{kg/m}, \)
  • \( A = 0.0075 \, \text{m}, \)
  • \( \omega = 250\pi \, \text{rad/s}, \)
  • \( v = 6.25 \, \text{m/s} \)
\[ P_{avg} \approx 17.3 \, \text{W} \]

This calculation represents the energy transmitted by the wave per second, giving us insight into how much work can be done by the energy carried in the wave.

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Most popular questions from this chapter

A water wave traveling in a straight line on a lake is described by the equation $$ y(x, t)=(3.75 \mathrm{cm}) \cos \left(0.450 \mathrm{cm}^{-1} x+5.40 \mathrm{s}^{-1} t\right) $$ where \(y\) is the displacement perpendicular to the undisturbed surface of the lake. (a) How much time does it take for one complete wave pattern to go past a fisherman in a boat at anchor, and what horizontal distance does the wave crest travel in that time? (b) What are the wave number and the number of waves per second that pass the fisherman? (c) How fast does a wave crest travel past the fisherman, and what is the maximum speed of his cork floater as the wave causes it to bob up and down?

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