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How to determine the speed and acceleration of an item moving vertically when another item moves horizontally? [closed]

A horse lifts a bucket with a rope and a pulley. Find the velocity $v_{a}(x)$ and acceleration $a_{A}(x)$ in terms of $x$. How do I go about solving this? What is wrong in my attempt?
Delta Foxtrot's user avatar
0 votes
0 answers
55 views

Eigensystem of part of the representation of the position operator: $a^\dagger+a$ in the base of the quantum harmonic oscillator [closed]

What are the exact eigenvalues and eigenvectors of the following matrix? \begin{equation} \begin{pmatrix} 0&\sqrt{n}&0&\cdots&0&0\\ \sqrt{n}&0&\sqrt{n+1}&\cdots&0&...
Thanos Athanasopoulos's user avatar
7 votes
1 answer
641 views

Photon propagator in path integral vs. operator formalism

I am self-studying the book "Quantum field theory and the standard model" by Schwartz, and I am really confused about the derivation of the Photon propagator on page 128-129. He starts ...
Andrea's user avatar
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0 votes
0 answers
10 views

Modeling centrifugal distortion with an effective charge distribution

The hamiltonian of a rigid object with a totally symmetric moment of inertia (i.e. a "spherical top") will depend only on the magnitude of its angular momentum. If we allow the object to ...
creillyucla's user avatar
0 votes
2 answers
56 views

Some questions regarding a pulley [closed]

Please have a look at the following diagram sketched by my Professor. The points $P_1$ and $P_2$ have mass $m_1$ and $m_2$ respectively . The pulley is frictionless and it is represented by a ...
Davide Masi's user avatar
-4 votes
1 answer
64 views

As I read an article on this website that light cannot warp space time fabric [closed]

But actually we know that energy is equals to mass then light energy can act like mass and it can create a black hole made up of light . As per Einstein equation E=mc² then why there is no black hole ...
Arpit Jha's user avatar
0 votes
6 answers
144 views

Why won't there be any transfer of heat energy when ice at 0°C is in contact with water at 0°C in a closed container?

In my book, Concise Physics of Selina Publications for Class IX, it's written there that "If there is no transfer of heat between the two bodies placed in contact, they are said to be at the same ...
Kakiaririki's user avatar
0 votes
1 answer
36 views

How does Shear Force on a fluid in a vessel reaches an equilibrium if molecules are free to make contact?

In Hydrostatic, if the fluid is a perfect fluid that is non-viscous, it doesn't experience any shear force because if it would experience so it might start flowing so something might be working to ...
soumyadip_poddar's user avatar
0 votes
2 answers
47 views

Why the frequency component is not included when the energy of a wave is described?

Energy of a wave is directly proportional to its Amplitude squared. There is no inclusion of frequency in it. But by intuition if one thinks about it, isn't it obvious that a wave with higher ...
Vibhav shivadeker's user avatar
3 votes
1 answer
354 views

From what equations is magnetic field uniquely determined for a given current distribution?

The Maxwell equations for magnetostatics in the absence of time varying electric field state that - $$ \mathbf{\overrightarrow{\nabla}} \cdot \mathbf{\overrightarrow{B}} = 0 $$ $$ \mathbf{\...
Bipul Kumar's user avatar
1 vote
1 answer
69 views

Mapping between generalized forces and external torque of a rigid body whose rotation is described by quaternion is not unique(?)

