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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What role did the Higgs boson play in the Big Bang?

Scientists say that inflation stopped when a very peculiar energy was mobilized, did Higgs boson play any role in this? What is it's relation to the Big Bang? Some physicists, such as Michio Kaku, ...
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225 views

How can the bodies attain same velocities during the max. deformation during collision?

My book writes: Collision between two bodies is almost similar to the case where there is a spring between the two colliding bodies. At the instant they come into contact , the rear ball has a ...
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Why can't we store light in the form of light?

We can store cold (ice), heat (i.e. hot water bag) and electrical charge (batteries). We can even "store" a magnetic field in a magnet. We can convert light into energy and then, if we want, back to ...
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Estimate of the second shallowest bound state?

Suppose we have a 1D potential $V(x)$ of finite range, i.e., $$ V(x) ~=~0 $$ for $|x| > b $. The potential is assume to support at least two bound states, but might have more, say $n\geq 2$. ...
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1answer
59 views

Why is energy of emitted particles negative?

recently I had one problem here, and in comments I got interesting thing written by user Sofia. Unfortunetly, the topic is in hold now and I can't ask her more. Here is the comment: Radio-activity ...
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Work done after explosion of chemical bomb

Question: Suppose, a chemical bomb is stationary. Then it explodes into n parts in all direction. What is work done? My Efforts The bomb is stationary, so momentum and and kinetic energy is 0. ...
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1answer
225 views

Physical Meaning Of $ dQ/T $ Regarding Clausius Inequality: Is it related to Energy Loss in form of heat or Something Else?

What is the physical meaning of term $ dQ/T $ in Clausius Inequality $ dQ/T \le dS $ ? Physically we can relate entropy to number of microstates of a system, which relates to number of possible ...
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1answer
58 views

What would Negative Energy act like? [duplicate]

So I heard that if you want to make a wormhole you need negative energy. What is special about Negative Energy that allows it to do that? What are the properties of Negative Energy compared to normal ...
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2answers
1k views

Elastic Collision And Momentum

The question I am working on is, "Two blocks are free to slide along the friction-less wooden track shown below. The block of mass $m_1 = 4.98~kg$ is released from the position shown, at height $h = ...
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2answers
372 views

Kinetic energy question

Thought experiment: I am starting to walk on a corridor. From the corridor's perspective I have a certain increase of kinetic energy. From my perspective the whole universe is gaining kinetic energy ...
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1answer
579 views

Does a rotating plank only acquire rotational kinetic energy?

I have another doubt with a Kleppner problem :(. A thin plank of mass M and length l is pivoted at one end. The plank is released at 60$^{\circ}$ from the vertical. What is the magnitude and ...
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2answers
3k views

How can you calculate (or convert) the Wh of a capacitor whose energy is given in Farads

When trying to compare the energy in a battery to the energy in a capacitor, the units don't match up. How can one compare a battery whose Ah are 10 and Voltage is 3 (for a total of 30 Wh) to a ...
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132 views

Energy of an Analog Signal

I would like to know why we are not calculating the negative energy of a signal.For example for $sin$ wave there is both an positive and negative phase.But while we take the energy of the signal we ...
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4answers
4k views

Why do we calculate energy by integrate the Signal squared?

What's the interesting thing in the square of a signal? I know integrating gave us the sum of the differentiated energies, but why the Energy is the square of the signal?
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2answers
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Energy of a signal

"The energy" of a signal $x(t)$ is defined as : $$E_s = \int_{-\infty}^{\infty}|x(t)|^2$$ Why is it called energy if it's not homogeneous to energy ? What does it actually represent ? Parseval's ...
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1answer
85 views

What (if any) state did energy exist in prior to the big bang? [duplicate]

I am comfortable with the idea that 'pure energy' cannot be observed, only different forms in which it manifests. I can also understand that matter-antimatter interactions result in fundamental ...
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1answer
211 views

Conservation of momentum 1-D problem: track is not level

This problem is a standard kind of 1-D problem. You have 2 equal carts approaching each other and collide on linear air track. BUT the person setting up the track did NOT do a good job at making the ...
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1answer
85 views

Can we measure kenetic energy on an absolute scale, or does it have to be measured with reference to something else?

