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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0answers
10 views

what force pump is needed to power

Im studying design have not got a good grasp on maths, but understand the working principles of pressure and water! my problem hopefully has included all necessary info in the image. Please help. ...
0
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0answers
7 views

Resultant forces on system of particle is zero , we can have?

This is how the specific question is framed? If the resultant of all the external forces acting on a system of particles is zero, then from an inertial frame, one can surely say that: 1: ...
0
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0answers
15 views

Relation between Fourier Transform of potential $v(x)$ and |r| in Born approximation

I'm doing an exercise about Kronnig Penny model and I'm asked to do the following: If $t=|t|e^{i\delta}$ and $r=\pm i|r|e^{i\delta}$ are respectively the transmission and reflection coefficients. And ...
0
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2answers
43 views

Charging a capacitor using a capacitor?

I recently did an experiment using a fully charged capacitor (assumed) and charged a separate capacitor through fixed resistor. We measured the potential difference of the capacitor being charged. We ...
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0answers
7 views

Polarization vector in 2+1 D

I solved eq. $-\partial^2 A^\nu + M \epsilon^{\nu\rho\sigma}\partial_\rho A_\sigma=0$ to find $\epsilon^\nu(k)$ Where $A^\nu= \epsilon^\nu(k) e^{ik\cdot x}$ and $ \nu=0,1,2$ (2+1 D case) and ...
2
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2answers
16 views

Formula for balance with three arms?

I'm searching for a way to express the angle of the arm of a balance instrument expressed in the weight that is present in one arm. For a two legged balance one could use the moment formula: moment = ...
0
votes
1answer
29 views

Quantum Physics - What is the probability of it being in specific state (Stuck on question)

The normalised wavefunction for an electron in an infinite 1D potential well of length 65 pm can be written: $$\psi=(0.038 \psi_{n=1})+(-0.227\ i \psi_{n=10})+(g \psi_{n=5})$$. If the state is ...
0
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0answers
20 views

Penrose diagram for Schwarzschild metric

Can someone show me a procedure (I mean a complete series of mathematical passages) to derive the Penrose diagram for Schwarzschild metric? I don't want to do that passing through the Kruskal-Szekeres ...
0
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1answer
14 views

Trick for reformulating in terms of centre of mass and relative variables

I am working through a problem that has caused me difficulties in the past. I have the Hamiltonian $$\mathcal{H}=\frac{p_1^2}{2m_1}+\frac{p_2^2}{2m_2}+\frac{k}{2}(q_1-q_2)^2$$ I want to express the ...
0
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0answers
17 views

Scarlar Yukawa theory derivation

I am using Tong's notes for QFT, and on page 59 there is a derivation for the scattering amplitude of $\psi\psi \rightarrow \psi\psi$ in Scalar Yukawa theory. It goes from here: $$\langle ...
0
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0answers
14 views

Ratio of oscillation amplitudes of a box on a gasket to floor

So the problem is that I have a box and I put it on a gasket to preserve it from vertical oscillations. The gasket is compressed by the box by a quantity of $h$. The floor is oscillating at frequency ...
0
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2answers
31 views

How to determine the angle of a force?

So when an object is on an incline, I know how to get the magnitudes of the forces but I am having trouble with the direction. Here is an example: So you have calculated the force of friction, ...
1
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0answers
14 views

About atomic transitions

I accomplished my homework but it opened a whole pandora's box of things I do not quite understand, so I would appreciate help. In x direction linearly polarized light excites atom transition from ...
1
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1answer
13 views

Calculating half power frequency (frequency response)

I am having a doubt in calculating half power frequency for a given RLC AC circuit. I have attached images of two questions with their solutions. In the first question, the equation for ...
1
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0answers
26 views

Do these symmetrical looking B field problems have the obvious answer?

I am struggling with two questions whose answers both appear to be trivially zero by symmetry arguments, when I was expecting more derivation to be required. Problem A), An infinitely long wire ...
1
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0answers
25 views

Variational principle perturbation

I am trying to learn 2D SHO and free particle variational principles. However, I came across a perturbation like so: $Ax^2y^2$. The particle is simple harmonic in $x$ and a free particle in $y$? I'm ...
2
votes
2answers
67 views

Is this symmetry factor in Peskin wrong?

