# 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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### Minimizing the action - particle in a potential well

Consider a particle starting at rest in a potential well, the problem is restricted to one dimension. The lagrangian is $L=T-V$, set $V$ to 0 in the starting location, we get $L(t=0)=0$. If the ...
1 vote
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### How to Calculate the Stopping Distance of Train on a Complex Track [closed]

I am attempting to determine when a train should begin braking to reach a certain point at a complete stop. There are several factors that need to be considered that make this more complicated and I ...
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### A man standing in an elevator at the third floor of a building. What is the primary factor that determines the man's kinetic energy?

Misconception in Elevator Kinetic Energy Question I recently encountered the following question in a physics entry test exam: Question: A man standing in an elevator at the third floor of a building. ...
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### Emotional Energy Theory [closed]

Emotional energies are those whose action modifies us on an emotional level, they can make you feel euphoric, tired, energetic, irritable... Zeroth principle: If you are in sensory contact with an ...
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### Discrepancy in answers regarding a problem on adiabatic expansion of an ideal gas [closed]

One mole of an ideal gas ($C_{v,m} = \frac52 R$ ) at $300 K$ and $5 atm$ is expanded adiabatically to a final pressure of $2 atm$ against a constant pressure of $2 atm$. Final temperature of the gas ...
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### Work done by a spring on objects of different masses [closed]

If a spring is compressed between two trolleys of masses m and 4m on a smooth one dimensional surface is released, will the work done on both masses be equal regardless of the trolleys' masses?
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How Scientist Discovered that energy in the system is a constant things without doing any work it doesn't change? Also why KE is $(1/2) mv^2$?
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### What wouild the fail points be prohibiting construction of a photonic capacitor for use as a power source? [closed]

Physical considerations for construction of a basic photonic capacitor. Arbitrary shape and structural materials. (For example purposes- could be a 4 inch diameter evacuated aluminum sphere ...
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### Energy Conservation Spring Problem [duplicate]

One end of an unstretched vertical spring is attached to the ceiling and an object attached to the other end is slowly lowered to its equilibrium position. If S be gain in spring energy and G be loss ...
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### How hot can one heat a single atom?

Imagine a single hydrogen atom in an infinite vacuum being hit by thermal radiation from all directions. Then we crank up the heater, increase the radiation, and continue to do so without limit. Q1. ...
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### What does the equation of the law of conservation of total mechanical energy with deformation energy look like?

I considered task with elastic collision of two balls ($m$ and $M$) on horizontal surface. It needs law of conservation of total mechanical energy and law of conservation of momentum to solve this ...
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### When do we use $ΔU = mcΔT$?

So we usually use $Q = mcΔT$, and in a specific task they used $ΔQ = ΔU + ΔW$ and wrote ΔQ = mcΔT + pΔV. So basically ΔU = mcΔT. I am a bit confused on what formula to use for ΔU when? I have been ...
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### Would conjectured warp drive bubbles protect space craft interiors from collision with space debris?ris?

I seem to have read (unable to cite source) that a vessel in a curved spacetime bubble would accumulate radiation forward to the direction of travel and external of the bubble interior. The question ...
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### Motion of the COM of 2-body system

We have a block on a wedge like this; The block is given an initial velocity $v$,and the wedge is also movable . So when the block reaches its maximum height on the wedge,the block and wedge are both ...
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### What is energy, and why and when is it conserved? [duplicate]

In which field of physics can I find a solution to this question: What is energy, and why and when is it conserved? When I asked a similar question to my professors and peers, they said, 'We ...
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1 vote
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### What is the potential energy and kinetic energy for capacitor and inductor?

I always thought that $\frac{CU^2}{2}$ is potential energy stored in a capacitor and $\frac{LI^2}{2}$ is kinetic energy stored in inductor. But here and here (page 12) as understand it correctly for ...
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### Vacuum energies in different colliding vacuum bubbles?

I got two questions regarding this paper There, it's analyzed how colliding vacuum bubbles could result in new bubbles and how could this affect their vacuum energy. Specifically, it considers an ...
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### The kinetic energy of rigid body

I need to determine the kinetic energy of ball rolling with out slipping on a cylinder, and when I searched for it I found that the kinetic energy is: $$T = \tfrac12mv^2 + \tfrac12I\omega^2$$ But ...
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### Minimum work done on a mass to take it along a path [closed]

A particle of mass 1 kg is taken along the path ABCDE from A to E (see figure). The two "hills" are of heights 50m and 100m and the horizontal distance AE is 20m while the path length is ...
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