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

A problem related to the Temperature Coefficient of Resistance [on hold]

I'm having some problem understanding this temperature Coefficient α. I have some questions. I think it doesn't always constant. It just stays constant for a small variation in temperature. Am I ...
-1
votes
1answer
22 views

Help understanding “Pushing blocks against headwind” [on hold]

I am new to StackExchange Physics so I apologize if I do any mistakes. I have been given a problem in dynamics and I have been working on it for a while but I am just getting nonsense. The problem ...
-2
votes
0answers
24 views

A tank of the shape of a right circular cylinder $5$ feet across the top and $9$ feet deep is full of water. [on hold]

A tank of the shape of a right circular cylinder $5$ feet across the top and $9$ feet deep is full of water. How much work is done by pumping the water out of the tank, over the top edge? I need your ...
-1
votes
0answers
43 views

Mechanics; find the equation's path [on hold]

I'm beginning in Mechanics and trying to solve this exercise : We have an orthonormal plan, the coordinates of a moving point M are defined according to time by : $$x(t)=a \sin(\omega t)$$ $$y(t)=b ...
0
votes
1answer
24 views

Steel rod compression under gravity [on hold]

A steel rod with length lying down of 100m (youngs modulus = 200GPa, density 7.85g/cm^3) is stood upwright. How much does it compress by after it is stood upwright. So far I'm just using the formula ...
3
votes
1answer
82 views

What is the force required to move a raindrop?

I'm doing some research on how much force is required to move a typical raindrop (assuming that it is falling straight down) off to the side of X distance. This is for a school project on creating our ...
-1
votes
2answers
47 views

How does gravitational potential energy increase, if field decreases as $h$ increases?

(constants're ommitted) 1-) M=50, m=5, h=5 then Potential Energy = (50*5)/5 = 50 After increasing height 2-) M=50, m=5, h=10 then Potential Energy = (50*5)/10 = 25 Field strength decreases amount ...
-1
votes
0answers
17 views

Compton scattering - going from $θγ^*$ to $θ_{elec}$ [on hold]

I do have the following problem about compton scattering: Find a formula for $$θ_{elec} = f(E_{beam}, \lambda, \theta \gamma^*=90).$$ In other words, how can I go from the rest frame of the photon ...
-2
votes
0answers
20 views

physics - kinematics [on hold]

Two particles one with constant velocity 50m/s and other with uniform acceleration 10m/s2,start moving simultaneously from the same plane in same direction.they will be at a distance of 125m from each ...
0
votes
0answers
39 views

What is the covariant basis around a Schwarzschild black hole?

First of all, I'm not interested in time for this question. So lets consider a 3-manifold whose metric is the spatial part of the Schwarzschild metric, so it has the event horizon and the singularity ...
-1
votes
0answers
17 views

Calculate weight of one object suspended on a wire given angle of depression of wire and weight of another object [on hold]

Suppose I attach two objects to the left and right end of a sturdy wire whose folcrum is in the middle. The wire can't fall off. Using a horizontal line as my guide, I pull out a protractor and ...
-1
votes
0answers
14 views

Commutative Observables Expressed as Functions of a Third Observable [on hold]

For my Quantum assignment, I have to prove that, if two observable operators A and B commute $\exists C $ s.t. A = f(C) and B=g(C) for some real-valued functions f and g. I'd appreciate any amount of ...
1
vote
0answers
24 views

Rod rotated by elastic string [on hold]

A uniform rod $AB$ of length 2m and mass 1kg, has a mass of 1kg attached at $B$. It can rotate freely about a horizontal axis through $A$. The end $B$ is attached by means of a light elastic string ...
-3
votes
0answers
20 views

Using circuit theorems to solve a complex circuit [on hold]

Given a circuit (as shown on the image) , find the change of charge on the capacitor. $E_1 = 12 V, R_1 = 1 k\Omega, R_2 = 30 \Omega, R_3 = 150 \Omega, R_6 = 200 \Omega $ When $\prod$ is closed , ...
-2
votes
0answers
17 views

Finding the overall speed of the car? [on hold]

A car drives $10~\text{km}$ to the east in $15~\text{min}$. Then it turns around and drives $4~\text{km}$ to the west in $15~\text{min}$. What is the overall speed?
0
votes
1answer
56 views

What is the total matter equivalent of the Sun's output per year?