In this paper the mapping between generalized forces and external torques for a rigid body (when the rotation is described by a quaternion) is derived: $$\textit{F}_Q = 2\textbf{G}^TT'$$ where $\...
blenderman's user avatar
0 votes
0 answers
23 views

Find the tension in the string when the string is vertical [closed]

By using Work Energy Theorem, as well as Velocity of centre of mass, I succeeded in finding the velocities of both the ring as well as block. I noticed that there is going to be a vertical circular ...
Science Tard's user avatar
1 vote
0 answers
55 views

Theoretical explanation on calculating magnetic moment of materials in quantum mechanics [closed]

Could someone please provide a comprehensive and in detail theoretical explanation of how to calculates the magnetic moment of a material(total magnetic moment and absolute magnetic moment) of a ...
Thejan Hasaranga's user avatar
-1 votes
0 answers
16 views

Distance traveled by a ball in a rotating rod [closed]

I have a mechanism here. there is a ball with mass m in a rod with mass M that it is pinned from one side, we release the rod, so it rotates. at the time when the rod is vertical, the ball has ...
Miumen's user avatar
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2 votes
2 answers
56 views

Is First-Class Constraint Generator of matter Gauge Symmetry in EM example?

In EM theory, we can find first-class primary constraint, $$\Pi^{0}(x) = 0\tag{1}$$ and first-class secondary constraint, $$\partial_{i} \Pi^{i}(x) = 0\tag{2}$$ with Lagrangian $$\mathcal{L} = -(1/4)F^...
Ting-Kai Hsu's user avatar
0 votes
0 answers
21 views

Magnetic Dipole Derivation

$\oint (\hat{r}\cdot \vec{r}') d\vec{l} $ is what I get as part of the magnetic dipole term, but I can reduce this to $ -\vec{r}' \times \int d\vec{a}' $. I don't understand how you can reduce it to ...
ram nikash's user avatar
2 votes
1 answer
58 views

Bohmian mechanics, Leggett inequality, realism and nonlocality

Very often it is said that the Bell inequality has ruled out the possibility of hidden variables (HV) in QM. This is incorrect since Bell inequality has ruled out local hidden variables: nonlocal HV ...
truebaran's user avatar
  • 283
0 votes
0 answers
76 views

End points of event horizon

I am reading The Nature of Space and Time by S. W. Hawking. In the last paragraph on page 16 he said that: event horizon may have past end points but don't have any future end points I understand ...
Talha Ahmed's user avatar
1 vote
1 answer
58 views

Defining the geometry of Bell inequalities

Bell inequalities can be discussed in the language of geometry. In papers such as [1], there is a general flow of definitions leading to the geometric picture of Bell inequalities: $$\text{Behaviors} \...
Silly Goose's user avatar
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0 votes
1 answer
34 views

Drawbacks of Quasi-Static process for lifting a block

Definition of Quasi-static: A quasi-static process is a thermodynamic or mechanical process that occurs very slowly, allowing the system to remain in a state of equilibrium at all times. While ...
Akhilesh G's user avatar
0 votes
0 answers
24 views

Voltage biased Josephson junction

In his lecture notes on circuit QED, Girvin writes the hamiltonian of a Josephson junction with a voltage bias $V$ (ignoring the Coulomb interaction) as $$H = H_{T} + U$$ where $$H_{T} = -E_{J} \...
Ric's user avatar
  • 113
0 votes
1 answer
51 views

Clarification of Weinberg's cosmology book eqns 5.1.44-5.1.47 for scalar perturbation

Has anyone clarified the equations in Weinberg's cosmology book for scalar perturbation for nonzero $F$ and $B$, eqns 5.1.44-5.1.47. I am not sure why there are terms with $\nabla^2 \dot{B}$ and $\...
Shiv's user avatar
  • 1
-1 votes
0 answers
47 views

Probabilistic curvature of spacetime [duplicate]

I was wondering since matter tells space-time how to curve, and since matter is probabilistic in position (say hydrogen atom) is the curvature also probabilistic? black holes slowly shrink by ...
Mantu Das's user avatar
1 vote
1 answer
52 views

Can plasmas have eddy currents?

A couple days ago I asked a question on if plasma could have a magnetic field due to current which was a yes. Now I am wondering again on if plasma can possess eddy currents. Assuming a time varying ...
Coolcats112's user avatar
0 votes
0 answers
18 views

Pressure build inside water tank [closed]

It‘s been a few years since I had my last physics class so please be kind to me. I came here to ask you about a phenomenon I recently discovered in a design of mine. The object in question is a stand ...
saeppi's user avatar
  • 101
0 votes
0 answers
62 views

Does the SailBeam concept violate conservation of etendue?