I recently read the question Kinetic energy of an object at rest where it was suggested that the kinetic energy of an object on Earth is measured in the reference frame of Earth. Can we measure ...
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1answer
98 views

Will a heavier or lighter tank shell / bullet/ etc. travel further given the same starting energy?

Let's say I have for example two tank shells, both being the same size and having the same shape. Let's say the starting energy is 100kg*m/s^2, and the one shell is 1kg, the other 25kg. 1kg * ...
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2k views

Kinetic energy of an object at rest

Why don't we consider that an object on Earth has kinetic energy as it is also moving at the rotating speed of Earth?
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3answers
129 views

Can time be calculated without actually involving any matter?

Humans typically measure time by the change in material things. The movement of hands on a clock. The oscillations of a cesium atom. But can time also be measured by just changes in energy, and in ...
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1answer
72 views

Out of phase AC transmission lines in parallel

I've been reading up on power transmission networks and came across this thing. http://en.wikipedia.org/wiki/Quadrature_booster Basically it balances the load between two parallel power lines by ...
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0answers
66 views

Making An Energy Momentum Plot For A Rashba Model (Using Discretization)

I want to make a plot of the Energy versus the Momentum of the Rashba model, using discrete matrices. First Ill show how I did this for the free particle. Subsequently I will show what goes wrong for ...
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What is the true fundamental 'stuff' of physics? [closed]

It seems to me that most if not all of the publications and the institutional education of physics 'jump in' and start describing detailed phenomena without spending too much time describing and ...
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2answers
500 views

Ground state of Spherical symmetric potential always have $\ell=0$?

I was given a problem where I have a spherically symmetric potential (the exact form is not relevant to this question, I think - but anyway is it 0 for $r\in[a,b]$ and $\infty$ everywhere else) and I ...
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4answers
297 views

Question about dot product of four vectors?

I am looking back over some old notes and see that I have written $\bar{p}=\left(\overset{E}{\vec p}\right)$ and $\bar{x}=\left(\overset{t}{\vec x}\right)$ (using Plank units) And then $\bar{p} ...
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2answers
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Is the coefficient of restitution frame independent and energy conservation?

In this question I am ignoring relativistic effects. The following statements I think are true: change in Kinetic energy is not invariant under change of frame Force is invariant under change in ...
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1answer
292 views

How to calculate the Impact of a meteor

I am trying to add a dose of realism to a story I'm writing: imagine an invulnerable superman-like being that won't disintegrate at any point, weighing in at 349lbs, travelling at 86,000mph through ...
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1answer
91 views

Can all energetic photon excite an electron?

Consider a hydrogen atom, to excite the electron to a higher orbit, it should interact with photons of energy equal to that of the energy difference between the two states. If the energy of photon is ...
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0answers
102 views

Force and Energy in robots

There are two similar and hypothetical robots that move with wheels powered by motors, Robot A and Robot B. Robot A has a gear ratio of 3:1 (The gear connected to the motor is three times larger than ...
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0answers
45 views

Create a transmission protocol to transfer both data and energy(Wireless Communication)

Is there a protocol by which we can design systems that jointly transfer both data and energy ? Some kind of gadget that collects the received energy, temporarily stores it in a battery and later uses ...
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2answers
313 views

A simple quantum mechanics question [closed]

Here is the problem: Find the energy of neutron, electron and electromagnetic waves of wavelength 0.1nm. English is my second language, so I am kind of confused about the meaning of problem ...
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1answer
67 views

Where does the block get the energy from?

