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A harmonic wave travels along a string. (a) At a point where the displacement of the string is greatest, is the kinetic energy of the string a maximum or a minimum? Explain. (b) At a point where the displacement of the string is zero, is the kinetic energy of the string a maximum or a minimum? Explain.

Short Answer

Expert verified
(a) Minimum; (b) Maximum.

Step by step solution

01

Understanding the Relationship Between Displacement and Kinetic Energy

To determine the kinetic energy of the string at different points of displacement, we first need to understand that the maximum displacement corresponds to maximum potential energy (as kinetic energy and potential energy are inversely related in a harmonic motion). When the displacement is at a maximum, the string momentarily stops before changing direction, resulting in zero velocity and hence, minimum kinetic energy.
02

Evaluating Kinetic Energy at Maximum Displacement

At the point of maximum displacement, the particle on the string is at its peak position along the wave (amplitude), leading to zero velocity at that instant. According to the kinetic energy formula: \[ KE = \frac{1}{2}mv^2 \]where \(v\) is the velocity, if \(v = 0\), then \(KE = 0\). Thus, at maximum displacement, the kinetic energy is a minimum.
03

Analyzing Kinetic Energy at Zero Displacement

At the zero displacement point, which is the equilibrium position, the displacement from the mean position is zero. Here, the string passes through its equilibrium position at maximum speed since there is no change in potential energy. This implies that the kinetic energy, given by the same formula: \[ KE = \frac{1}{2}mv^2 \]is at its maximum because the velocity \(v\) is greatest.
04

Conclusion Based on Energy Conservation Principles

Summarizing the observations: at maximum displacement, potential energy is maximum and kinetic energy is minimum since the velocity is zero. At zero displacement, kinetic energy is maximum due to maximum velocity and minimum potential energy.

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Key Concepts

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

Kinetic Energy
Kinetic energy in physics refers to the energy an object possesses due to its motion. In the context of a harmonic wave, it is crucial to understand how kinetic energy varies as the wave moves. The amount of kinetic energy can be calculated by the formula:
  • \( KE = \frac{1}{2}mv^2 \)
where \(m\) is the mass of the object and \(v\) is its velocity.

In a harmonic wave traveling along a string, kinetic energy plays a key role in describing the motion. At any point where the string has the greatest displacement, the velocity is momentarily zero as it changes direction. This is where kinetic energy reaches its minimum. Conversely, at points where the displacement is zero, the string moves fastest, resulting in maximum kinetic energy.

Understanding these points helps in grasping how energy is transferred and conserved in harmonic motions.
Potential Energy
Potential energy is another form of energy that is especially important in harmonic motion. It is the energy stored due to an object's position or configuration. In a harmonic wave traveling along a string, potential energy reaches its maximum value at points of greatest displacement, which are the peaks or troughs of a wave.

At maximum displacement, the wave holds maximum potential energy because the string is stretched or compressed the most and ready to release energy as it returns to its equilibrium position. When the string is at zero displacement, the potential energy is at its minimum. This is due to the object being at its natural resting position, where no energy is stored for further motion outside the equilibrium location.

Ultimately, potential and kinetic energy are inversely related during harmonic motion, constantly exchanging forms as the wave progresses.
Wave Displacement
Wave displacement is the term used to describe how far a point on the wave has moved from its equilibrium position. It's an essential measure in understanding harmonic waves, indicating how much energy is stored or released.

In a harmonic wave, displacement reaches its peak at the topmost point of a crest or at the bottom of a trough. These are the points where the string experiences the maximum force trying to pull it back to its equilibrium position. As the displacement increases, the potential energy increases, and the kinetic energy decreases because the object momentarily stops before reversing direction.

Displacement is key in assessing the behavior and energy distribution in waves, allowing for a deeper understanding of how mechanical energy manifests itself in waveforms.
Energy Conservation
The principle of energy conservation states that energy cannot be created or destroyed; it can only change forms. In the context of harmonic motion, this principle is evident in how kinetic and potential energy trade places throughout the motion.

At maximum displacement, all the system's energy is stored as potential energy. As the wave moves through its equilibrium position, this energy converts into kinetic energy, reaching its peak when displacement drops to zero. This conversion is a smooth transition observed in a continuous cycle.

The conservation of energy in harmonic waves explains how energy is efficiently transferred through the medium without any loss, highlighting the elegant and predictable nature of physical laws governing motion.
Harmonic Wave
Harmonic waves are a type of wave where particles of the medium oscillate in a regular and repeating fashion. They can be visualized as sine waves, characterized by consistent amplitude, frequency, and wavelength.

In a string, a harmonic wave manifests as vibrations that transfer energy along the length of the string without causing permanent displacement of the medium. These waves demonstrate both kinetic and potential energy forms. As they travel, energy shifts seamlessly between these types. This conservation and oscillation of energy are what make harmonic waves particularly interesting and useful in various applications, from musical instruments to understanding sound and light.

Grasping the behavior of harmonic waves is fundamental for students seeking to explore deeper into wave dynamics and the broader field of physics.

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Most popular questions from this chapter

Shallow-Water Waves In shallow water of depth \(d\) the speed of waves is approximately \(v=\sqrt{g d}\). Find the speed and frequency of a wave with wavelength \(0.75 \mathrm{cm}\) in water that is \(2.6 \mathrm{cm}\) deep.

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