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1answer
78 views

Distance for No Quantum Effects Between Two Wires

Two wire traces on a substrate are separated by a distance d. Each wire carries a current. The mean energy of the electrons in the wires is E. Estimate the minimum distance that must exist between the ...
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1answer
51 views

Force experienced on two particles in a rotating system?

I've a system of two particles of the same mass who rotate in a circle about the centre of mass of the two particles. Is the force experienced by the particles $F=MV^{2}/r$ or should I use ...
1
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1answer
74 views

How would you quantify and predict the internal friction and efficiency of a bungee cord?

I am in an introductory physics class and we have been working with Gravitational Potential Energy, Elastic Potential Energy, Kinetic Energy and the Law of Conservation of Energy in relation to bungee ...
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1answer
61 views

friction between 2 bodies [closed]

There is a plank on which a block is kept. the block is given some velocity. Now if there is friction between block and plank it will act opposite to it's velocity for sure. but the plank is free to ...
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1answer
41 views

Determining distance from object in concave lens [closed]

so I was studying for my Yr11 Physics test tomorrow and I came across a question that I got the wrong answer on, all of my friends are getting the same answer. Question: You wish to project the image ...
3
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0answers
438 views

Adiabatic expansion in van der Waals gas

Given a Van der Waals gas with state equation: $$\left( P+\frac{N^2 a}{V^2}\right)\left( V-Nb \right)=NkT,$$ show that the equation of an adiabatic process is: $$\left( ...
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0answers
74 views

Buoyancy Correction for a Kater Pendulum

Question: Consider a Kater pendulum: that is, a rod with two cylindrical masses at both ends, with a knife edge between the two masses and another between one ...
8
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3answers
107 views

Correct expression for experimental data

I am doing practices at the laboratory. I have some doubts about how to express correctly the errors; I read some pdfs in Google but I can't solve these questions: Sometimes, it's correct to write ...
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2answers
356 views

Fluid Mechanics Piston Problem

The actual problem: A hydraulic car lift has a reservoir of fluid connected to two cylindrical fluid filled pipes. The pipe directly below the car has a diameter of 1.8 m. the pipe on which the ...
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2answers
139 views

Determining the neutral axis of an I-shaped cross section with dissimilar materials

Determine the neutral axis of the I- shaped cross section with dissimilar materials. The top rectangle of the cross section is made out of aluminum and the second and third part are titanium ( these ...
3
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1answer
96 views

Retarded (Advanced) GreenFunction [closed]

I need to show that Green Function: $\displaystyle G(\vec{r},t;\vec{r}^{\prime},t^{\prime}) = \frac{\delta(t-t^{\prime}\pm |\vec{r}-\vec{r}^{\prime}|\,/c)}{|\vec{r}-\vec{r}^{\prime}|}$ Obeys ...
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1answer
32 views

Want to achieve maximum magnetic force & find out the max point [closed]

Hi Sir/ Madam Want to achieve maximum magnetic force & find out the max point for this setting, want to know is the strongest magnetic force must in the 'dot' area ( middle poin of setting ) ...
1
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1answer
59 views

Commutator evolution operator and position operator

Let $H= \frac{p^2}{2m}$, then I am supposed to calculate $[x,e^{-iHt}]$. My idea was to use $[x,p^n]=i \hbar n p^{n-1}$ and so I ended up by using the series for the exponential function with ...
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votes
1answer
340 views

Poisson's equation with a point charge source [closed]

How do you derive the solution to Poisson's equation with a point charge source? Without using Coulomb's law or the electric field! To be more explicit, we have a point charge at $(0,0)$ of charge $q$ ...
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0answers
80 views

Characteristic length of differential element of cylinder surface?

I am trying to find the Nusselt number for a small element of the outside of a cylinder that has a height of $Delta z$. I found the average Grashof number of a surface as $$Gr_{L}=\frac{\beta \rho ...
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0answers
71 views

Finding kinetic friction coefficient

A box is thrown up an incline with degree $\alpha$. the kinetic-friction coefficient is $\mu_k$. the body returns back to its start point. a. prove ...
5
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1answer
225 views

How do I measure the spin along an arbitrary direction?

