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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-1
votes
1answer
22 views

How can I estimate CO2 emissions for a vehicle travel distance

How can I properly estimate CO2 emissions for a given travel distance (of a private vehicle)? I found the following formula, but I'm not sure that it's correct: ...
-5
votes
0answers
39 views

how to solve the following question about quantum mechanical wave function? [on hold]

How to solve this question regarding quantum mechanical wavefunction ?
1
vote
3answers
50 views

Why does a sheet of paper fall slower than the same when rolled into a ball?

It depends on volume but both the sheet and the sphere have the same volume.Does surface area play any role here?
2
votes
1answer
36 views

Derivation of geodesic deviation equation from two neighbouring geodesics

I'm stuck trying to follow Foster and Nightingale's derivation of the geodesic equation from two neighbouring geodesics $x^{a}\left(u\right)$ and $\tilde{x}^{a}\left(u\right)$ joined by a ...
2
votes
0answers
40 views

Poisson brackets and magnetic field [on hold]

I'm a maths student trying to teach myself some physics so sorry if I'm missing something simple here. I think the main problem is lack of experience with the Levi-Cevita symbol. We have a particle ...
-1
votes
1answer
18 views

Statics Vector Question [on hold]

I need help with this problem image of problem: http://postimg.org/image/87o0tyfyp/ I could answer the question if I had a second angle but I don't even know where to begin to solve the question. ...
0
votes
0answers
10 views

Question related to charged concentric conducting shells

There is a charged conducting spherical shell given a certain positive charge.Another larger spherical shell is given the same negative charge.The first shell is now placed inside the second shell so ...
0
votes
0answers
16 views

Field outside of conducting surface held at potential

Problem 1.17 in Jackson (3rd ed). A volume $V$ in vacuum is bounded by a surface $S$ consisting of several separate conducting surfaces $S_i$. One conductor is held at unit potential and all the ...
0
votes
1answer
22 views

Help with this question (Eletric Fields, Dipole) [on hold]

The answer in the textbook in the solutions manual is the following: I didn't undestand the last step. He said he did a binomial expansion, I just can't figure out! Appreciate any help.
0
votes
0answers
14 views

If we considered chiral perturbation theory with coplex $\phi$-s, wold the next lo leading order renormalization $\gamma$-s change?

The Lagrangian of chiral perturbation theory (with two quark flavors) is written using the following matrix $U$ $$U=e^{i\sigma^i\phi_i/f}$$ where $\sigma^i$ are the Pauli matrices, $\phi_i$ are three ...
0
votes
1answer
28 views

Difference in resistance between two configurations

Given a spherical shell of a conducting material with radius $a$, surrounded by a poorly conducting material between it and another conducting shell with radius $b$, you can calculate the resistance ...
-1
votes
0answers
38 views

It is possible to have a situiation in which $|\mathrm{d}v/\mathrm{d}t|$ is not zero but $\mathrm{d}|v|/\mathrm{d}t$ is? [on hold]

Please explain the following in detail: It is possible to have a situation in which $\displaystyle\biggl\lvert\frac{\mathrm{d}\vec{v}}{\mathrm{d}t}\biggr\rvert\neq 0$ but ...
6
votes
2answers
91 views

Infinite square well that suddenly decreases in size

A well known exercise in basic quantum mechanics is the sudden (diabatic) increase of the length of an infinite square well. Now consider a particle in an eigenstate of an infinite well that is ...
2
votes
1answer
27 views

Wave equations - how to get a real solution from imaginary roots

Im trying to follow the derivation on how to solve Laplace equation used in my fluid dynamics course. We are trying to solve for the velocity potential in potential theory. So far we have this: ...
0
votes
0answers
19 views

Show that the minimum energy value for a given $l$ increases as $l$ increases

"Consider a particle in a central field and assume that the system has a discrete spectrum. Each orbital quantum number $l$ has a minimum energy value. Show that this minimum value increases as $l$ ...
2
votes
1answer
31 views

Derivation of relativistic mean free path

I am working through a short derivation found in Abramowicz 1991 regarding the mean free path of a photon. We have a fluid moving in a particular direction with velocity $v$ and in an inertial rest ...
1
vote
0answers
35 views

How to make two equations dimensionless? [on hold]