I am trying to compute the symmetry factor of a Feynman diagram in $\phi^4$ but i do not get the result Peskin Claims. This is the diagram I am considering ...
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0answers
21 views

Finding current in the circuit 4 [on hold]

When switch is at position 1, current occur in circuit. After a while current increases and time=t, switch is at position 2. What is the current at time t?
2
votes
1answer
26 views

Calculating the potential of 2 spherical perfect conductors with the image method

I am searching for a way to calculate the potential on the surface of two perfect conductors that are spheres. I am not sure my method is correct. Here is a diagram of what I am studying : They ...
1
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1answer
35 views

Quantum Harmonic Oscillators

I'm having trouble with quantum harmonic oscillators and I'm not sure how to approach these questions: . I'd really like to get my head around these concepts but I'm struggling to understand fully. ...
-4
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0answers
24 views

How to calculate speed [on hold]

Please Help I need to calculate the speed of an object, in this case a ice ball with a diameter of 38 mm, propelled vertical through a 38 mm diameter pipe of 300 mm long , and by means of pressurized ...
1
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0answers
28 views

Temperature change in adiabatic free expansion

Consider a gas with fixed number of particles $N$ undergoing adiabatic free expansion from $V_1$ to $V_2$. Apparently we have the following relation $$\Delta ...
-1
votes
1answer
36 views

Drag force on ceiling fan [on hold]

Ceiling fan consumes 80 Watt. if you re track the where all the power go. Then here it is core losses, rotational losses due to bearing, drag force and moment of inertia of ceiling fan. Now how to ...
1
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1answer
28 views

Are there any units involved in the partition function for a classical particle system?

Is the output of a partition function dimensionless or are there units involved? The question as it is: $$E_1\text{=0}K_B\text{,g=1}$$ $$E_2\text{=0}K_B\text{,g=3}$$ $$E_3\text{=0}K_B\text{,g=5}$$ ...
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0answers
53 views

my car is overheating after I just fixed the water pump? [on hold]

Steam coming out the Cool lit jug.. my engine shaking. Also my exhaust pipe throwing Water vapor out. I just changed the water pump..
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1answer
21 views

How does a force get distributed over 6 points? [on hold]

I'm building a truss bridge that needs to support a live load of 16N distributed over a distance of 12.5cm, supported by 6 points, 3 on each truss with equal spacing between them. can anyone help me ...
-5
votes
0answers
15 views

If a motor cyclist was travelling at 12 ms-1, then slows down at 3 ms-2. how long would it take to stop? [on hold]

help me please and make me get to go to my bed because i've school exactly 7 :45 a.m and please don't keep me up waiting for an answer.
0
votes
1answer
37 views

Cart speed and wheel rotation

Say you have a horse drawn cart. Does the outside of the wheel spin at the same velocity that the cart moves forward? The reason I ask is because I am working on a problem where a piece of mud ...
1
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0answers
34 views

How to calculate linear momentum in this elastic collision? [on hold]

A small mass m = 5.0 kg approaches from the left with velocity v and a greater mass M = 40.0 kg approaches from the right with the same velocity. If the collision is elastic and the value of v is v = ...
2
votes
1answer
50 views

Green's function for 1 D hubbard model?

Consider the 1D two-site Hubbard model at half filling $H=-t\sum _{\sigma} (c_{1\sigma} ^{\dagger}c_{2\sigma}+h.c.)+U\sum_i(n_{i\uparrow}-\frac{1}{2})(n_{i\downarrow}-\frac{1}{2})$ where the sum is ...
1
vote
1answer
38 views

What is the gravitational effect inside a electromagnetic shield due to an external electromagnetic field?

I am new in General Relativity. I know that electromagnetic field (or, the electromagnetic energy tensor, $T^{ik}=1/4\pi[1/4F_{mn}F^{mn}g^{ik}-F^i_lF^{lk}]$) can affect gravitation. Now if we take a ...
1
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0answers
11 views

Second-order correction in Quantum-Confined Stark effect

In the wikipedia article, there is a second-order correction in the Quantum-Confined Stark Effect. I could not understand how it was solved. I did not understand the meaning of 2(0) and 1(0) and how I ...
1
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0answers
42 views

How can I compute the average number of collisions of a particle in a spherical container? [on hold]

I have to compute the average number of collisions per unit time of a particle in a spherical container. These collisions are diffuse, i.e., after colliding, the particle bounces off the inner walls ...
2
votes
2answers
42 views

How do you find the projection operator onto an eigenspace if you don't know the eigenvector?

