Energy is a quantity which gives an overview of the amount of work doable by the system.
3
votes
3answers
305 views
Energy, Lifting Weights with Noether?
Is there an easy (aka intuitive) way to understand that the conserved quantity from time translation symmetry is just what we call energy?
In other words, we use two definitions of energy. One is ...
0
votes
3answers
72 views
How do you determine the heat transfer from a P-V diagram?
I doubt this question has been addressed properly before, but if there are similar answers, do direct them to me.
I am currently studying the First Law of Thermodynamics, which includes the p-V ...
0
votes
2answers
60 views
Why is potential energy negative when orbiting in a gravitational field?
I had to do a problem, and part of it was to find the mechanical energy of satellite orbiting around mars, and I had all of the information I needed. I thought the total mechanical energy would be the ...
0
votes
2answers
144 views
Perpendicular Elastic Collision (different masses, different velocities)
I'm stuck on a mechanics problem and I can't make any headway past momentum and kinetic energy being conserved. Here is the problem:
Two hover cars are approaching an intersection from ...
0
votes
2answers
354 views
From knowing just the change in kinetic energy, can we find the friction force and engine power?
I understand this topic well enough to get all the task done because they aren't very creative. But for my exam I think I should have this clear.
During the acceleration the force from the engine is ...
2
votes
1answer
287 views
Simple work and energy problem
I have the following problem:
A man that weights 50kg goes up running the stairs of a tower in Chicago that is 443m tall. What is the power measured in watts if he arrives at the top of the tower ...
1
vote
1answer
51 views
Maximum separation when 2 unlike charges shot apart
I want to compute the maximum separation when 2 unlike charges are shot apart from each other
...
1
vote
1answer
62 views
Basic energy calculation for N identical spin system
We have a system that has N identical spins $n_i$, and each spin can be in state 1 or 0. The overall energy for the system is $\epsilon\sum_{i=1}^{N}n_i$.
My understanding: There is only one ...
1
vote
1answer
259 views
Nuclear reaction: creation of deuterium
A proton p collides with a neutron(at rest) n at relatively low-energies and creates a 'deuterium-core' d:
p+n->d+γ
Find the wavelength for the photon as a function of the proton's momentum and the ...
1
vote
1answer
59 views
How to calculate the amout of time for oil to get out from a pneumatic cylinder?
I have a system. You can assume it is just a 1" diameter steel pneumatic cylinder (1 foot long). Assume we ignore the bore size issue at this point. One chamber is filled up by oil (6" of volume), ...
1
vote
1answer
108 views
Inefficiency Comparison of Car Air Conditioning vs. Open Windows
On a recent long, hot journey in Spain, I was pondering which was the most efficient way of cooling the car. Which of these would be the most effective?
Switching on the air conditioning, thereby ...
0
votes
1answer
34 views
Hamiltonion in 2-dimensions?
I am trying to construct a Hamiltonian for a system in 2 dimensions using Matlab.
I am not sure how this Hamiltonian will look like in matrix form.
If somebody can help me visualize this matrix that ...
0
votes
1answer
39 views
Composition of solar spectrum
I read some where that there are three types of UV and infrared rays namely UV-A, UV-B, UV-C and near infrared, mid infrared and far infrared. Which is the most abundant among the the three in ...
0
votes
1answer
81 views
Energy needed to lift and bring down an object
A mass of 0.5 Kg needs to be moved from point A to another point (B) which is 1 meters above point A. The time for this movement should be 0.2 seconds, then the mass is kept at position B for another ...
0
votes
1answer
46 views
What energy changes take place when you operate a jet-ski?
What energy changes take place when you operate a jet-ski?
0
votes
1answer
75 views
Simple harmonic oscillator system and changes in its total energy
Suppose I have a body of mass $M$ connected to a spring (which is connected to a vertical wall) with a stiffness coefficient of $k$ on some frictionless surface. The body oscillates from point $C$ to ...
0
votes
1answer
150 views
Definition of energy
What is the definition of energy $E$ given a dispersion relation $\omega=\omega(k)$ where $k=|\vec k|$ and $\omega$ is not necessarily linearly proportional to $k$? What about momentum $\vec p$?
This ...
0
votes
1answer
69 views
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas?
I think that you need work to preserve this process and you bring thermal ...
0
votes
1answer
205 views
How should I apply conservation of energy to this problem?
A block rests on a table. Then the block is pushed by a spring and slides across the table until it falls to the ground. The mass of the block is $1.30\text{ kg}$, the spring constant $550\text{ ...
0
votes
1answer
148 views
Calculating laser wavelength/power to cause emission of light in a gas?
It's been a long, long time since I've had to worry about electron excitation levels and band gaps. Please forgive (and correct!) my terminology and misconceptions. I've also posted this in the ...
-2
votes
1answer
82 views
Mathematical Modelling for Efficiency of PV thermal technology
As the efficiency of PV thermal or wind energy decreases with time(from the installment). Is there any mathematical model that gives its relation with time. i.e., whether it is a linear decrease or ...
5
votes
0answers
91 views
Positivity of Total Gravitational Energy in GR
I read the following statement in the introduction to an article:
Over the last 30 years, one of the greatest achievements in classical
general relativity has certainly been the proof of the ...
3
votes
0answers
47 views
How to convert Richter magnitude scale to approximate TNT?
I know the Richter magnitude scale is often used for measuring the strength of earthquakes. At the same time, explosive/destructive releases of energy are often quoted in equivalent amounts of TNT. Is ...