I recently got set this problem and am having trouble scaling the resulting equations. Any help would be appreciated. An incompressible thermal conducting fluid is contained between two infinite ...
0
votes
0answers
11 views

Find elongations of truss members [on hold]

Members AB and BC are made of steel (E=29*10^6 psi) with cross-sectional areas of 0.80 in^2 and 0.64 in^2, respectively. For the loading shown, determine the elongation of (a) member AB, (b) member ...
0
votes
1answer
37 views

Relationship between Toffoli gate and Deutsch gate

I am reading a book called "Quantum Computing for computer scientists" and stuck at this exercise for a day. Bellow is the description of Deutsch gate: And here is the description of Toffoli ...
0
votes
0answers
13 views

Transition from the second excited state to the ground state in 3d oscillator

The problem: 3d harmonic oscillator is in a second excited state. Suddenly a perturbation is applied which depends only on the length of the position vector $|\vec{r}|$. Can the oscillator fall into ...
-6
votes
0answers
15 views

What axial forces does the vertical load induce? [on hold]

What axial forces does the vertical load P induce in the members of the system down in the figure? Neglect there weights of the members themselves and assume an ideal hinge at A and a perfectly ...
-3
votes
0answers
14 views

Kinematics-Motion in 1 dimension [on hold]

A motor car moving at 20m/s can not come to a stop in less than 3s while for a truck this time interval is 5s. On a highway the car is behind the truck both moving at 20m/s. The truck gives a signal ...
1
vote
2answers
91 views

The Twin Paradox using reference frame following the ship

The Twin Paradox is undoubtedly one of the most discussed things in special relativity and have a tendency to confuse most of us. Classically, it's resolved by either stick to one of the three ...
-4
votes
0answers
30 views

Relativistic velocity in Special Theory of Relativity [on hold]

Prove that, 0.5 m*v^2 , where m = M / (1- (v^2 / c^2))^0.5 ["M" is original mass, and "m" is mass with velocity] doesn't equal to the the Kinetic Energy of a particle moving at relativistic velocity. ...
-2
votes
0answers
13 views

Kinematics-Motion in one Dimension [on hold]

A man is standing on top of a building 100m high. He throws 2 balls vertically, one at t=0 and the other after a time interval(less than 2s). The later ball is thrown at a velocity of half the first. ...
-1
votes
0answers
22 views

Frictional pulley [on hold]

Whenever we do any pulley problems, generally, it is mentioned, that the pulley is $massless$ and $frictionless$. But, what will happen if it is given that the pulley is frictional. I had gone a ...
0
votes
0answers
34 views

Charge distribution on uncharged conducting sphere

I am trying to solve the following problem: A charge $q$ is brought to a distance $d$ from the center of an uncharged, conducting sphere of radius R. What is the charge per unit area of the sphere ...
0
votes
1answer
38 views

(homework) finding location of third point charge [on hold]

having trouble with the following There are three point charges along the x-axis: q1 is +3µC, located at the origin q2 is -5µC, located at x = +0.200m q3 is -8µC Where is q3 located if the net ...
0
votes
0answers
43 views

Object pursuing exactly toward an uniformly moving object, with a twist

A friend of mine asked me about a problem he faced in an exam, but I happen to be rusty on this and can't seem to even understand it's implications, nevermind solve it. At $t=0$ an object A in ...
1
vote
1answer
39 views

Finding the approximate distance between molecules in a gas

I have a problem to understand why the below derivation can be used to find the distance between molecules: This example is an approximation. We are supposed to find the average distance between the ...
-1
votes
0answers
25 views

How to measure the diameter of a Glass tube? [on hold]

I'm working on something and I need to find the diameter of a glass tube. I wanted to use diffraction pattern to find the diameter of my tube. but the problem is that my tube is transparent. Anybody ...
-6
votes
0answers
50 views

Theoretical physics [on hold]

Hi every one I am student who has a high interest in the Ising model. Please I have a question and I hope someone can help me
1
vote
2answers
57 views

Projectile motion of Golf ball- Can projection height be calculated just from initial velocity and travel time? [on hold]

