Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright. Please READ THE GUIDANCE IN META before asking homework-like questions.

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0
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0answers
19 views

Finding Lagrangian with Non-holonomic constraints

I am stuck working on a problem that involves finding the Lagrangian for a free particle constrained to move on the surface of a disk of radius $a$. The particle collides elastically with the edge of ...
0
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1answer
21 views

What unit would the answer be in?

So I have used this formula: $$W= PV_1 \times \ln\frac{V_2}{V_1}$$ and I have converted my values to cubic meters and pascals. So Work Done, $W$, what would be the unit for that answer? I already ...
0
votes
1answer
18 views

Scale factor and energy density

I'm looking at some solutions of the Friedmann equation at this website: Solutions to Friedmann equation If I look at the first problem (Problem 1: matter or radiation in a flat Universe) and click ...
0
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0answers
24 views

Radially free falling observer

I am a student. i read in a paper for a radially free falling observer in a Schwarzschild metric, the relation between the Unruh vacuum state and the proper time was given as $$UH := \tau_0 −4\frac ...
-2
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0answers
17 views

How to write Laplace equation for this problem? [on hold]

How to write Laplace equation in below example. we have two plate with surface S,If we have charge surface density in boundary,obtain potential between two plate. explicitly explain for me how to ...
0
votes
0answers
11 views

Postion of a cylinder rolling down an inclined plane [on hold]

I know that the acceleration of a uniform cylinder of known mass rolling down an inclined plane WITHOUT slipping with an inclination of $\theta$ is: $\frac23 g \sin\theta$. Suppose this term is called ...
0
votes
0answers
34 views

Green function integration problem [on hold]

When I'm trying to find the Green Function of Helmholtz equation for a cube $0≤x,y,z≤L$ $$\nabla^2u+k^2u=\delta(\vec{x}-\vec{x}')$$ where $u=0$ on the surface. I set to find the green function where ...
-2
votes
0answers
19 views

Distanced covered when projected with escape velocity?

A body is projected from the center of the Earth with escape velocity, at what distance it will rise from the surface of the Earth? [Please do not give negative rating to my question. Tomorrow is my ...
1
vote
1answer
26 views

Finding the potential between two spherical shells [on hold]

How to find the potential in region $a<r<b$ I know that the general solution for Laplace's equation is $$V(r,\theta)=\sum_{l=0} \left[A_l r^l +\frac{B_l}{r^{l+1}} \right]P_l(\cos{\theta}).$$ ...
0
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0answers
19 views

Capillary action height

How to calculate height of the liquid (let's say it's water) in the capillary (so height of capillary action) if you only have r given, r = 0.3 mm - r is radius of capillary. The equation I would use ...
0
votes
0answers
12 views

Equal volumetric rate versus area open to flow [on hold]

A vertical water disposal well has been drilled and cased. There are two horizontal rock formations that the wellbore intersects and these formations will be targeted for water disposal. To allow ...
1
vote
0answers
24 views

vision problems [on hold]

While picking up a pair of eye glasses dropped by a friend, you notice that they form an inverted image of the background and that the image is stretched horizontally as well. Your friend suffers form ...
0
votes
1answer
26 views

Comparing voltages of Parallel and Series circuits

There are two electric circuits. Resistor 1 ($R_1$) connected with resistor 2 ($R_2$) by series circuit $R_1$ connected with $R_2$ in parallel Each of the circuit has battery with emf and the ...
0
votes
0answers
35 views

Inverse of a 3x3 matrix! I need some help! [migrated]

I have this 3x3 matrix $$E_{ij} = g_{ij} + \bar{\epsilon}_{ijk}z^k$$ and want to derive its inverse. I know that its inverse is given by $$(E^{-1})^{ij} = \frac{1}{1+z^2}(g^{ij} + z^{ij} - ...
-2
votes
1answer
35 views

Defining the Hamiltonian and obtaining equations of motion for physical system [on hold]

I have a relative simple mechanical system, that is modeled with 3 point masses and 3 links. There is an input force F working in the vertical direction and 2 torques $\tau_1$ and $\tau_2$. All ...
0
votes
0answers
22 views

Cohen Tannoudji solutions to exercises

Does anyone know where to find the solutions to the exercises of Cohen-Tannoudji's Quantum Mechanics? I am gonna try to do all of them and would like to check.
0
votes
0answers
21 views

Diameter of aluminium ring after it expands [on hold]

An aluminium ring has diameter $200.00$ mm at $25.00^0C$. What would be its diameter at $325.00^0C$? $\alpha$ for aluminium is $7.500 \times 10^{-5}K^{-1}$. Thanks for your help.
3
votes
0answers
39 views

Proving $[a_k^\dagger, a_q^\dagger]=0$

I am trying to prove the commutation relations between the creation and annihilation operators in field theory. I was already able to show that $[a_k, a_q^\dagger]=i\delta(k-q)$. I want to show that ...
1
vote
2answers
17 views

Understanding a graph of energy conservation with bounded and unbounded motions?

