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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1answer
23 views

An impossible relationship between variables

This book chapter defines $CV$ as follows: $$ CV^2 = 2\pi\nu^2\int^\frac{V_{th}-V_{ss}}{\sigma_V}_\frac{V_{r}-V_{ss}}{\sigma_V}dxe^{x^2}\int^x_{-\inf}dye^{y^2}(1 + erf(y)) $$ However, Figure 15.2 in ...
0
votes
1answer
28 views

Solving for the firing rate of a model neuron

I'm trying to decipher Figure 15.2A on page 442 of this book chapter. It plots the firing rate $\nu$ of a model neuron against its mean current $\mu_c$. The equation used to calculate the firing ...
-4
votes
0answers
29 views

Infinite potential well question? [on hold]

A particle with mass m is in an infinite potential well in $|x|\leq \frac{a}{2}$. 1) find the two lowest levels of energy and their eigenstates . In $t=0$,the particle is ...
0
votes
0answers
41 views

10 Harmonic Oscillators - Probability of finding one in state n=0

Given are 10 harmonic oscillators with a total energy of $E=2h\nu$. Note that the ground states are not included, since the calculations do not need them! e.g. $E_n= \hbar \omega (1/2 + n)\approx ...
-3
votes
0answers
33 views

Finding the speed of a car

There is one car which got stolen which goes from the point $30$ in the negative sense of the "$x$" axe towards the point $0$ and has a constant speed of $160\text{ km/h}$. Another person notices ...
1
vote
0answers
12 views

Finding Far field Fraunhoffer diffraction for infinite sinusoidal phase grating

Question b) What confuses me is that given the transmission function, do you need to get it into a form which is similar to $\exp(iK\cos x)$? Is there not a convolution with another function as it ...
-5
votes
0answers
21 views

effect of earth's magnetic field on period of pendulum [duplicate]

I want to know will earth's magnetic field change period of pendulum if pendulum is made up of- 1. ferromagnetic material 2. paramagnetic material.
4
votes
3answers
413 views

How far up an object is its gravitational potential energy taken from?

This is quite a brief question but, Is the $h$ value in $mgh$ taken from an object's base, middle of top. For example, if a person was $1.5m$ in height and they were standing on a hill of height ...
0
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0answers
31 views

Altering a model to account for another variable

A question in my textbook asked me to find a general equation for depth fallen by an object of mass $75kg$ thrown from a bridge whilst tied to an elastic rope. Below the bridge there is a stream of ...
-2
votes
0answers
14 views

How to find forces in wires at equilibrium [on hold]

I need to find tensions in suspensions wires on the picture: I wrote 4 equilibrium equations for moments in A, B, C, D and equilibrium about y-axis, but i got matrix with rank two. ...
-1
votes
1answer
17 views

Eletric field on a semi circular ring, different charges on each quarter of a ring

In this image to calculate the net eletric field is used integration from 60 degrees to -60 degrees. Ok for me by now. But then I was doing this question, number 26: And he solves by doing that: ...
0
votes
2answers
34 views

A car honking it's horn, how long until the car hears the sound reflected? [on hold]

A car is traveling with a constant speed v on a straight road which forms an angle α with nearby straight wall. When the car is at a distance l from the wall the driver presses the horn briefly. What ...
0
votes
2answers
46 views

Problem with tracing over the environment and obtaining reduced density operator

I'm reading an article by Bas Henson given here. On page 25 he deals with the double slit experiment Given the wavefunction which is his equation 1.75, he claims he has traced over the environment ...
-4
votes
2answers
44 views

How to determine the angular velocity of a particle with mass $m$ and charge $q$ in a constant B field?

