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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Capacitor charge [on hold]

It takes 14.8 J of energy to move a 13.0-mC charge from one plate of a 17.0-μF capacitor to the other. How much charge is on each plate? Assume constant voltage.
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30 views

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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12 views

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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3answers
31 views

How can I calculate how high an arrow goes when all I know is its initial speed?

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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1answer
62 views

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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0answers
11 views

Hydro electric energy transformation

Suppose you have a water source of 2L/s at a given altitude. Suppose you carry that water down to a reservoir 200m below. At that point you settle a hydro electric water turbine to convert the energy ...
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1answer
32 views

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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1answer
30 views

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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35 views

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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1answer
41 views

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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23 views

What happens to the average kinetic energy if you double the temperature?

I've always wondered what would happen to the average kinetic energy if you double up the absolute temperature of an ideal gas. My hypothesis is that, since the temperature is proportional to the ...
2
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1answer
7 views

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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0answers
9 views

Energy, Power, normalized time-series [on hold]

Given the following (productino of an energy-plant): Total energy production for a year (in Wh) Normalized hourly production ( 0 - 100%): For every hour a value: 100% means full production; 0 % ...
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4answers
116 views

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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1answer
20 views

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 ...
2
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2answers
53 views

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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15 views

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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0answers
10 views

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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0answers
34 views

If quarks are fundamental, and mass is a form of energy, then can quarks/leptons be pure energy? [on hold]

So, if quarks and leptons are fundamental particles, then could quarks/leptons be pure energy?
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1answer
26 views

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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2answers
65 views

How do I remove the negative sign from this derivation?

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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2answers
28 views

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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0answers
56 views
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1answer
19 views

0.19 kg apple falling (a problem on Work and Power) [on hold]

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 ...
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24 views

Specific Heat capacity [on hold]

The total heat capacity of a caloriemeter, heater, stirrer is 107 joules per kelvin. Mass of the liquid in caloriemeter is 0.241 kg. The power supplied by heater is 41.48 watts. The initial rate of ...
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1answer
24 views

How is there GPE in objects that are on top of a hill?

What I don't understand about gravitational potential energy is that objects have the greatest GPE on top of a hill and it decreases as they go down the hill. At the top of the hill, they are on the ...
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1answer
39 views

How does parallel plate lose energy when deflecting charged particles

Say you have a parallel plate setup, each plate is charged with ±Q of charge, and is then disconnected from the power source and is insulated from the environment. There is no way the plates can be ...
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1answer
36 views

Energy of electromagnetic wave

Its given here that energy density of an electromagnetic wave is $$\vec S=\frac{1}{\mu}(\vec E\times\vec B)$$ How is the above expression derived? And when did energy become a vector? I though work ...
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1answer
31 views

Where are the electron exchanges happening in solar cell physics when considering the photon?

When considering solar panel physics, are we taking an electron from Light(photon), or is the energy of Light causing an electron to jump in said solar cells through excitation? Is the photon even ...
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1answer
40 views

Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
3
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1answer
39 views

Can the internal energy of an ideal gas system increase as temperature decreases?

If $\Delta U = Q + W $ Then adding $x$ moles of an ideal gas of lower temperature into a system of internal energy $U$ would increase $U$ as the kinetic energies of the molecules of the colder gas ...
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0answers
30 views

Calculating the data rate for a baud signal [closed]

I have been working on these questions for the past few hours. I am working on calculating the data rate of baud signals, where each symbol can take on one of two levels. I wanted to know if I have ...
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3answers
68 views

is the potential energy of a black hole infinity

It appears like black holes posses an escape velocity greater than the velocity of light. It takes an atom infinity energy to travel at speed of light.Do black holes posses that energy to retain ...
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1answer
50 views

What would happen if you were to release the energies of the big bang in our universe a second time? [closed]

Would it just wipe out everything, or would something else occur?
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0answers
42 views

Can the linear momentum of a system be constant, even though its centre accelerates?

My instructor says if the velocity of center or mass is constant, it means that the linear momentum of a body is conserved. So if no external force acts on a body, there is no change in the linear ...
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1answer
26 views

“Carbon capture into fuel” - where does the energy come from?

I recently found an article titled "Scientists find a way to convert Carbon Dioxide from air into fuel" (here), and my immediate reaction was "surely not - the energy balance would kill you right ...
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1answer
33 views

Why am I not shocked when I touch a tree, and the tree touches a power line? [closed]

Why am I not shocked when I touch a tree, and the tree touches a power line?
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1answer
17 views

How could the BOE (barrel of oil equivalent) be measured?

The barrel of oil equivalent was given as an example of gigajoule scale energy. "The barrel of oil equivalent (BOE) is a unit of energy based on the approximate energy released by burning one barrel ...
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0answers
50 views

If a system has an internal energy equal to 0, does this mean it doesn't exist?

Enthalpy is a measure of energy in a thermodynamic system: It includes the internal energy, which is the energy required to create > a system, and the amount of energy required to make room for it ...
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1answer
49 views

What makes cart with a moving object in it gain speed (no friction anywhere)?

I would like to understand what makes the cart below the moving object move. There is no friction between any of the objects. The cart is moving therefore there is force applied to it. The only force ...
6
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1answer
42 views

If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
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1answer
21 views

Microwaving two products based on individual instructions

Suppose I have a cake, which has instructions to heat it for 60 seconds in the microwave. I also have some custard, which has instructions to heat it for 30 seconds in the microwave. For convenience, ...
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1answer
25 views

Actual electricity usage to maintain a constant water temperature

How can I easily measure (or determine) the actual electrical usage necessary to keep a constant temperature for my water heater?
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17 views

Which ball travels further, one that is thrown up a frictionless ramp or one that is thrown in the air? [closed]

They are thrown at the same angle, and their masses are equal. Please explain using basic physics, if you can. We only learned: Kinetic, potential energy Work Velocity
3
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1answer
100 views

How likely is negative energy to exist?

Negative Energy is the exact opposite of ordinary energy as it would move in the opposite direction from its momentum and accelerate in the opposite direction of an applied force. It would also warp ...
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1answer
64 views

Does this count as a proper derivation of the formula for work and kinetic energy? [closed]

$v_{av}$ = average velocity, $d$= distance, $a$ = acceleration, $m$ = mass Given: $$v_{av}*t=d$$ $$t=\frac{v_f-v_i}{a}$$ $$v_{av}=\frac{v_f+v_i}{2}$$ Then: $$\frac{v_f+v_i}{2}*\frac{v_f-v_i}{a}=d$$ ...
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1answer
77 views

Photons Disappear and Reappear from Atoms?

Where does photons come from and disappear to? Can photons be destroyed and created? Without atoms would photons exist?
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1answer
55 views

Why do we hear the square of the wave?

Assume we superpose two waves of frequencies $\omega_1, \omega_2$. Then what we get are beats. Adding the two sines gives us $$\psi = A\sin(\omega_1 t) + A\sin(\omega_2 t) = 2 \sin ...
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37 views

Calculating potential energy per ion of an one dimensional ionic crystal

The problem states to calculate "the potential energy, per ion, for an infinite 1D ionic crystal with separation $a$"; the crystal is a 1D lattice of alternating charges, likes so: ...
3
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0answers
19 views

How to efficiently cool down simulated gas by time-dependent potential?

I'm trying to simulate condensation of a highly diluted gas (a model gas, not any real one). For simplicity I restrict the simulation to 2 dimensions. To setup the simulation I take some interparticle ...