Questions tagged [energy]

Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding the [energy-conservation] tag if it is specifically about its conservation.

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Does the 1/2 coefficient in kinetic energy stem from Newton, the De Broglie wavelength and length contraction?

This is my thinking. Everything has a De Broglie wavelength. From this the energy of an object can be calculated. Now due to Special Relativity anything with a velocity experiences length contraction. ...
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If you have the same amount of water filled in pails [closed]

If you get identical pails filled with the same amount of water at the same temperature, and mix the hot water from the cup with that of the water in pail #1 and the hot water from the kettle in pail #...
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Does dark matter act gravitationaly to itself. If Yes, why does not form more compact objects? [duplicate]

Does dark matter act gravitationaly to itself.If Yes, why does not form more compact objects? Can this be explained as its components have enough kinetic energy to overcome the collapse?
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How can work done be equal and opposite when the forces are unequal and object travels the same distance

Let's suppose we have a spring fixed to a wall, attached to a block and nothing is said about the forces acting on the block or spring. It's known that if the block is displaced in the positive ...
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How cup of water and boiling water inside a kettle dont contain the same amount of energy? [closed]

A cup of hot water with a temperature of 100 degrees Celsius has the same temperature as that of the boiling water inside a kettle but they don’t contain the same amount of heat energy. Why is this so?...
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Why doesn't particle-antiparticle annihilation violate conservation of energy? If the particles appeared from the vacuum, and leave behind gamma rays?

I noticed a 'Similar Question' above, when posting this, but I am interested in the conservation of energy part.... I know I was taught (and have repeatedly read) that virtual particles aren't ...
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Can hydrogen last longer in a tank if a liquid is used as a barrier near the faucet? [closed]

Can hydrogen last longer in a tank if a liquid is used as a barrier near the faucet? And also a second question: what liquid can block hydrogen leakage?My question is not about engineering but about ...
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Is black hole really powerful than light from a star? [closed]

Light from a star is so powerful energy that it travels large distances in vaccum. Blackhole is so powerful that it can attract light. If a star is near a blackhole, the blackhole would completely ...
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Conservation of angular momentum in an inelastic collision

I have a question about the second method used to solve the problem above. The moment of inertia with respect to the stick's midpoint after the collision is $ml^2/12 + ml^2/4$ or $ml^2/3$ so the ...
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Bound States of a Particle in a Half-Infinite Potential Plus a Delta Function [closed]

I am having some conceptual problems regarding the bound states. I will try to address them using a simple problem. Consider a particle which is under the effect of a half-infinite potential plus a ...
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Conservation of energy to find the total distance a block travels in a series of elastic collisions [closed]

I have a question about finding the total distance the block travels. To find the distance the block travels after the nth collision, I used the following approach. The speed of the block after the ...
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Why are eigenvalue asymptotics (or more generally, the counting of eigenvalues below a certain energy) important to physics?

I am a mathematician, and I have worked with time-independent Schrodinger operators; but I have little rigorous knowledge of classical mechanics or quantum mechanics. I know what eigenvalues and ...
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Will work be done by magnetic field?

lets discuss it in inductor topology? A1 and A2 are contacts to the ferrite core of an inductor .DC resistance of ferrite core is of the order of milliohms,the ac resistance is quite high to avoid ...
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What converts mechanical energy into kinetic energy? would it be a generator or a motor?

I know that mechanical energy is the sum of an object's potential and kinetic energy. Also know that a turbine (mechanical energy) coverts into electrical energy by use of a generator. So is ...
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Capacitor microphones for recording studios

This question is formulated exclusively for high school students precisely to interest them in a more concrete way. Condenser microphones are characterized by a capsule that functions exactly like an ...
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$D+T$ fusion-fisson hybrid using particle accelerators

I've been reading up on nuclear physics and I have this dumb idea that I can't seem to poke holes in. Imagine a linear particle accelerator accelerating tritium nuclei in to a water tank containing D$...
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How much energy is stored in the field of a hydrogen atom?