Say we can collect all the energy from the sun's output and all the particles from the solar wind. If we had an energy to mass converter and turned everything into say, carbon, how many kilograms of ...
-2
votes
0answers
16 views

I need help with this question requiring the distance of null electric field [on hold]

The question goes: Two charges q1=-10^-5 C and q2=-9x10^-5 C are placed respectively at two points A and B, 40 cm apart. The electric field is null at point C. Find AC I have tried getting the force ...
-4
votes
0answers
17 views

I need help with this question on electric fields [on hold]

Two charges q1=-10^-5 C and q2=-9x10^-5 C are placed at two points A and B, 40 cm apart. The electric field is null at point C. Find AC
3
votes
0answers
71 views

Calculation of water bulk modulus using equation of state

I simply want to calculate the bulk modulus of water at 50C and increasing pressures. I think I am correctly calculating the new specific volume from the original conditions at (25C and 1atm) to 50C ...
0
votes
0answers
41 views

Plasticine experiment [on hold]

I am doing an experiment in my high school, with plasticine (I did not choose it, it was stupidly given to us). So my idea is to see how the diameter of a plasticine ball (flat bit) varies with the ...
2
votes
2answers
42 views

Basic Relativistic Question - length measurement

A while ago we did an easy, introductory exercise on length measurement. Back then it seemed pretty straightforward but now when I look at it I have trouble understanding the assumption which led to ...
1
vote
0answers
26 views

Exercise about Bethe Ansatz for $N=3$ particles on a ring of length $L$

Suppose there are $3$ bosons living on a 1-dimensional ring of length $L$. The Hamiltonian is given by $$H=-\sum_{i=1}^3\frac{\partial^2}{\partial x_i^2}+\sum_{1\leq j<k\leq ...
0
votes
0answers
30 views

How does the gravitational force exerted on earth? [on hold]

The sun’s mass is about 2.7 x 107 times greater than the moon’s mass. The sun is about 400 times farther from Earth than the moon. How does the gravitational force exerted on Earth by the sun compare ...
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votes
0answers
25 views

How high above Earth's surface would you have to be? [on hold]

Using 6400 km as the radius of Earth, how high above Earth’s surface you would have to be in order to weigh 1/16th of your current weight?
-2
votes
0answers
33 views

Could you please explain whether each of the following is possible for the pilot to measure? [on hold]

An airplane has a gun that fires bullets straight ahead at the speed of 600 miles per hour when tested on the ground while the plane is stationary. The plane takes off and flies east at 600 miles ...
-2
votes
1answer
31 views

Could you please help me find another example of motion under null net force? [on hold]

There are many familiar situations in which the net force on a body is zero and yet the body moves with a constant velocity. Here is one example: A car traveling at constant speed on a ...
-1
votes
0answers
26 views

Propagator massless particle in 1D [on hold]

For a condensed matter application I want to solve the following equation $$ -(\alpha^2 - i \partial_z)G(z,z') = \delta(z-z'). $$ Basically, $G(z,z')$ is the Green's function for a particle with a ...
5
votes
2answers
114 views

Lorentz transformation paradox

I got to solve a simple exercise about special relativity when I kinda came to the conclusion it doesn't stroke with my intuition. The homework-problem The problem was about two people Sam and ...
-1
votes
0answers
17 views

Lorentz force solving and integration [on hold]

I have a question on how to get gyro frequency from lorentz equation. The question is attached below. I have also attached what I have done so far, but looks wrong. How is this question done; a) ...
1
vote
2answers
82 views

Oscillations Near Equilibrium (With Linear Differential Equations)

Case I: The force acting on an object of mass m is $F(x) = F_o(1-e^{\alpha x})$ Case II: The force acting on an object of mass m is $F(x) = F_o(1-e^{-\alpha x})$ where $F_o$ and $\alpha$ are ...
3
votes
3answers
38 views

The storage of kinetic energy in a flywhell?

I am reading a book on physics demonstrations and problems, and one of the problems deals with a flywheel which rotates at maximum angular speed. The density of the flywheel is uniform and the ...
2
votes
1answer
15 views

How do I find the angle with respect to the ground that will cause a projectile launched from the origin to land at the origin? [on hold]

Given an arbitrary non-zero constant horizontal acceleration (like a breeze perhaps), how would one find the angle with respect to the ground (x-axis) that will cause a projectile launched from the ...
3
votes
1answer
57 views

Laser, wire, and a circle of light

So, when I point a laser at a piece of wire (pointed at a specific angle), a circle of light appears on a wall behind it (see image below). I am trying to see why this happens and if there are any ...
0
votes
1answer
33 views

Ladder operators evolution for fermions

For the free Dirac field we have $$ \psi(x) = \sum_s\int d\Omega_{m}\frac{1}{\sqrt{2}k_0}\left(b(\mathbf{k},s)u(\mathbf{k},s)e^{-ik\cdot x}+d^\dagger(\mathbf{k},s)v(\mathbf{k},s)e^{+ik\cdot ...
1
vote
3answers
74 views

