Tagged Questions

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 [tag:energy-conservation] if it is specifically about its conservation.

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How can I calculate the rate of mass air flow being supplied by the AHU in a room?

I need to calculate the mass air flow being supplied by the AHU so I can find the total heat being supplied to the room. However, I only have the following sensor measurement - Supply Temperature, ...
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Concept of Work & Energy with trolley Example

I was solving one question in which girl on trolley of certain masses sits. Then certain force is applied on trolley which made some displacement. In my opinion work should be done by both Girl & ...
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Energy of a body in circular motion?

I'm confused about energy of a body in circular motion. In particular I'm having trouble to find the correct answer to this question. Consider the body in the picture that is set in motion from ...
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Do gravitational waves contain actual energy and momentum? [closed]

Gravitational waves are waves in the fabric of space time and gravity is also caused by warped space time. So do gravitational waves contain actual energy and momentum?
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Energy of a waterfall

Why cannot a waterfall be considered to be never ending source of energy? A waterfall is converting it's potential into kinetic energy and if we "take out" some of it's kinetic energy while the water ...
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I ask all who know, because the internet is vague, what is the average energy efficiency rate of double glazed windows? I'm doing a school project on a design idea of making a school energy efficient....
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Conventions and realities of kinetic energy?

I am having doubts regarding why $1/2$ is present in kinetic energy and if this is conventional why cant we say potential energy is $2mgh$ and kinetic energy $mv^2$. So is this $1/2$ conventional or ...
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Amplitude at successive wavefronts?

Consider spherical waves emanating from a point source initially the amplitude is A, as wave travels forming wavefronts will the amplitude of each point in all the secondary wavelets be the same and ...
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How many water wheel can fit on a river until another one produces zero energy?

Mostly what I'm after are the factors I need to know to do the problem. Imagine we're in the days of Leonardo Da Vinci. And pizza is everyone's favorite food. And there's a river that goes on ...
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Bicycle Problem [closed]

A student watches two people coast down a hill on bikes. They both start from rest. Neither one of them peddles the bike. Gravity is the ONLY driving force. Friction and air resistance are negligible. ...
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A definition for relativistic energy without quantum mechanics

What are the minimal postulates to define energy in special relativity? Let us assume that momentum has not been defined yet (it can be defined from the energy in fact). I expect we are looking for ...
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Does the kinetic energy change depending on the direction of the velocity? [closed]

The kinetic energy is calculated with the following formula: $$E_k = \frac 12 mv^2$$ Does $v$ represent the value of the velocity? I mean, if you have a specific direction of the velocity is the ...
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How to use Special Relativity in simple numericals? [closed]

So I was recently thinking about what an electron's velocity would be after it was accelerated through a potential difference of 1 V. Doing simple calculations like just dividing its energy (which ...
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I'm learning Work-energy theorem, this question popped into my mind about Force applied and displacement [closed]

I know a lot but I'm not sure, I'm guessing if 400 J of work done on a 800 Newton object, if I'm correct, 400 N to 800 N... that is 0.5 m displacement, so by $W = \Delta \ KE$ why do I get 200 J? I ...
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Does an object move because it has Kinetic Energy or does it have Kinetic Energy because it is moving?

Maybe to explain I'm wondering if an object gains $\rm K.E.$ which causes it to have a velocity or does an object have a velocity which cause it to get $\rm K.E.$?
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Is Electron decay period less than stated?

Phys. Rev. Lett. 115, 231802 – Published 3 December 2015 sets a limit on the stability of the electron for decay into a neutrino and a single monoenergetic photon in $\tau\ge6.6\ 10^{28}\ \mathrm{yr}$....
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Finding moment of inertia of a *double* rotating sphere

I'm completly stuck here: my system consist of a sphere rotating in a ring. How do I calculate the moment of inertia of this system? I know the MOI of a sphere rotating around it's cog, but here, I ...
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plastic deformation and kinetic energy?

I am searching for a equation which i cant find on the internet .. its may be too simple to say but i want a relation between kinetic energy of an object and the deformation that it causes on a ...
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deformation and displacement by a collison? [duplicate]

In an experiment by Emilie du chatelet metal balls were dropped from a height on a clay bed only to find that the displacement of the clay material was proportional to the square of velocity of the ...
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Relationship between impact crater properties and kinetic energy? [duplicate]

William Gravesande in 1722 published an experiment in which brass balls were dropped from varying heights onto a soft clay surface. He found that a ball with twice the speed of another would leave an ...
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Is work only a change of kinetic or potential energy?

I find out on the internet that work is a transfer of energy essentially kinetic. What is the use of work if it does not consider all the types of energy applied , i mean sometimes an objects internal ...
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How to test the brightness of the light bulb?

I am working on the project using different kinds of wires, like copper lead silver and testing the brightness of the bulb using different wires. Can anyone please let me know how to test the bright ...
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Total energy of the fluid

Consider a one dimensional system with fluid in it. Mass and momentum balance equation of the system are (in the absence of external forces and assuming Newtonian behaviour valid for viscocity), \...
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Why do non-hydrogen atomic orbitals have the same degeneracy structure as hydrogen orbitals?