$\textbf{PROBLEM:}$ A particle with mass $m$ and charge $q$ moves in a constant magnetic field $B$. Show that, if the initial velocity is perpendicular to $B$, the path is circular and the angular ...
0
votes
1answer
35 views

Help with proving a relation

I am trying to see if the following relation, \begin{equation} \frac 12 g_{ij}\frac{d^2\eta}{du^2}+\frac 12 g_{ij}\frac{d\eta }{du}+\frac 12 \frac{\partial g_{ij}}{\partial x^j}\frac ...
-3
votes
0answers
19 views

Magnitude of force of air resistance [on hold]

A 68 lbf prefabricated slab is hoisted by a rope. The rope pulls with a force of 751.9 N at an angle of 6.6° to the left of vertically upward. The only other force acting on the slab is the force of ...
-1
votes
2answers
36 views

Block over a Block Problem.

This a block placed on block problem. In this problem, A block with mass 40 kg in placed on a block of 60kg which lies on a frictionless surface. The coefficient of friction between 40kg mass and 60kg ...
-1
votes
3answers
48 views

How to calculate the linear speed without angular velocity? [on hold]

How would you calculate question (f) the linear velocity, without a angular velocity. The radius of the circle is 0.6m. The answer (linear velocity) should = 1.84 m/s
-3
votes
0answers
27 views

Radio active isotopes [on hold]

Radio active 54fe at mass 15g is given activity of 3700000 meters per second and then inserted into an engine.After 100days of continuous use,the crank case oil was found to have a total of activity ...
-5
votes
0answers
27 views

How to form a density matrix? [on hold]

forming a density matrix when two independent states are there
-2
votes
1answer
26 views

Problem: When does a constant velocity catch up to a certain acceleration? What is the maximum acceleration? [on hold]

Physics noob here. Romeo is at x = 0 at t = 0 when he sees Juliet at x = 6m. (a) He begins to run towards her at v = 5m/s. She in turn begins to accelerate towards him at a = −2m/s2 . When ...
-1
votes
1answer
29 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: ...
-6
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0answers
55 views

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

How to solve this question regarding quantum mechanical wavefunction ?
2
votes
1answer
50 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
71 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
1answer
36 views

One stupid question about Dirac mass term and Grassmann numbers

Let's have Dirac mass term in lagrangian: $$ L_{M} = \bar{\Psi}\Psi $$ Lagrangian must be real-valued, i.e., its Hermitian conjugation doesn't change it. But due to Grassmann nature of spinor fields, ...
2
votes
1answer
49 views

Show that the boundary layers diffuse out from the plate with speed $\sqrt{\frac{\nu}{t}}$

I was wondering if somebody would be able to help me with this problem. I know how to solve it using dimension arguments but I'm unsure what is meant by transformation techniques. Any help would be ...
0
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0answers
12 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
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0answers
29 views
+50

Is capacitance calculated over a finite volume or over all space?

Is the capacitance of a system of conductors calculated in a finite volume or over all space? My question is motivated by the following problem. A volume $V$ in vacuum is bounded by a surface $S$ ...
0
votes
1answer
23 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
16 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
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1answer
30 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
94 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
31 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
44 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
38 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
14 views

Transition from the second excited state to the ground state in 3d oscillator [on hold]

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 ...
0
votes
4answers
98 views

Does a flying bullet get KE from gravity?

A projectile P is shot horizontally at 9.8 m/s from a height of 4.9 m, considering no air friction, after a second it will have v = 9.8 m/s on the x-axis and v = -9.8 on the y-axis. Because of ...
1
vote
1answer
78 views

Rolling down an arbitrary hill with friction

I had in mind this physical situation of a point mass rolling down a hill of some arbitrary shape ($y=y(x)$, for instance a parabola about $x=0$), with a peculiar friction force whose "expended work" ...
-6
votes
0answers
16 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 ...
-4
votes
0answers
18 views

Kinematics Question: Velocity and Acceleration Polygons [on hold]

I think I've been doing too many of these without much rest because I am stumped. The Curved slider mechanism is what is confusing me: Dimensions of a simple 2-bar linkage are given in the attached ...
-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
104 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
32 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. ...