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
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1answer
17 views

Newton's Second law of motion: Elevator problem [on hold]

this is a question about newton's second law of motion that I am a bit stuck on. One end of the cable of an elevator is attached to the elevator car,and the other end of the cable is attached to a ...
-3
votes
0answers
32 views

Path integral method for harmonic oscillator [on hold]

Use the path integral method to calculate the transition $\langle x(f),t(f) \rvert x(i),t(i) \rangle$ for a harmonic oscillator.
0
votes
1answer
39 views

3 pulley and 2 masses,relation between their accelerations

I want to find acceleration of each mass in this system. lets take length of rope between three pulleys as $L$. then we can use this relations ...
0
votes
0answers
45 views

$e^{\mp i \pi \hbar S_z } S_{ \pm} e^{ \pm i \pi \hbar S_z} = -S_{\pm}.$ [on hold]

I am supposed to show that $$e^{\mp i \pi \hbar S_z } S_{ \pm} e^{ \pm i \pi \hbar S_z} = -S_{\pm}.$$ I tried things like the Hadamard equation, but did not really get close to this equation. Does ...
0
votes
1answer
22 views

An unwinding cable problem [on hold]

Suppose a light cable is wrapped around a solid cylinder with mass $M$ and radius $R$. The cylinder rotates with no friction about a stationary horizontal axis. The free end of the cable is attached ...
0
votes
1answer
19 views

How much does the magnetic force change in a solenoid with the distance between turns?

I was looking for answer in my physics book and in Internet but not. I guess that more distance should be an smaller magnetic field but I do not know how much.
0
votes
0answers
19 views

A cantilever problem [on hold]

Consider a cantilever beam AB in equilibrium: End A is fixed and B is free. Force $P$ is applied at free end B. I know that at the fixed end horizontal and vertical reactions act and a reacting ...
0
votes
0answers
20 views

Working with problems including friction forces [on hold]

A body of mass $0.3 kg$ is taken up an inclined plane of length $10$ and height $5 m$ and then allowed to slide down to the bottom again.The coefficient of friction between the body and the plane is ...
-4
votes
0answers
26 views

Velocity and energy of falling object [on hold]

A hammer of mass 1 kg falls freely from a height of 2 m. Calculate the velocity and the kinetic energy of the hammer just before it touches the ground. Does the velocity of the hammer depend on the ...
0
votes
1answer
27 views

How to determine whether an eigenstate of total spin is symmetric or antisymmetric?

Here we have two identical paticles with spin $I$, integer or half-integer, and there are $(2I+1)^2$ states. Each one of them can be uniquely determined by total spin and its orientation, we can use ...
0
votes
1answer
26 views

How to treat partially polarized light with Jones vectors?

I have to calculate the degree of s-polarization (perpendicular) of a transmitted unpolarised light ray when it goes through a glass plate ($n=1.5$) at Brewster's angle (Brewster's window). ...
-1
votes
1answer
16 views

How can we derive the zero work done by the formula of potential energy [on hold]

**We throw a stone through a vertical direction and its fall done so give me explanation about zero work done by potential energy formula. **
0
votes
0answers
17 views

Learning Physics [duplicate]

What's the best way to start learning Physics from home? I haven't touched it since my high school course. I know of Coursera and youtube videos? Are there any other sources that anyone can recommend? ...
2
votes
1answer
45 views

What is the energy of a Gaussian wave packet?

Suppose we have a potential barrier situation, that is $V(x)$ is zero everywhere except on the interval $[-a,a]$, where it is equal to some $V_0 > 0$. Introduce some Gaussian shaped wave packet to ...
2
votes
0answers
48 views

Biot-Savart for current carrying wire

A homework question has made me doubt my understanding of the application of the Biot-Savart law. Question: The magnetic field 43.0 cm away from a long, straight wire carrying current 5.00 A is ...
0
votes
0answers
40 views

Can someone please explain the forces acting on the rod? [on hold]

Can someone please explain the forces acting on the rod.
0
votes
1answer
39 views

Equation of Trajectory [on hold]

I was reading about Lorentz force law and motion of a charged particle under Electric field or magnetic field and I understood how they move in it. But as I was moving further I came across the ...
0
votes
1answer
42 views

Help needed in finding the integral curves given by orbits of one-parameter groups

Equip $\mathbb{R}^2$ with standard symplectic structure and inner product. Consider a Hamiltonian $$H=(x,y)A(x,y)^t$$ where $$A=\begin{pmatrix} \alpha & \beta \\ \beta & \delta \end{pmatrix}$$ ...
3
votes
1answer
41 views

Lagrangian for second-order system

Given an $n$-dimensional second-order system $$\ddot q^i-\sum_{j=1}^n A^i_j\dot q^j=0,$$ where $A$ is a constant matrix, is it possible to find a Lagrangian such that the above equation is the ...
2
votes
1answer
43 views

How to get the linear and angular acceleration generated by a force vector field?

