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Questions tagged [potential-energy]

Potential energy is the energy of a body or a system due to the position of the body or the arrangement of the particles of the system.

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Why are there 6 interactions with 4 positive charges?

From a homework assignment, there are 4 spheres spaced 1cm apart. Each of the spheres are charged to +10nC and weigh 1 gram. The question wants us to find the final speed of the charges once they've ...
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Why energy is released (most of the time) when electrons are added to atomsg?

[Though initially the question may seem to belong to stack exchange chemistry but I believe that I would get a better physical explanation over here. ] Currently I was reading about electron ...
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Doubt in understanding the potential energy of dipole in external electric field?

When a dipole is placed in external electric field it experiences a torque $$\vec \tau = \vec p \ \times \vec E $$ whose magnitude is $$||\vec \tau|| = ||\vec p|| \cdot ||\vec E|| \cdot sin\theta$$ ...
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What is the three dimensional generalisation of a conservative force?

I was studying about conservative forces from a physics book (NCERT, a standard Indian textbook) and came to a para which is as follows: A force is conservative if it can be derived from a scalar ...
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Magnetic Dipole Moments and Dipole Contributions

I'm currently in Physics 2 (calc-based) at my University. On the last exam we had questions over magnetic dipole moments and dipole contributions. I'm still unable to solve these problems. Would ...
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Energy of the system of similar charges

We know that two same charges repel each other. To stop the charges from going away we have to exert an external force and hence energy is used. But if in a vacuum two similar charges are placed near ...
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Can we detect a cyclic coordinate by just inspecting the Lagrangian?

I'm reading through Susskind-Hrabovsky's Theoretical Minimum. On page 126, where they are talking about cyclic coordinates, an example is given: Suppose two particles moving on a line with a ...
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The energy stored in capacitors in series [on hold]

If there is a capacitor of $2$ micro farad and $0.5$ micro farad in series and the charge on the combination of the two capacitors is $0.8\times 10^{-6}$ C. How would you find the energy stored on ...
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Can I 'add potential together'?

I have the Lagrangian function for a particle in an electromagnetic field $$L = \frac{1}{2} m \dot{\mathbf{r}}^2 + q \dot{\mathbf{r}} \cdot \mathbf{A} (\mathbf{r}, t) - q \phi (\mathbf{r}, t)$$ If I ...
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On work done by internal forces which is coming out to be not equal to zero

1) Let us consider a block which explodes due to some internal mechanism into two smaller fragments of equal masses.The system was initially at rest and now is having some finite kinetic energy(due to ...
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Strange factor of 2 in Hooke's Law [duplicate]

I was working on a PGRE practice problem: A brick of mass $m$ falls onto a masses spring with spring constant $k$ from a height $h$ above it. What is the maximum distance the spring will be ...
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Why electric potential energy at a point is the same as amount of work done to bring the charge to that point from infinity?

Let's consider a positive charge at a point in the space. Now, if we want to bring a another positive charge to a point within the electric field of the first charge, then we have to do some work ...
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Why potential energy of a non-relativistic particle in an expanding universe is $ma^2\phi$?

I have been reading a paper on neutrino clustering in an expanding universe: see section 3, particularly 3.3.2 of this paper. In this paper for non-relativistic neutrinos, which travel through a ...
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If voltage represents an energy difference between two points, why don't electronic appliances all use the same amount of energy?