SailBeam is a proposed method of spacecraft propulsion based on laser-driven sails. The SailBeam laser pushes on a series of "microsails," each sail having around 0.1m radius. Each microsail ...
causative's user avatar
  • 910
5 votes
2 answers
1k views

Why can we treat a ball as a point mass to calculate torque?

A sphere of radius $R$ is supported by a rope attached to a wall as shown in the below figure. The rope makes an angle $\theta$ with respect to the wall. The point where the rope is attached to the ...
Ryder Bergerud's user avatar
0 votes
0 answers
37 views

Help with understanding continuum model [closed]

I need some feedback on my thought process regarding the continuum model. So before thinking about what a density field, specifically density at a point, meant in 3D, I began with 1D. What came to ...
JustBao's user avatar
  • 11
0 votes
2 answers
45 views

How can both angular displacement and angular distance share similar equations?

Equation for finding angular displacement is: $$ d\vec{\theta} = \vec{\omega} dt$$ In the case of rotational motion with constant acceleration, we can use the following equation for angular velocity: $...
Alexander Djurovich's user avatar
0 votes
1 answer
57 views

Could a single gamma ray photon break the Schwinger limit? If so, at what energy?

Is it possible for a ray of light, or even a single photon, to 'break' the vacuum of space? If so, at what energies (in eV, e.g.) would this happen?
Kurt Hikes's user avatar
  • 4,509
-1 votes
0 answers
75 views

Is there a straightforward simplified proof of energy conservation from time translation symmetry?

Electric charge conservation is easily proven from electric potential gauge symmetry, as follows: The potential energy of an electric charge is proportional to the electric potential at its location. ...
Stack Exchange Supports Israel's user avatar
-4 votes
1 answer
69 views

Is my simplified explanation of Volts vs Current correct? [closed]

I was struggling to find any meaningful difference between Volts and Current, when studying the basics of Ohm's law. The sentences explaining Potential Difference, between the negative and positive ...
securityauditor's user avatar
-1 votes
0 answers
54 views

What would be the displacement-time graph for a body dropped from a certain height which bounces back to the same height after hitting a surface? [closed]

For a freely falling object, displacement-time graph looks like this: When we observe the motion of a ball thrown upwards, the graph looks like this: When the ball moves upwards retardation occurs ...
Kakiaririki's user avatar
2 votes
2 answers
136 views

When is the Lagrangian a Lorentz scalar?

The Lagrangian $\mathcal{L}$ can be defined as the Legendre transform (when it exists) of the Hamiltonian $\mathcal{H}$, a non-Lorentz scalar quantity (as $\mathcal{H} =T^{00}$). My questions are, ...
Gabriel Ybarra Marcaida's user avatar
1 vote
0 answers
22 views

Connection between dispersion relation and symmetries of the Hamiltonian

I am having trouble understanding intuitively the connection between the dispersion relation and the symmetries of the Hamiltonian. For example, suppose we have a lattice and there are four sub-...
JosephSanders's user avatar
1 vote
0 answers
39 views

Does electric and magnetic field from electromagnetic radiation are 2D based? [closed]

I'm getting into physics, specially in electromagnetism. When we're talking about electromagnetic radiation. Does it has a 2D shape when it's propagating through space? Does Maxwell's equations ...
Psi's user avatar
  • 11
-2 votes
0 answers
48 views

Magnetic Field Generation in a Vacuum Through Special Relativity

The way special relativity explains electromagnetism is that when electrons move, their lengths contract due to relativistic effects, even though they do not move at extremely high speeds. This ...
Gopal Kaushik's user avatar
0 votes
0 answers
32 views

Calculating Binding Energy of Th 230 nucleus [duplicate]

Ok this is NOT a homework question. But it’s somewhat related. Please bear with me. In calculating BE of Th 230, I used the rest mass of proton as 1.007276u and rest mass of neutron as 1.008665u (as ...
esdoublelef's user avatar
6 votes
5 answers
4k views

Wikipedia states that the relativistic Doppler effect is the same whether it is the source or the receiver that is stationary. Can this be true?