A Golf ball projected with a horizontal velocity of 30 meter per second and takes 4 second to reach the ground. Calculate the height the golf ball was projected from. Calculate the magnitude of ...
0
votes
1answer
39 views

water fountain with a pipette

if you get some hot water in a pipette an put the pick of it on the top the water will jump out f pipette and make a fountain.I wondered if any one could tell me what is the reason?
-1
votes
2answers
61 views

Very basic question about vector

The vectors $a = (2,-1,-2)$ and $b = (0,-3,4)$ are given. Determine $a$:s parallel and normal vector to $b$. Obviously the parallel vector should be the dot product $a \cdot b$ times the unit vector ...
-5
votes
0answers
32 views

p=aV+b, finding Q and L [on hold]

I must find L and Q from p=aV+b. I calculated the L like: ...
2
votes
3answers
81 views

Does acceleration follow the same addition like velocity?

Two frames have relative velocity $u$, but an object in one is initially at rest and in the other has velocity $v$. If it then starts to accelerate, the acceleration measured in both frames is equal. ...
0
votes
1answer
33 views

Gravitational intensity [closed]

I calculated the gravitational intensity and potential at a point P due to a horizontal linear mass distribution of length '$L$', mass '$M$' and uniform linear density at a distance '$R$' apart from ...
-1
votes
0answers
22 views

PMOS Gate Oxide Capacitance Equation?

I'm having a hard time finding the correct equation for the question shown below. Any ideas on which one I'd need? I've seen this equation: I understand that $\varepsilon_{ox} = \varepsilon_r ...
0
votes
1answer
35 views

Doped PNP Bipolar Transistor

When doping a PNP bipolar transistor, does it matter which parts are doped by what amount? The picture below will show my question. Am I right in saying that the Emitter is connected to one P region, ...
0
votes
0answers
31 views

Transform coordinates to an other coordinate system and back using the Lorentz Transformation [on hold]

So in order for special relativity to be self-consistent one should be able to transform some event coordinate to an other reference frame and then transform it back yielding the same as we started ...
-1
votes
0answers
20 views

technique to know the output of diffraction [closed]

How to know the output pattern of diffraction if I know the function of the grating and function of incoming light source?
-2
votes
0answers
54 views

Unitary transformation problem [on hold]

In some of the books of quantum optics, it has been said unitary transformation change the basis along with preserving the inner product. that means, $H'=U^+HU$ where $U=\exp ix_mH/\hbar$ Here, ...
0
votes
0answers
15 views

Waves ionsphere?

Explain why the ionosphere can be treated as a plane mirror when transmitting short-wave radio, even though it is a curved surface. Is it because the area involved is small?
0
votes
1answer
40 views

Barycenter and relative coordinates for schroedinger equation of the hydrogen atom

Heyho, i just realized i am not sure how one gets from: $\Big(-\frac{\hbar^2}{2m_e} \Delta_{r_e} - \frac{\hbar^2}{2M_P} \Delta_{r_p} +V(r) \Big)\Psi(r_e,r_p) = E \Psi(r_e,r_p)$ to: ...
-2
votes
2answers
28 views

Thunder cloud problems

In the problem "On a cloudy day,a man hear a thunderclap 5s after seeing a lightning flash.How far away is the man from the source of thunder." Explainer said that the difference of the time taken to ...
2
votes
2answers
67 views

Showing that the magnetic field inside an infinite current carrying cylinder is zero

I'm doing some self studying of introductory physics, and was working a question from a textbook that has several parts. The first few parts asked me to show that the magnetic field of an infinite ...
0
votes
2answers
52 views

Ball throwing problem [closed]

A ball of mass 0.2 kg is thrown vertically upwards by applying a constant force by hand.if the hand moves 0.2 m while applying the force and the ball goes upto 2 m height further, find the magnitude ...
1
vote
0answers
97 views

Quantum Liouville-Propagator Operator Trace Identity [on hold]

How can i proove: $Tr(Ae^{Lt}B)=Tr(Be^{-Lt}A)$ were $A$ and $B$ are Observables in the Schrödinger picture and $L$ is the Quantum Liouville super-operator defined by: $LA={ i \over \hbar} [H,A]$ ...
0
votes
0answers
22 views

Calculation of lowest energy [closed]

5 spin 1/2 particles are under an 1D harmonic oscillator potential.What is the lowest energy states of the system? I primarily tried it considering no degeneracy of any eigenstates.But I got it wrong. ...