I need to measure the atoms spin along a direction perpendicular to the z-axis but at an angle $$ \phi $$ with the x-axis. They then get the output of the spin measured is + with probability $$ ...
-2
votes
1answer
54 views

What distance has the soldier travelled? [closed]

A troop $5$ meters long starts marching. A soldier at the end of the file steps out and starts marching forward at a higher speed. On reaching the head of the column, he immediately turns around ...
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1answer
38 views

Scalar Field of a long thin wire

Given the situation that $B=-\nabla A$ where B is magnetic field and A is some Scalar Field. How can I calculate the scalar field, A. We are dealing with current free region, here. I know we can ...
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0answers
62 views

How to relate compression ratio to work input for a compressor in a heat pump

So I need to calculate the COP (Coefficient of Performance) for a 6-ton air conditioner system in terms of the compression ratio. I understand that: $$COP=\frac{Q_L}{W_{net,in}}$$ I cannot find out ...
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2answers
76 views

Classical Mechanics - Allowed systems

I've edited my question to clear any possible confusing parts: This an exercise from the book "The Theoretical minimum", I'm paraphrasing. In classical mechanics, dynamical laws must be reversible ...
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3answers
307 views

Archimedes' principle for two liquid layers

Problem: I have a cylindrical vessel of height $H$ and radius $R$. There are two liquid layers in the vessel. The first has density $D_1$ and height $h_1$, the second has density $D_2$ and height ...
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2answers
229 views

Conservation of Angular Momentum and linear velocity

I have a problem where a cylinder is moving on a horizontal surface, starting with velocity $v_0$. It is given that its radius is $10\text{cm}$, its mass is $200\text g$ and the coefficient of ...
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2answers
65 views

How many years would it take the Pioneer space probe to travel to Proxima Centauri with its current speed? [closed]

Pioneer space probe moving at a speed of $30km/s$. Assuming its heading for Proxima Centauri, which is situated at $4.2ly$ from earth, calculate how long it would take to get there in years, to the ...
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0answers
186 views

The commutator of scalar field [closed]

I have a real scalar field which is given by the propagator as: $$[\phi(x),\phi(y) ] =\int \frac{d^3 p}{(2\pi)^3} \frac{1}{2E_0} (\exp(-ip\cdot (x-y)) -\exp (ip\cdot (x-y)))$$ And I am asked to show ...
1
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1answer
32 views

Molecular formula of a compund [closed]

I have no idea on how to get information out of this one. A compound contains only hydrogen and nitrogen. Nitrogen makes up for 87.4% of the mass. A sample of this have a density of 0.977 g/L at ...
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1answer
161 views

Spinors and Probabilities of Electron-Positron Pair

Question: An electron and positron are moving in opposite directions, and are in the spin singlet state. Two Stern-Gerlach machines are orientated in some ...
3
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2answers
91 views

Smallest number of quantum gates to simulate other gates?

What is the smallest number of Fredkin gates needed to simulate a Toffoli gate? What is the smallest number of Toffoli gates needed to simulate a Fredkin gate? Where the Toffoli's gate is the CCNOT ...
2
votes
2answers
92 views

Relative velocities of boats and a stone thrown by the boat [closed]

Question: A police boat is chasing a boat with criminals along a straight river by moving against the stream. The speed of the river stream is 3 miles per hour, the speed of the boat with ...
1
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1answer
332 views

Newton's second law, gravity and buoyancy [closed]

A body of mass $m$ and volume $V$ is immersed into the sea. The body moves under the action of two forces: gravity and buoyancy (Archimedes). Gravity force has a magnitude $mg$, where $g$ is a ...
2
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0answers
263 views

Radial Wave Function for Spherical Squared Well Potential and $S$-Matrix

I have a problem with this exercise because I really don't know how to proceed. It's related with the "S-matrix". In class we saw this example: Consider the spherically symmetric potential: ...
2
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1answer
43 views

A question about verifying the transverse of electric field

I came accross a question about verifying the transverse of electric field in Peskin and Schroeder's QFT p179. Given $$ \mathcal{A}^{\mu}(\mathbf{k}) = \frac{ -e}{| \mathbf{k} | } \left( ...
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2answers
123 views

How to derive inverse Fourier transform for periodic functions (in crystal lattice)?