According to Wikipedia, the relativistic Doppler effect is simply the classical Doppler effect for a stationary source, $1-v/c$, times the relativistic time dilation, $1/\sqrt{1-v^2/c^2}$ (where v is ...
John Hobson's user avatar
0 votes
0 answers
29 views

Question regarding friction acting on a disk on a conveyor belt [closed]

I have the following problem on which i am working A horizontal conveyor belt is running at a constant speed of $v_b = 3.0\hspace{1mm}m/s$. A small disc enter the belt moving horizontally with a ...
Hhh Hhh's user avatar
2 votes
1 answer
66 views

Time evolution of state in first and second quantization

I was trying to work out the time evolution of a single particle state in second quantization and got something apparently contradicting with the first quantized picture. For a system with energy ...
Rupert's user avatar
  • 29
0 votes
1 answer
47 views

Strogatz's condition on definition of energy

In, Nonlinear Dynamics And Chaos, 2nd edition page 160, by Steven H. Strogatz, he writes Let’s be a bit more general and precise. Given a system $$\dot x =f(x),$$ a conserved quantity is a real-...
GedankenExperimentalist's user avatar
0 votes
0 answers
22 views

Calculating tension in a pressurized container [closed]

Suppose I have a pressurized spherical container made of 1 mm thick aluminum. The container has pressure P and internal volume V. How would I calculate the tension in the aluminum? The aim of this is ...
Varshil MVH Pets's user avatar
0 votes
1 answer
82 views

Why Consider Only Triplet States for Spin in $2$-Electron Systems?

I have a question regarding systems of 2 electrons and their spin properties. When the Hamiltonian of a system of 2 electrons can be written as a sum of two single-particle Hamiltonians that are ...
SimoBartz's user avatar
  • 1,904
-4 votes
0 answers
55 views

What is Suvrat Raju's point of view towards information paradox? Is it accepted by others? [closed]

Wondering what's the gist of his idea https://arxiv.org/abs/2012.05770 https://www.suvratraju.net/classes/black-hole-information-paradox/materials/lecture-1-introduction-and-two-point-qft-cor
Helen's user avatar
  • 1
0 votes
0 answers
36 views

Field theories where the potential solves a linear Schrodinger equation

Are there physical situations/applications where the potential solves a linear time-dependent Schrodinger equation, or where the gradient of a solution to the Schrodinger equation (after somehow ...
kieransquared's user avatar
0 votes
0 answers
37 views

Pressure at a point around the corner in a conical fask [duplicate]

I have gone through this two very informative links in understanding pressure. Weight of fluid in a conical container act entirely on the base? Pressure is isotropic But in a long conical flask which ...
soumyadip_poddar's user avatar
1 vote
1 answer
86 views

Do Helium-4 atoms behave like photons?

I know that the Helium-4 atom is a boson. Does this mean that, like photons, many Helium-4 atoms can be placed at the same point in space? How its possible? It includes fermions (Protons, Neutrons, ...
reza's user avatar
  • 209
0 votes
0 answers
8 views

Finding out the number of minima for a fourier expansion [migrated]

Suppose I have a Fourier series f(x) = $\sum_{n=1}^N t_n cos(nx)$ defined in the domain $(-\pi,\pi]$. we need to prove that mathematically we can ' at most' have N minima points excluding the boundary ...
ANIMESH GHOSH's user avatar
0 votes
1 answer
47 views

Calculating the expectation value of the angular momentum operator

I'm not looking for the exact answer to the question, but rather why a certain way of solving it is chosen. We agree on the answer, but why is the approach different. I'm afraid it's a sign of me not ...
Rommelaar's user avatar

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