A problem related to Work done by falling bodies : Expert's attention much needed! [on hold]

I'm having a lot of trouble with this question, that I've found in my textbook. I've solved it in my own way and it's very simple! But the solution in the book is totally different. It doesn't make ...
4
votes
2answers
101 views

Rectangular window $\psi$ wave-function and the calculus of $\langle p^2\rangle$ for it

I'm currently considering a rectangular window $\psi$ function: $$ \psi(x) = \begin{cases}\left(2a\right)^{-1/2}&\text{for } |x|<a \\ 0&\text{otherwise.} \end{cases} $$ I am interested in ...
1
vote
1answer
43 views

Transformation of the scalar field under Lorentz Boost [on hold]

Assume a Lorentz transformation $\Lambda$ is to be implemented as the unitary operator $U(\Lambda)$ in the Hilbert space of quantum states of the Fock representation upon which the scalar Klein-Gordon ...
0
votes
0answers
29 views

Deceleration of a space shuttle [on hold]

A space shuttle is decelerated by parachutes, which cause a deceleration of $a(v)=-0.04 v^2$. After what time is a space shuttle decelerated to $1m/s$ if it had a velocity of $50m/s$ when the ...
2
votes
1answer
25 views

Activity of a radioactive source - distribution of number of impulses per unit time

I have the following problem: The activity of a radioactive isotope was measured with the result $N=625$ impulses/second. If this measurement were to be repeated, state the interval where we can say ...
2
votes
0answers
12 views

Simplification of matrix-element given the Wigner-Eckardt theorem and Clebsch-Gordon coefficients of a 1,1/2 system

How can I simplify the following matrix-elements $$\left\langle 1,1/2;m_1,m_2\left| S \right| 1,1/2;m_1^{'},m_2^{'} \right\rangle$$ given the Wigner-Eckard theorem $$\left\langle j,m|S|j^{'},m^{'} ...
-2
votes
0answers
15 views

How to express Kirchoff's first law using power flow? [on hold]

How to express Kirchoff's first law using power flow? http://www.regentsprep.org/Regents/physics/phys03/bkirchof1/
2
votes
1answer
56 views

The contraction of fermion field in 1+1-dimensional massless QED

My question comes from the textbook by Peskin & Schroeder, the integral (19.26): $$\begin{align} \int \frac{d^2 k}{(2\pi)^2}\! e^{- i k\cdot (y-z)}\frac{i \not{k}}{k^2} = -\not\partial ...
0
votes
1answer
29 views

Trouble getting the matrix representation of a 4-state Hamiltonian

$\newcommand{\bra}[1]{\left\langle #1 \right|} \newcommand{\ket}[1]{\left| #1 \right\rangle}$I have a simple 4-state Hamiltonian and am trying to find the matrix representation (in order to determine ...
2
votes
1answer
17 views

Scattering Matrix of a Given Circuit - Microwave

This might be an easy question but I couldn't find it in our course book[Microwave Engineering, Pozar, 4th ed] or on internet. I have a homework and one of the questions asks me to find the S-Matrix ...
14
votes
6answers
4k views

Throwing an object around the Earth. Is it possible?

Some of you might be familiar with the cartoon called Astérix. In one of the episodes, Obelix (the really strong fat guy in the stylish striped pants) enters a spear throwing competition. He beats the ...
0
votes
1answer
32 views

How to prove Bloch function is periodic in reciprocal lattice?

How to prove Bloch function is periodic in reciprocal lattice? I saw in some textbooks this formula: $$ \Psi_{\mathbf{k}} (\mathbf{r}) = \sum_{\mathbf{G}} ...
-1
votes
2answers
51 views

Traveling to Mars in 24 Days

I am trying to calculate an electromagnetic rail launch from the Moon but I need to know if humans can survive the launch. Please see the specs below. 150 miles of track Proposed final launch speed ...
0
votes
1answer
20 views

Potential of 2 parallel plates

How can I write down a potential of 2 parallel plates (area $A$) with charge $+Q$, $-Q$ such that V(inf)=0 and V(in) is what I would expect, $Ed = Qd/A\epsilon_0$. Do I have to write a discontinuous ...
0
votes
1answer
39 views

Special Relativity - three body problem

I have a problem with solving three-body problem in special relativity. I know that in general this problem doesn't have good solution, but I have a specific case when it should be good answer. ...
-2
votes
0answers
20 views

Men on the pully palte to lift [on hold]

A plate has a fixed pulley. A men, standing on a plate pulls up with one end of the rope to try to lift the plate and himself; the other end of the rope is over the pulley to fixed on the ceiling, ...