This graph is from the physics undergraduate text "Classical Mechanics by Douglas Gregory". Above this graph was the statement: What I didn't understand is- as stated in the under [*paragraph], ...
1
vote
0answers
26 views

Calculating rotation using moment of inertia [on hold]

I have an object A. I know its theoretical moment of inertia. I have a string wrapped around object A. I then apply a certain tension to that string, causing the object A to spin for a certain amount ...
0
votes
0answers
32 views

Time derivative of Magnetic Field as Source for Electric Field [on hold]

Show the following directly, and not by analogy with Ampere's law: $$ \vec E ( \vec r, t) = \frac{1}{4\pi} \int d^3r' \frac{(\vec r - \vec r')\times \frac{\partial \vec B (\vec r, t)}{\partial t} ...
1
vote
1answer
36 views

Equivalent tensor order parameters of nematic liquid crystals?

I found in the literatures two different definitions of the tensor order parameter of nematic liquid crystals. One is $$ Q_{ij}=\frac{S}{2}(3n_{i}n_{j}-\delta_{ij}), $$ where $S$ is the scalar order ...
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votes
0answers
13 views

Calculate the attenuation constant on a lossy transmission line [on hold]

$\nu$ = 10 [kHz] $L$ = 600 [nH/meter] $R$ = 50 [mOhm/meter] $C$ = 80 [pF/m] $G$ = 0 So the question on my test was what is $\alpha$, the attenuation constant? The answer is $\alpha$ = 0.25 [1/km] ...
1
vote
1answer
28 views

Fluid dynamics - immiscible liquids

Question: A U-tube of uniform cross-section is partially filled with a liquid I. Another liquid-II, which does not mix with liquid I is poured into one side. It is found that the liquid levels of the ...
0
votes
0answers
16 views

Capacitor energy density and power density, units conversion [on hold]

I would like to know how to calculate the energy density and the power density for capacitor using these 2 equations: $$ E \left(\rm\frac{Wh}{Kg}\right) = \frac18 \frac{\rm C\left(\rm ...
0
votes
0answers
52 views

What is the force required to move an object between two stationary objects? [on hold]

How would I determine the force required to move an object in the situation described below? There are a two sets of stationary components spaced apart equally and arranged in an array (as shown in ...
1
vote
0answers
23 views

Weight of a hemispherical bowl and a mass $m$ [on hold]

A particle of mass $m$ is A hemispherical bowl of mass M rests on a weighing scale. The inside surface of the bowl in frictionless. A particle of mass m is released from rest at the top of the bowl ...
0
votes
1answer
23 views

Problems with calculating Strontium-90 leakage due to Fukushima accident

Not long ago there was a spill of radioactive water at the Fukushima plants. Here are the data: $230 \times 10^6 \,\,\mathrm{Bq}$ of beta radiation are found in a liter of water. $t_{1/2} = 28.79 ...
0
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0answers
28 views

How to derive a new form of Hamiltonian operator in quantum mechanics using canonical commutation relation?

How does one derive $$\hat{H} = \frac{1}{2}\hat{p}^2m(\hat{q}) - \frac{i}{2}\hat{p}\frac{m'(\hat{q})}{m^2(\hat{q})} + V(\hat{q})$$ from hamiltonian $$\hat{H} = \hat{p}\frac{1}{2m(\hat{q})}\hat{p} + ...
0
votes
1answer
25 views

Separation distance of bright fringes in double slit experiment

so I'm working on homework problem that seems like it should be pretty straight forward but the computer won't accept my answer. The question is below. A double slit aperture with slit separation ...
0
votes
1answer
32 views

tangential acceleration and angular acceleration [on hold]

$$r= 2 \text{ m}$$ $$a_{\text{tangential}}=\frac{\pi}{4} \text{ m/s}^2$$ for half a turn What is the angular velocity from rest of the circular path? $$a_{\text{angular}} = ...
2
votes
1answer
44 views

Energy in harmonic oscillator [on hold]

The expectation value of the potential energy is exactly half the total according to Griffiths. Is that case always true for quantum harmonic oscillator? Is that the case also for classical harmonic ...
1
vote
1answer
25 views

Heat Transfer and Thermal Energy

Some hot water radiators have a single pipe connected to them. The steam comes to the radiator and the water leaves in the same pipe. The steam and the water are both at a temperature of 100°C. Where ...
3
votes
1answer
96 views

1D Finite potential well: solutions with $\sinh$ and $\cosh$?