I was working on exercise 2.60 of Nielsen-Chuang which is as follows: Show that $\vec{v}\cdot\vec{\sigma}$ has eigenvalues $\pm 1$, and that the projectors onto the corresponding eigenspaces are ...
1
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1answer
35 views

Normalizing a wave function in a mixed well

So I got this potential and want to solve for the even wavefunctions http://imgur.com/GKAy4nD Since it's symmetric around the origin I need only to look at the interval [0,b] and solve for the ...
1
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0answers
20 views

What is happening kinematically to a car on an icy turn? [on hold]

I am stumped on a conceptual homework question that involves rotational kinematics and friction. Consider a car traveling along a road that encounters a turn covered in an unseen layer of ice. ...
0
votes
0answers
14 views

Mirror question [on hold]

A man stands in front of a plane mirror. The vertical distance between his eyes and the top of his head is 8 cm. Find the minimum height of the mirror so that the man can see all his body.
1
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0answers
4 views

Vertical wall at 3 different temperatures - do the same natural convection coefficient correlations apply?

I have an vertical enclosure that consists of 3 shelves, each with its own temperature and are thermally isolated from each other. We will call the shelves A, B, and C with A being the base shelf. The ...
-1
votes
0answers
10 views

How to calculate the self diffusion of carbon in diamond? [on hold]

What is self diffusion and How to calculate the self diffusion of carbon in graphite and carbon in diamond ?
1
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2answers
29 views

Calculating velocity based on applied force

If I have a block sitting on a spring, ignoring air resistance, with 45N of stored elastic energy in the spring, and the block weighs 500g, what would be the process for calculating its maximum ...
2
votes
0answers
41 views

Two solutions, A+ and A-, for masses connected via springs

My prof gives an example of trying to solve the equations of motion for a series of gliders each connected by springs, with the same spring constant. From looking at the $j-1$ through $j+1$ glider, he ...
-1
votes
0answers
39 views

Beginner level: Is this a correct phase space plot? [on hold]

I am a beginner into chaos and nonlinear dynamics. I was trying to plot the phase space plot for Tent Map using Matlab. The outline of the plot resembles the Tent Map, but I am getting several cross ...
1
vote
1answer
39 views

Graph of energy stored in capacitor?

Question: In an experiment a capacitor is discharged through a constant current. Draw a graph of how the energy stored in the capacitor varies with time. The answer given is: But I seemed to get a ...
1
vote
1answer
40 views

Angular Momentum Expectation Values in Spherical Coordinates

I have a homework problem that asks: Using the spherical harmonics calculate $\langle J_x \rangle$, $\langle J_y \rangle$, $\langle J_z \rangle$ in the state $|l,m\rangle$. Use the derivative ...
-1
votes
0answers
15 views

Calculate angle to hit (x,y) with given, constant air drag [on hold]

Drag constantly decreases velocity by $3\%$ per second. Set $a=0.97$ for simplicity. Original velocity represented by $v$. Horizontal velocity is $f(x)=va^x$ And vertical velocity is ...
0
votes
0answers
18 views

Relative Kinetic Energy on Two Sides of a Spring [on hold]

There is a massless spring on a frictionless surface with two objects, $A$ with mass $m$ and $B$ with mass $M$, attached to the ends of the spring. Both objects are pulled and held at a position where ...
2
votes
2answers
64 views

Transition from 4-potential to E and B [on hold]

In my lecture notes there is a step that i cannot follow: $$\frac{i}{2}[\gamma^{\mu},\gamma^{\nu}] (\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu})=: \sigma^{\mu\nu}F_{\mu\nu}=i\vec{\alpha} ...
2
votes
1answer
85 views

When will the Earth stop rotating?

I looked up leap second in Wikipedia. It is a second added (usually) to clocks to keep them in sync with the atomic clock. It said that 25 leap seconds were added in the last 43 years and that none ...
3
votes
1answer
68 views

Time Evolution of Position Operator

I am trying to understand why $$e^{-it\triangle}xe^{it\triangle}=x-2it\nabla$$ where $x$ is just multiplication operator by $x$. In particular, the text says this can be seen by differentiating with ...