I would like to derive the following two well-known formulas that work for crystal lattice [1]: $$ F[f(\mathbf{x})] \equiv \tilde f(\mathbf{G}) = {1\over\Omega_\mathrm{cell}} ...
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1answer
59 views

Homework - Mechanics [closed]

Just started mechanics and I'm not sure what I'm doing wrong on a question. Car accelerates uniformly from a speed of $50\: \mathrm{kmh}^{-1}$ to a speed of $80\: \mathrm{kmh}^{-1}$ in $20$ ...
3
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0answers
55 views

Normal ordening with gamma matrices and fermions

I'm dealing with a normal ordered product of the form $$:\overline{\psi}(x_1)\gamma_\mu A^\mu(x_1)P[{\psi(x_1)\overline{\psi}(x_2)}]\gamma_\nu A^\nu(x_2)\psi(x_2): $$ where $P[\cdots]$ indicates a ...
3
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3answers
169 views

In the static spacetime, the extrinsic curvature of hypersurface $t=constant$ is zero

How can I prove that in the static spacetime, the extrinsic curvature of hypersurface $t=constant$ is zero? My efforts all are failed. Any hint would be greatly appreciated.
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1answer
176 views

Use kirchhoff's second law to deduce the resistance R of the resistor [closed]

Using what I learned so far, i constructed an equation like this: $$30V=(I_{1}\times 20\Omega)+10V+(0.2A\times 10\Omega)+(I _{3}\times 10\Omega)+(0.5A\times R)$$ Which is clearly not solvable on ...
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0answers
57 views

Some strange transformation [closed]

In a lecture (look at the chapter "The fermion determinant in a constant field", p. 5) I found some strange transformation, which is given by eq. 18. How to prove it? Exactly, I don't understand the ...
0
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1answer
84 views

Integration with Grassmann variables

How to show that $$ \int d\Psi d\bar {\Psi}e^{i \int d^{4}x\bar {\Psi} \hat {A} \Psi} = det (\hat {A})? $$ $\Psi , \bar {\Psi}$ refers to Dirac spinors (the second is $\bar {\Psi} = ...
7
votes
1answer
239 views

Is there any usage of $x^x$ in physics? [closed]

I am so excited about the function: $x^x$. I would like to know if there is any usage in the physics world of this function. Is there any formula that uses $x^x$?
3
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2answers
84 views

Work and energy problem [closed]

I am trying to solve the problem (see image), my concern is about the 2 factor, can anyone please help me understand this.
0
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1answer
102 views

E&M question in example in my book [closed]

So I still not sure how to apply like Right-hand rule (RHR) in this setup in problem like the one in the following so I tried to do RHR in order to get the direction but it didn't work out. This is an ...
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2answers
91 views

Relative velocity of boat

I am trying to understand fully the following question: A boat is traveling west at 100m/s and is partially helped by a strong wind blowing at 20m/s 30 degrees north of west. What speed could the ...
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0answers
130 views

The formation of ice from water properties? [closed]

The formation of ice from water is accompanied by: A. absorption of energy as heat B. temperature increase C. decrease in volume D. an evolution of heat E. temperature ...
3
votes
1answer
56 views

Mean kinetic energy according to the WKB approximation

Show that in the WKB approximation, the mean kinetic energy $T_{n1}$ in a bound state $\psi_n$ in a potential $V(x)$ is given by $\langle T_n \rangle = \frac{1}{2}\left(n+\frac{1}{2}\right) ...
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0answers
33 views

Help with inductance and a moving (rolling) rail problem

I can't even do the first part. I've exhausted just about every direction. I've done plenty of moving rail problems without rolling, but I'm guessing you have to have some relationship between the ...
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1answer
132 views

Missing centrifugal acceleration

I am trying to get correct equations for acceleration of a point in reference frame A, given position, velocity and acceleration in rotating reference frame B. Let $\mathbf{x}_A(t)$, ...
2
votes
2answers
152 views

Peskin and Schroeder Equation 3.23

I've been trying (for a while) to prove that $S^{\mu\nu}:=\frac{i}{4}\left[\gamma^\mu,\,\gamma^\nu\right]$ is a representation of the Lorentz Lie algebra, that is, to prove that it satisfies the ...
2
votes
1answer
103 views

How long would it take a projectile accelerating twice as fast as another to catch up?

Given a projectile with initial velocity $u$, and constant acceleration $a$, travelling in the one direction. How long would it take a second projectile the same as the first with the same initial ...
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3answers
153 views

Effect of incoming force on linear vs. angular velocity

First of all, I should note that I'm a programmer and have only an extremely basic understanding of physics; I only know how to explain my question in layman's terms and I apologize if I'm unclear or ...