As I understand it, voltage is an energy difference between two points. $$V_f - V_i = - \int \mathbf{E} \cdot d\mathbf{s}$$ But consider a toaster and a refrigerator each using their own 120V ...
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Energy inside charged conducting sphere

We know that energy of a solid(or hollow) conducting sphere sphere is KQ^2/2r this energy is distributed from r to infinite and we say that energy inside is zero... Now we know that electric field ...
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Virial theorem lmplies loss of potential energy

Learning equipartition theorem, I search related content on this web. But I stuck at some point when I look at this part: "However as we climb out of the potential well to large interatomic distances ...
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How to derive “a blob of water in space becomes a sphere” analytically? [duplicate]

I'd like to understand better the assertion that planets are spheres because of gravity. The thing which I believe is true, but don't completely get, is that any arrangement of a sufficient number of ...
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Can I add a classical potential to S-matrix

I'm a junior learner of QFT, and I wonder if I can add a classical approximated potential (like Coulomb potential) to a total interaction \begin{equation}V=V_{\mathrm{Coulomb}}+V_{\mathrm{internal}} \...
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Central Potential + Coupled Angular Momenta

I am considering a two-state system with a Hamiltonian of the form $$ H = \frac{p_1^2}{2m_1} + \frac{p_2^2}{2m_2} + V_a(|r|) + \bigg(\frac{1}{4}-\frac{S_1\cdot S_2}{\hbar^2}\bigg)V_b(|r|), $$ where ...
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What is the maximum theoretical efficiency of conversion of potential energy to kinetic energy and vice-versa?

Am looking at different techniques available for identifying sources of energy. As part of it, have the following question : What is the maximum theoretical efficiency of conversion of potential ...
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Conservative force as negative gradient of scalar potential

In Classical Mechanics by H. Goldstein it is mentioned that “To satisfy the strong law of action and reaction, $V_{ij}$ can be a function only of the distance between the particles $i$ and $j$, i....
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Spring mass damper system: Distance from equilibrium after applying velocity to mass

I have a spring fixed to a wall on one end and a mass object on the other end in its natural resting position. The question is how far does the spring stretch when a velocity $v_0$ is applied to it, ...
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For the potential difference, how is it that $V=W/Q$=$U/Q$ when $U$ and $W$ are negatives of each other?

I'm currently studying electric potential and am somewhat overwhelmed by all of the different equations and their iterations. For instance, the first definition I learned was that: $$\Delta{V}=V_b-V_a=...
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Electric Potential Outside of Two Infinite Sheets of Opposite charge density

If you have two infinite sheets of equal but opposite charge density, the electric field outside the sheets will be zero due to cancellation. This led me to initially think that the potential would ...
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Not able to understand a concept from Classical Mechanics by H. Goldstein [closed]

I was reading classical mechanics by H. Goldstein and I came across the calculation of total potential energy of a system of particles. I am not able to understand what this derivation is conveying ...
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Derivation of Conservation of Energy from Newton's Second Law [duplicate]

Given Newtons's Second Law: $$ \frac {d}{dt} (m \boldsymbol{\dot r}) = \mathbf F $$ How is it possible to derive the conservation of energy equation with a constant mass? That is how can you derive $ ...
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Establishing separate datums

In the following question, how are we allowed to define two different zero potential energy reference points?
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Modeling three-dimensional infinite well in classical mechanics

I am interested in modeling point particle using classical mechanics using variational principles so that it is effectively inside some region $\Omega \subset \mathbb{R}^3$ which is assumed to be ...
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Potential energy of an ideal gas

According to equipartition theorem, for ideal gas in thermal equilibrium, each vibrational mode will get $kT/2$ for kinetic energy and $kT/2$ for potential energy. But at the same time, we assume ...
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Deriving the Lagrangian of a set of interacting particles only from symmetry

In section 5 of Landau and Lifshitz's Mechanics book, they show that the Lagrangian of a free particle must be proportional to its velocity squared, $\mathcal{L} = \alpha\mathbf{v}^2$ using only ...
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simple work and kinetic energy problem (baseball)

problem says: A baseball player throws a ball with a mass of $0.150kg$ with a speed of $40.0 m/s$ and an angle of $30$ degrees. What is the kinetic energy of the ball when it reaches the highest ...
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Velocity-dependent potentials and the dissipation function

From this previous question Charge, velocity-dependent potentials and Lagrangian where the citation is shown at the page 22, §1.5 of the book Classical Mechanics of Goldstein, we read that "an ...
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1answer
47 views

Two Opposite Point Charges: Infinite Potential Energy?