3
votes
0answers
103 views
Dirac action and conventions
I have a (possibly) fundamental question, which is driving me crazy.
Notation
When considering the Dirac action (say reading Peskin's book), one have
$\int ...
3
votes
0answers
267 views
How do I determine the Internal Energy of ammonia at a pressure in temperature when the steam table doesn't say it
I just bought a steam table for my thermodynamics class since they don't allow use to use the one from the book for the tests. This one is different from the one in my textbook as it doesn't give the ...
2
votes
0answers
56 views
The particle mesh ewald method in two dimensions
I am attempting to implement the particle mesh ewald method (http://dx.doi.org/10.1063/1.470117) in two dimensions. I am wondering what needs to be changed in the method from three dimensions to two ...
2
votes
0answers
69 views
Is there some connection between the Virial theorem and a least action principle?
Both involve some 'averaging' over energies (kinetic and potential) and make some prediction about their mean values. As far as the least action principles, one could think of them as saying that the ...
2
votes
0answers
251 views
kinetic energy in collisions
We were hoping you could help us understand collision energy.
Vehicle A is driving West at 35mph and weighs 1437kg.
Vehicle B is driving North at 35 mph and weighs 1882kg.
Vehicle B crashes into the ...
2
votes
0answers
373 views
Bungee jump physics
Question:
A bungee jumper jumps from a bridge. The length of the loose rope is 30 m. When the jumper reach the lowest point possible, the rope stretches 10 m. What is the final stretch of the rope, ...
1
vote
0answers
79 views
General physics question involving Heisenberg Uncertainty Principle
Question:
An unstable particle produced in a high-energy collision is measured to have an energy of $483\ \mathrm{MeV}$ and an uncertainty in energy of $84\ \mathrm{keV}$. Use the Heisenberg ...
1
vote
0answers
132 views
Potential energy of a spring
I have a little problem with the potential energy of a spring... I hope you can help me!
I have two coupled pendula, given by two masses $m$ fixed to two rigid bars (that haven't any mass) and with ...
1
vote
0answers
35 views
Any examples of negative ADM energy solutions with WEC but not DEC satisfied?
Any examples of negative ADM energy solutions with weak energy condition (WEC) but not dominant energy condition (DEC) satisfied?
Witten's proof of the positive energy theorem requires the dominant ...
1
vote
0answers
146 views
Slackline Jump Tension
So a slackline is basically a bouncy tight rope.
I found a site that has a calculator for the tension of a static slackline
...
1
vote
0answers
88 views
Is there analysis library for stress-strain data?
I have three column data that has time-displacement-force from 1D tensile/compression test. Now I would like to get the standard mechanical properties of the material, like Young modulus, yield ...
1
vote
0answers
166 views
Is the $mL_c$ value for triangular and rectangular fins the same value?
I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong.
...
1
vote
0answers
237 views
How equivalent are heat energy and work energy in connection with a spinning flywheel?
Let's say we have two identical spinning flywheels, that have arbitrary geometry, and are made of copper.
Now we apply some heat energy at the center point of flywheel A, causing it to slow down a ...
1
vote
0answers
242 views
Maxwell's Demon - laser cooling
There’s an interesting article on Scientific American
that tells how to cool individual atoms can bee cooled to within a very tiny fraction of Absolute Zero.
It uses two laser beams acting on a very ...
0
votes
0answers
27 views
Energy or Work done to pull an Iron cyclinder into a Solenoid
RadiI have been following the calcuations from these lecture slides here (slide 11). Where the slides attempt to approximate how much a solenoid pulls, by working out the energy required to pull an ...
0
votes
0answers
36 views
Time reversed laser
Recently, I read an article on time reversed laser. I don't know why they call it a time reversed. I have a doubt that why they use two laser in the device. And what is an anti-laser?
The device ...
0
votes
0answers
19 views
Tube light chokes away from the tube
I am going to fix 150 tubelights in a 17 X 12 ft room. To avoid heat generated warming of the room can I fix the chokes outside the rooms and connect to the tubes in the room? it will be almost25 ft ...
0
votes
0answers
19 views
Calculating population ratio for radiative transmissions in lasers
I'm trying to understand how the ratio of population is related to the energy gap between two energy levels. If an emission of a wavelength at 550nm is given off at room temperature (293K), then what ...
0
votes
0answers
93 views
Energy efficiency Vs power efficiency
I want to understand if there can be any real difference between the requirement of Energy efficiency and the requirement of power efficiency for a physical system. For example for CMOS-based digital ...
0
votes
0answers
247 views
Error Analysis, Change in momentum, Kinetic Energy
If momentum of an object is increased by 10%,then its kinetic energy will be increased by?
Well, I don't need the solution logically by calculating the change in Kinetic Energy etc, but my question ...
0
votes
0answers
86 views
Is this a possible scenario for the teleportation of energy?
Ok, so I've been reading a paper (Here's the paper) published by a physicist named M. Hotta et al. recently and as far as I can tell with my limited understanding, the protocol for the teleportation ...
0
votes
0answers
96 views
Simple: What do these ballistic impact numbers represent?
I bought physics for game programmers, found here, today to study ballistic impact, but I'm confused as to where a few numbers are coming from. I'm basically looking to understand what the values ...
0
votes
0answers
78 views
2 streams going into an engine and 2 come out. Find the enthalpy?
Problem: Steam supply to an engine is made of two streams that mix before entering the engine. Stream 1 flows at a $.01\frac{kg}{s}$ with an enthalpy of $2952\frac{kJ}{kg}$ and a velocity of ...