The solutions of the Schrödinger equation for hydrogen are the "electronic orbitals", shown in this picture: (source) They have the following degeneracy structure: (source) It is often said that ...
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Photons can be regarded as particles?

So I've been reading an article and stopped at this sentence : "Likewise, we can take energy (such as particles of light, called photons) and turn it into matter." He gave an example of energy which ...
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Is energy only an idea? [duplicate]

Physicists say that energy is the ability to do work, and work is moving something against a force, like gravity. But what is energy? Is it something real? I know I will be criticised for using that ...
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Whats is the relationship between energy of an atom and its magnetic moment?

I'm working on a problem that says that If $\varepsilon_{\pm}=\mp (\mu \mu_0 H + k \theta \frac{M}{\mu N} )$ is the energy of the atom of a specimen that can orient itself either parallel or ...
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Calculating Potential Energy

I'm familiar with the potential energy equation, but I'm concerned with the value of 'g' in it. I know that, at sea level, earth's gravitational acceleration is 9.81 m/s/s. So I know that within the ...
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Acceleration needed to make a solid turn into gas? [closed]

There's a joke in a show in France where it is said speaking of a human that he would turn into gas if accelerated enough. My questions : Is this possible without friction ? What would be this ...
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How can gravitational waves dissipate the energy carried by them? [duplicate]

I am not an expert on GR or gravitational waves but i have been reading about them and i wondered about where and how do these gravitational waves dump their energy? I read that the black hole ...
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Is the $I^2R$ when a resistive heating element is cool the same as when it's hot?

My system (electric resistance element and water bath) heats up 2 degrees in 20 seconds (0.1 deg/sec) when the resistance element if fully heated. Say I want to raise the temperature 0.1 deg every ...
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Strength of moonlight

So I read this xkcd, and thought it was kind of cool. However, I showed it to my engineer father and physics undergrad brother and neither seem to find the explanation very convincing (though they ...
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Which requires less energy, complete mechanical breaking or vaporization of matter?

Let's say we have a one kilogram piece of rock. Now if we want to separate each molecule from the other molecules making this piece of rock, which method requires the least energy while neglecting ...
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Calculating the solar produce the right way

I am not quite sure on how to calculate the following. We've got solar panels on the roof and a data logger in the heating's room. The data logger is returning every 10 seconds the current energy ...
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How can I calculate how high an arrow goes when all I know is its initial speed? [closed]

I'm not familiar with English physics terms so bear with me. If I shot an arrow straight up and it went off with a speed of 21 m/s, how high up would it go? (air resistance is insignificant). My ...
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Where does gravitational waves' energy go?

Following the measurement of gravitational waves, many sources described them and explained they carry energy away. What I don't get is how this energy will get transfered back to anything else. If ...
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Confusion in a problem

This is a very basic homework type question. I guess there is some intermixing of concepts in my head. Help. There was a question I came across - A ball of mass 0.2 kg is thrown vertically upwards ...
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Rigid bodies and inelastic collision

If two rigid bodies collide - how the collision can be inelastic? where the energy goes? If the energy transffered to heat, doesn't it contradict that the bodies are rigid?
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Is all energy quantised?

I'm wondering if all energy is quantized? Can a particle with kinetic energy have any value of kinetic energy or is kinetic energy also quantized? My reason for asking this is that if a particle is ...
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Can two different objects or system of molecules have different temperatures, but having same internal kinetic energy?

If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and ...
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How is the energy spectrum of a gamma ray in a material?

I'm trying to solve the following problem for a course in radiation physics. A thin ray of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity and the energy of the ...
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How do they find the energy of a photon?

Is the actual energy of a photon ever measured? How is it done? I read that a photon is usually identified by diffraction, that means its wavelength is measured, is that right? In this way we ...
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What information does kinetic energy and work give us about a body?

When I studied momentum I learned that momentum says about a body how hard is it to stop it. In addition, I learned that impulse tells us in some way how much time would I need to stop the object. If ...
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What was the initial source of energy?

According to law of conservation of energy; "Energy can neither be created nor be destroyed but may change it's form" Where did the energy come from which led to the creation of universe by big bang?
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Energy losses of a ball, hitting the ground due to elastic and accelerating processes

There is a question about gravitational force and irreversibility. In my answer I pointed towards the phenomenon of photon emission during accelerations and by this of energy loss. My last sentence ...
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What is temperature dependence (Schottky defects)?

The problem requires us to use the following property to determine the temperature dependence: For a system in thermal equilibrium in a heat bath at temperature $T$ the Helmholtz free energy is a ...
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vibrational motion in gases

In a debate, I argued that vibrational atomic movement as cause of internal energy is prominent in solids (due to their crystal structure) and it is not prominent in gases. I think this also applies ...
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How do I remove the negative sign from this derivation? [closed]

A homework problem required me to show that the first equation below can be written in the form of the second equation. It was all fairly simple except for the negative sign. I'm not sure how this is ...
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Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
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0.19 kg apple falling (a problem on Work and Power) [closed]

Problem A 0.19-kg apple falls from a branch 3.5 m above the ground. a) Does the power delivered to the apple by gravity increase, decrease, or stay the same during the time the apple falls to the ...