If I had a fixed point-charge ($q_1$, +) and I placed another free-moving charge ($q_2$, -) some distance away, what is the potential energy between them? The opposite charges attract drawing $q_2$ ...
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Is potential energy always inversely proportional to separation?

This is a question from Class 11 Physics NCERT. The answer is that only graph (v) is correct and the reason given here is that potential energy varies inversely with separation. But does that always ...
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If magnetic force can't do any work, then how can we define a potential?

I am confused about the idea that magnetic forces do no work. If something has a potential, then it has energy and hence can do work. I am using the logic of electric fields for this reasoning. I have ...
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Simplified formula of potential energy giving different expected value of mass

I am trying to calculate the mass of a planet by the following image I have the mass of the object, $2$ kg, and the radius of the planet, $5000$ km (also the gravitational constant $G$). My first ...
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51 views

Relation between electric potential and Electric field

I'm unable to understand why the integration of $\mathbf E$ is done in two different ways for constant $\mathbf E$ and varying $\mathbf E$, as in case of parallel plate capacitor and spherical ...
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Energy change as ball rolls down a curved ramp [closed]

At the top of the ramp, the ball has gravitational potential energy. As the ball rolls down the ramp, the potential energy converts to kinetic energy. Due to friction, some energy is also converted to ...
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Is the statement that $U(x)$ is quadratic for simple harmonic motion equally strong as the statement that $F(x)$ is linear?

Is the statement "If the potential energy of a particle under oscillatory motion is directly proportional to the second power of displacement from the mean position, the particle performs a ...
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Energy stored in an inductor [duplicate]

When we place an inductor in a circuit it opposes the change in current in that circuit. For increasing current in that circuit some work needs to be done against the inductor. This amount of work ...
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Ambiguity between electric potential and voltage?

I understand that electric potential is a location based measure of electric potential energy per unit charge in an electric field, and that voltage is then the difference between two electric ...
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Work - Energy confusion when movement is vertical/up a slope

I've always thought of work done on an object as the energy transferred to it. This explanation, however broke down when I came across the following situation : A block of mass $m$ is transported to ...
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Potential energy of system

when a spring is connected with a block if we compress the spring the potential energy of block changes. But if we take only the block as system then no internal conservative force is acting on system ...
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Energy stored in a field - isolated system

If I consider an isolated system, e.g. two masses, i know I can apply the energy conservation principle considering the kinetic energy and the gravitational potential energy of the two masses. But to ...
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Is the strong potential repulsive for high distances?

The negative region in a potential is attractive and the positive region is repulsive. At least in case of the coulomb potential: When having a look at the strong potential it is obvious that the ...
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Role of the Yukawa potential

What is the Yukawa potential converging to zero? Afaik the strong potential rises with the distance between quarks, hence, it should rise accordingly.
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Why is there a 1/2 in the expression for electrostatic energy U?

The expression for electrostatic energy is $$U= \dfrac{1}{2} \times \int \rho\,\phi\, dV$$ where $\rho$ is the charge density and $\phi$ is the potential at that point in ($dV$) Let me explain what I ...
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Work Done and Potential Energy in Electrostatics

This is a question from class 12 Physics NCERT Part 1: I am having so much trouble with this, I can't figure out where I'm going wrong. I solved part (a) here: (a) U= -27.2 eV (b) Here, the kinetic ...
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Components of Electrostatic energy to components of electric field?

I'm trying to understand the relationship between electrostatic energy and the electric field so that I can compute electric field components from electrostatic energy components. Is it correct to ...
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How does an object gain energy when it enters a potential field?

Conservation of energy says total change in energy is $0$. Let's assume a small object is in outer space (maybe like a football). It moves towards a planet (assume planet has no atmosphere for ...