So I am studying the (one dimensional) quantum mechanical finite potential well defined by: $$ V(x) = \cases{0, &|x|>a\cr -V_0, &|x|<a} $$ where $V_0>0$ is a real number. I know ...
0
votes
1answer
69 views

Difference between a hydrogen ion and a proton

I've run into a bit of a problem on this weeks coursework. A proton and an electron initially at rest combine to form hydrogen. Find the wavelength of the emitted photon? So, as far as I can ...
1
vote
0answers
31 views

Finding conserved quantities from Hamiltonian when Symmetry is not evident [on hold]

A particle is moving in 3D space, under a potential $$V = -\frac{\alpha}{r}-\frac{\vec{r} \cdot \vec{\mu}}{r^3 } $$ where $\vec{\mu}$ is some constant vector. I need to show there are three ...
-2
votes
2answers
30 views

What does $\tau$ = $\Delta E_{c}$ mean? [on hold]

What does $\tau$ = $\Delta E_c$ mean? Can anyone help? I'm finding it difficult to find on the internet.
0
votes
1answer
56 views

Pushing over a block [on hold]

Consider a rectangular block of mass $m$ and uniform density resting on a frictionless surface. The height is $h$, the width $w$, the length $l$. Consider one of the faces with dimmensions $l$ by $h$. ...
0
votes
2answers
52 views

Forces and acceleration on rotating objects?

Suppose you have an object undergoing uniform circular motion, with force vector pointing towards the center and another force vector tangential. Can it be said that the net force pointing in the ...
1
vote
1answer
107 views

Deriving a Useful Solution of the Schrödinger Equation [on hold]

How does one derive the fact that $$\psi(t,x) = (\tfrac{2 \pi \hbar t}{m})^{-d/2}\int_{\mathbb{R}^d} e^{im\tfrac{(x-y)^2}{2\hbar t}}\psi_0(y)dy$$ is a solution of the time-dependent Schrödinger ...
-1
votes
0answers
27 views

Stuck on Snell's Law [on hold]

I'm currently studying triple science at GCSE level and we have just learned Snell's Law. I have been given homework on the topic, but I'm a little bit confused as to when I used sin, inverse sin, ...
3
votes
3answers
593 views

Should a Gaussian Curve Always Be Drawn Symmetrically?

This question is more about the appearance of a curve that comes up while I am analysing my data rather than an actual physics question, but I think it's relevant. I have analysed some data from an ...
-1
votes
1answer
30 views

Find the impulse momentum [on hold]

A boy of weight 40 kg stands on a board of weight 60 kg. The board is on ice (friction force =0): Find the velocity of the movement of the boy and the board when he moves from one side to another.
0
votes
0answers
18 views

Convert this to a Hamiltonian system and find Hamiltonian [on hold]

I tried solving this by using the conjugate momentum and position formulae: but could not get the answer. EDIT: I have used the same procedure as mentioned in this Phys.SE answer but the ...
0
votes
0answers
48 views

Help with my schoolwork [on hold]

I have to do project about Newton's Movement Laws, and I decided to write about the situations, where do NML not work. For example, why does photon have force and momentum, when it has 0 mass. It's ...
0
votes
0answers
73 views

By what force does a man attract Earth? [on hold]

By what force does a man attract Earth? a) 800N b) 80N c) he doesn't attract it By putting some values into the formula for gravitation force I get about 785N. Is it (a) then?
-2
votes
0answers
8 views

Solving for initial velocity required to launch a projectile to a given destination at a same height formula [on hold]

with the premise that gravity (gravity is 10m/s) is the only force acting on it after initial launch (no air friction) the angle is 30 deg and the destination is 40 meters
0
votes
0answers
21 views

Ames Room, how to construct properly?

I have been assigned to create an Ame's Room for a physics project. However, the teacher told us very little about it, and wanted us to figure it out through trial and error. Today I spend 6 ...
0
votes
0answers
9 views

Transistor Series Regulator [migrated]

I am in the 6th week in Navy school and we are on voltage regulators or circuits that have components that maintain a constant voltage output. I need an explanation on how to work out this problem ...
1
vote
2answers
198 views

Triple integral $\iiint_{\mathbb{R}^3} d^{3}q ~\delta^{3}(\vec{q})\frac{(\vec{p}\cdot\vec{q})^2}{q^{2}} $ involving Dirac Delta function

I am trying find $$\iiint_{\mathbb{R}^3} d^{3}q ~\delta^{3}(\vec{q})\frac{(\vec{p}\cdot\vec{q})^2}{q^{2}},$$ where $\vec{p}$ is some fixed vector. The answer should be $\frac{p^2}{3}$. Below is ...