I am working on a physics simulation and I have to calculate the angular acceleration in degrees per seconds squared around the point on the object located relatively to the center of a vector field ...
4
votes
1answer
59 views

Work performed by a stationary object in a gravitational field “on Earth”

I was thinking about this problem: How much work is required to hold an object stationary in a gravitational field? or: How much energy is required to keep an object stationary in a ...
0
votes
2answers
27 views

Potential difference and electric field [on hold]

The potential difference between origin and point P(x,y,z) is given by: $$V-V_0=(30x -15y+xz-4)$$ What is the electric field associated at point P? I am not sure where to start, here. So, ...
2
votes
0answers
41 views

How can I bring water to 90 degrees C? [on hold]

For my coffee I need the water to be 90 degrees Celsuis. Boiling water, however, is 100 degrees. How can I make it 90 degrees? Do I just measure the temperature of the water from my tap, and if it's ...
0
votes
1answer
27 views

Induced potential in a metal

My problem is as follows: A metal whose response is determined by the Thomas-Fermi equation: $(\nabla^{2}-\lambda^{2})V(r)=0 $ , occupies the $z<0 $ infinite half-space: show that the general form ...
0
votes
0answers
33 views

Gravitational force between two rods separated by distance $L$? [on hold]

What is the gravitational force between two rods separated by distance $L$, if they are on the same line each of length $L$ and have mass $M$?.
-1
votes
1answer
47 views

Gauss' Law - Parallel plates [on hold]

A parallel plate capacitor with dielectric (as above), together with its dimensions. Its plates are square. The capacitance is given by the usual formula, $C = \frac{\epsilon _0 \epsilon _r ...
0
votes
0answers
14 views

How many images are formed when theta is decreased between two mirrors? [on hold]

Two mirrors at an angle $\theta$ produce 5 images of a point. The number of images produced when $\theta$ is decreased to $30^0$ is (A) 9 (B) 10 (C) 11 (D) 12 How can I answer this question? ...
0
votes
0answers
45 views

How to find the ratio of the resistance of 2 resistor when they are connected in series and then in parallel? [on hold]

Question: When two resistance R1 and R2 are connected in series, they consume 12W power. When they are connected in parallel, they consume 50 W power. What is the ratio of the powers of R1 and R2 ...
0
votes
0answers
38 views

What is the form of the Hamiltonian for periodic boundary conditions? [on hold]

What would the potential term be for a system with periodic boundary conditions? I know the simple harmonic Hamiltonian, but what about a general system such as a wire? I'm trying to solve the ...
3
votes
2answers
82 views

Can calculations find positive entropy change for heat transfer from cold reservoir to hot body?

I was working on a "simple" heat transfer question and have now confused myself! This question refers to the case where an object is brought into contact with a thermal reservoir, causing the object ...
1
vote
0answers
26 views

Inclined pulley. Finding the $\frac{M_1}{M_2}$ [on hold]

Problem As you can see in the picture, $M_1$ and $M_2$ are attached by a massless rope over a pulley. the height difference of $M_1$ and $M_2$ is $h$. The masses start to move and after $τ$ seconds, ...
-3
votes
0answers
79 views

Which number is bigger, -1 or -2? Discuss your answers by applying examples in Physics [on hold]

Which number is bigger, -1 or -2? Discuss your answers by applying examples in Physics. My answer: -1 is bigger than -2. \begin{align*} \ 3.4 \cdot\ 10 ^{-1} = 0.34 \\ 3.4 \cdot\ 10 ^{-2} = 0.034 ...
0
votes
1answer
22 views

Conditions of friction on constant acceleration [on hold]

If a body is moving with constant acceleration, then what would the frictional force be? Zero In forward direction, In reverse direction all of above
2
votes
1answer
49 views

Predicting balls's movement in well due to fluid flow

I am a total newbie in fluid dynamics. In one of my experiments/open project, my experiment setup is as below: a small ball sits in a circular well (has mass density a bit heavier than water), with ...
3
votes
1answer
34 views