How much energy is in the electric field of a single lone hydrogen atom that has no neutrons and exists at the lowest energy state possible? Well in a universe where nothing else exists.
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Spring potential energy problem [closed]

A diver with mass 55kg jumps 0.8m into the air. She lands on a diving board that bends down a deflection of 0.4m. What is the potential energy of the diver at the top of her jump? How fast is the ...
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Will the change in kinetic energy during projectile motion always zero?

Will the change in kinetic energy i.e. $\frac{1}{2}mv^2-\frac{1}{2}mu^2$ always zero in case of projectile motion since the initial speed and final speed is the same that is $u$? If my observation is ...
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1answer
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Can a photon with energy value not corresponding to the discrete energy level differences excite an atom? [duplicate]

I'm a sophomore majoring in physics, and I had some question about the discrete energy value of atoms and its excitation. So, I know that in order to make a hydrogen atom in a ground state to get &...
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Why can circular motion not be used to calculate kinetic energy of a person standing on Earth?

I did this question: In a sense we all have kinetic energy, even when we are standing still. The earth, with a radius of $6.37×10^6 \mathrm m$, rotates about its axis once a day. Ignoring the earth's ...
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Why is displacement shown in the picture below $y1-y2$ and not $y2-y1$? [closed]

I am having a hard time understanding why is the displacement in the formula of work shown in the image y1-y2? Isn't displacement final value - initial value?
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What would the lifestyle be of a person (energy requirements of that lifestyle) living in a world with a successful Dyson Sphere? [closed]

Let's say I want to live in a world with unlimited clean energy. What would be my energy requirements, for: - Building a house purely with robots (including beds, furniture, fans, electric sockets ...
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Space debris impact

Given two pieces of aluminum, a sphere with diameter $d$ and a plate, how can we estimate the penetration depth given the initial velocity $v$ of the sphere? If that proves too complicated due to ...
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Motion of a body under the influence of increasing magnetic field and a spring

I came across a problem as follows: A particle of mass $m$ and charge $q$ moves on a circular path on the surface of a frictionless table with speed $v$ where a magnetic field $B$ exists uniformly ...
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Why is electric heating considered a work interaction?

The textbook I am currently reading Thermodynamics: An Engineering Approach by Cengel & Boles classifies the energy transferred to a system by an electric heating element as a work interaction ...
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Could there be a property related to the velocity cubed, like there is momentum and kinetic energy? [closed]

There is a property represented by $mv$. There is a property that is represented by $\dfrac{mv^2}{2}$. Is there a property (or could there possibly theoretically be one) that is represented by $\dfrac{...
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Does movement of a charged particle in a electric field imply electric potential energy?

A particle at rest with charge $q$ and mass $m$ is placed in the center of a spherical shell with surface charge $-\rho_s$ on the top half and $\rho_s$ on the bottom half (see image). The particle ...
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1answer
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Absorption and emission spectra - regarding excited state of electrons

I had a question regarding the "excited state" of electrons. I know that electrons can jump up from their ground state to higher energy levels if given a specific amount of energy. But what ...
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Why is the term instantaneous work not defined?

I was reading a textbook and found the statement that said that there is no such term as instantaneous work, however the textbook does not give a reason as to why it cannot be defined. To me it sounds ...
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How can you do work on a control volume with a fixed boundary?

I am having trouble understanding the concept of flow work. All of the texts and online sources I have read so far claim that flow work is always done on or by a control volume where matter flows ...
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1answer
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Why is over-damping non-oscillatory?

I have read that the during overdamping the damped forces or the resistance to movement of an object in S.H.M is so high that if the object is displaced from ita mean position then it returns to it ...
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Conservative and non-conservative forces

We define two classes of forces, namely conservative forces and non-conservative forces. When we do work against non-conservative forces , then our work is dissipated in the form of heat, sound or ...
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How to calculate the total energy from a given wavefunction?