Let there be a block of mass $m$ on a frictionless surface. A boy of mass $M$ exerts an invariant force $F$ on the block & does positive work on the block by displacing it by $d$. By Law of ...
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2answers
222 views

translational energy levels

My textbook says translational energy level is so closed, and it basically covers the whole EMR spectrum, so any temperature beyond absolute zero is high enough for molecules to have translational ...
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2answers
16k views

What is the relation between kinetic energy and momentum? [closed]

If kinetic energy is doubled, what happens to momentum? Is it also doubled? I've tried working through the formulas for each but keep getting lost. $$KE=\frac{mv^2}{2}$$ $$p=mv$$ so if ...
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4answers
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How does lowering your thermostat save energy?

Say it is winter and the outside temperature is 0 degrees f. I set my thermostat to 74 degrees. When the temperature inside my home reaches 72 degrees, the furnace will kick on and warm the house to ...
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1answer
60 views

Finding energy stored in a capacitor

i am given a voltage time graph for a capacitor circuit. How to find energy stored in that capacitor at various time instants? Can we just calculate by using $\frac{1}{2}CV^2$ We are given capacitance ...
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1answer
724 views

Magnitude of work

I am a little bit confused on the concept of work. By definition, work done by a constant force of magnitude F on a point that moves a displacement s in the direction of the force is W = Fs. So lets ...
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2answers
732 views

Does “Infinite Universe” Imply Infinite Mass?

In accordance with the FLRW Metric with a curverature of $k=0$ (as observationally supported by several of NASA's experiments including WMAP, Planck satellite, DASI, etc.) the universe is spatially ...
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10answers
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What makes running so much less energy-efficient than bicycling?

Most people can ride 10 km on their bike. However, running 10 km is a lot harder to do. Why? According to the law of conservation of energy, bicycling should be more intensive because you have to ...
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5answers
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Why is there no relation between kinetic energy and momentum in collision of two bodies? [duplicate]

The statement that baffles me: During most of the collisions, part of the kinetic energy evolve as heat, nevertheless momentum is still conserved. Ok, the statement may be true. But what ...
2
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1answer
72 views

Change in velocity of a circular orbit?

For a body in a circular orbit will any (i.e. however small) decrease in velocity mean it falls to earth or will it go into an elliptical orbit? I originally thought that it was the first (i.e. falls ...
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1answer
153 views

Do you think it’s possible to make a power plant of the described kind?

We are working on a science project and try to engineer a power plant of a new kind. It is called Air HES (air hydroelectric station). The idea is described on our website. Do you think it is ...
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2answers
3k views

How to find height, when given the velocity at that location, starting height, and mass of object? [closed]

The question: A roller coaster is 100m above the ground, and weighs 1000kg. At one point of the roller-coaster-ride, the velocity is 28 m/s. What is the height of the roller-coaster at that ...
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3answers
2k views

What's the difference between Capacitors, Ultra-Capacitors and Batteries

Capacitors are known to hold and release energy very quickly, unlike the slower release that batteries exhibit. If one were to bunch many (1000's of) capacitors together could they function as a ...
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1answer
57 views

Why is there not a delta here in this formula about temperature changes

I have been taught and have seen this formula many times $$Q=m\cdot c\cdot\Delta T$$ Where $Q$ is the internal energy, $m$ is the mass, $c$ is the specific heat and $\Delta T$ is the temperature. ...
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831 views

Comparison between entropy and internal energy

Why is entropy change a better way of determining a spontaneous process compared to the change in internal energy?
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5answers
456 views

Is this expression for the kinetic energy of a spinning disk revolving about a second axis correct?

My question is motivated from a question from another user. You can see the configuration of the rotating system here: One disk/ring in double rotation and sum of energy. I am not interested in all ...
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1answer
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momentum and energy of the rods

I have two electromagnets and I attach them to two rods(same mass) such that, first one will be attached to centre of first rod and the second one will be to the end of second rod. Now I bring them ...
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3answers
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Making a plastic scintillator glow?

I have a plastic scintillator I had purchased off eBay, which is believed to be BC408 http://www.phys.ufl.edu/courses/phy4803L/group_I/muon/bicron_bc400-416.pdf Upon shining a small UV LED (10-40mA, ...