Pion decay: V-A vs. V coupling

For the Decay $$ \pi^+ \to \mu^- \bar{\nu}_\mu $$ the Feynman rules for this tell us that the vertex couples with $\gamma^\mu (1-\gamma^5) / \sqrt{2} $. This gives me the reduced amplitude of $$ M = ...
1
vote
1answer
39 views

Coupled wheel and rod (analytical mechanics)

I am struggling with formulating the equations of motion. Consider a coordinate system with origin in $O$ ($y$ upwards and $x$ to the right), label the center of mass of rod $AB$ with $G$ then: ...
0
votes
1answer
18 views

Angular velocity of disc from induced motion

I came across a question regarding linear momentum $L$ and it's conservation, however I tried and got confused. It reads: A $40kg$ girl stands on the very edge of a rotating disc of mass $50kg$ and ...
0
votes
1answer
37 views

Thrown object with air resistance [on hold]

An object is thrown horizontally from height $h$ with initial velocity of $V_0$. Air resistance is given as $f = -\beta v$ I need to find the velocity and location at any given moment. I understand ...
2
votes
1answer
52 views

From acceleration to displacement

Hi I am a major in Computer science and this question should be really easy for all the physics geniuses here: I have a set of data points from an accelerometer on a moving object that basically ...
0
votes
1answer
54 views

How can electric field representation be obtained from Enge representation using Maxwell's equations?

Suppose we have a long electric capacitor. Let $L$ be its length ($z$ coordinate), $W$ its width ($y$ coordinate), and $D$ its full height (full aperture; $x$ coordinate). Let $L\gg W\gg D$. The ...
2
votes
1answer
60 views

The work-energy theorem

Well here's the question. From some previous excercises we know that from \begin{align} A&=\int F\;ds,\\ &=\int ma\;ds, &&(F=ma)\\ &=\int m \frac{dv}{dt}\;ds, ...
4
votes
1answer
121 views

Chemical and stellar evolution in stars

I'm having an exam soon where I have to discuss/describe the follow figure: It's the first figure I have to explain, and it was on the same slide as the one below, so I'm thinking they are somewhat ...
0
votes
0answers
42 views

Boundary conditions of stream function

I have to do an problem about solving numerically the flow that goes under an airfoil. The airfoil has a flap deployed downwards and I need to solve the mesh that it's under the airfoil. I have drawn ...
-2
votes
0answers
19 views

Waves and sounds [on hold]

A tuning fork whose natural frequency is 440 Hz is placed just above the open end of a tube that contains water.The water is slowly drained from the tube while the tuning fork remains in place and ...
3
votes
2answers
93 views

Hamiltonian for a Lagrangian with coupling

I am dealing with the following Lagrangian density $$\mathscr{L}_{em}= -\frac{1}{2}\rho\omega^2 u^2 +\frac{1}{2}\nabla u:\Sigma :\nabla ...
1
vote
2answers
65 views

How to reconstruct the dependence of the potential from a coordinate?

What is known is that an ion sent along the X-axis of a black box with a speed $V$ returns in a time: $$T=a V^b$$ $a$ and $b$ are some known constants. Having this, can we reproduce the dependence of ...
0
votes
0answers
24 views

Interference of sound: how to calculate the sound intensity at each point?

I need help with the following question: Two speakers are sending out sound in phase with the frequency 2,13 kHz. The sound from the speakers is registered in three points A, B and C. See figure. ...
2
votes
0answers
58 views

Lorentz transformation - Bjorken & Drell

I'm trying to derive (14.25) in Bjorken & Drell (B&D) QFT. This is $$\tag{14.25}U(\epsilon)A^\mu(x)U^{-1}(\epsilon) = A^\mu(x') - \epsilon^{\mu\nu}A_\nu(x') + \frac{\partial ...
2
votes
0answers
51 views

Time functions in general relativity

In my general relativity notes a function $f$ is called time function, if $\nabla f$ is time-like past-pointing. Say that we are in Schwarzschild spacetime and I want to check if $f=t$ is a time ...
-1
votes
1answer
35 views

Projectile at an angle. Finding the angle using conservation of energy [closed]

Ball is thrown at an angle α and at the highest point it's potential and kinetic energy are the same. Find the angle. Use the law of energy conservation. What the professor wanted $mV^2/2 = 2* ...