For a given wavefunction, $\Psi(x,t)$ of a system, how one can calculate the total energy? For example, the wavefunction for a particle of mass $m$ moving in a certain potential $U(x)$ is given by: (...
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What does Lagrangian actually represent? [duplicate]

$L=T-U$ Here, $L$ is Lagrangian. $T$ is kinetic energy. $U$ is potential energy. But, what Lagrangian actually is? I know what Holonomic and non-holonomic is. But, I was thinking what the Lagrangian ...
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1answer
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How does a body "carry" kinetic energy?

I have heard that photon is an oscillating electric field that carries a quanta of energy, so is there any such particle to carry macroscopic energy (such as kinetic energy, potential energy, etc)?
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Energy in special relativity [duplicate]

Imagine a spaceship travelling near the speed of light relative to observer on the ground. a candle is burning inside the spaceship and it takes 3 hours for the candle to burn completely relative to ...
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1answer
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Contradiction of Units in Polytropic Process

A polytropic process is a process that obeys the relation $pV^n=C.$ However, when I try to solve a problem involving this relationship with, for example, $n = 1.5$ my use of units in my equations ...
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Gibbs energy and compression ratio

I came across a very interesting Gibbs energy-based interpretation about the importance of compressing the fuel before combustion in an engine (Kennesaw State University, [1]). However, while the ...
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Is there any kind of "radar" system That can detect electrical fields / electricity

I may be using improper terms here, but Is there any kind of "radar" / non-contact system That can detect electrical fields / electricity? see fig for clarification to what I'm talking about....
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Is there any physical system where the kinetic energy is imaginary?

Is there any physical phenomena where the kinetic energy comes out to be imaginary?
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What provides energy in mutual inductance to unconnected coil

In this mutual inductance setup: when current is passed through coil 1 the flux through coil 2 changes for a short amount of time which induces a current in coil 2 the direction of which, in ...
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Energy eigenvalues of isotropic 2D half harmonic oscillator

What are the energy eigenvalues of isotropic 2D half harmonic oscillator? $$ H = \frac{p_x^2}{2m} + \frac{p_y^2}{2m} + \frac{1}{2}m\omega^2 x^2 + \frac{1}{2}m\omega^2 y^2, \quad x > 0, y > 0 $$ ...
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Stored energy of a capacitor

Imagine the two terminal of a parallel-plate capacitor are connected to the two terminal of a battery with electric potential difference $V$. If the capacitance of the capacitor is $C$, and the area ...
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Making sense of Entropy being energy over temperature

Over the internet, I found many resources that explain very well what entropy represents. However, the dimensions still appear hard for me to make sense of: energy, simply put, is the ability to do ...
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Block-Spring equilibrium question [duplicate]

I had the question- A block of mass $M$ is attached to the lower end of a vertical spring. The spring is hung from a ceiling and has force constant value $k$. The mass is released from rest with the ...
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Help with derivation of Kinetic Energy of N point masses

There are $N$ point masses as shown in image each with mass $m_i$ and velocity $v_i$. We need to find the Kinetic Energy of the system. Here is the proof attached I have some doubt in it. The doubt ...
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1answer
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Energy conservation for changes in the Hamiltionian

If the Hamiltonian represents the total energy of the system, then how does it change? Does a change in the Hamiltonian violate the conservation of energy? Of course, we know from the Hamiltonian ...
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2answers
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If temperature is proportional to average kinetic energy, then is the air around me actually at a higher temperature than, say, my table?

I know that thermometers work by conduction, meaning that the particles in the alcohol inside the thermometer will always get to the same average speed of the particles of the surrounding substance ...
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1answer
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Can voltage be considered simply a conversion factor?

Please correct my logic or lack thereof. It seems to me voltage or potential difference is only a conversion factor between charge and energy. Here's an example: Suppose 10 elementary charges are ...

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