# Questions tagged [homework-and-exercises]

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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38 views

### How to expand $(D_\mu\Phi)^\dagger(D^\mu\Phi)$ in $SU(2)$

I would like to calculate the following expression: $(D_\mu\Phi)^\dagger(D^\mu\Phi)$ where $D_\mu\Phi = (\partial_\mu-\frac{ig}{2}\tau^aA_\mu^a)\Phi$ and $A_\mu^a$ are the components of a real $SU(2)$ ...
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### Hamiltonian of a system? [closed]

I have a three level lambda system with two ground states $\lvert1\rangle$ and $\lvert3\rangle$ and an excited state $\lvert2\rangle$, interacting with a classical field and the SPP mode of the ...
30 views

### Buoyant force on a stick making an angle theta with the vessel

I was solving this question The answer of the question uses balancing of torques. It uses $L=0.5$m I have problem with the fact that they have used buoyant force $F = \rho V g$. Marking the net ...
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27 views

### Understanding Symmetries and Invariances in Electrostatic Fields [closed]

I'm currently studying electrostatics and I'm having trouble understanding the concepts of symmetries and invariances of electrostatic fields. I understand the basic definitions of symmetry planes and ...
41 views

### Tensor product using Einstein notation [closed]

I have a summation such as $$\displaystyle\frac{1}{2}\sum_{i=1}^{N}\sum_{j=1}^{n}\frac{\partial}{\partial X_{i}}\frac{\partial}{\partial X_{j}}[B_{ij}(\textbf{X})P(\textbf{X},t)]$$ By just applying ...
12 views

### What will be the Maximum Power in the circuit? [closed]

There are two identical batteries each of EMF 2V and internal resistance 1Ω available to produce herat in an external resistance 'R' by passing current through it. What will be the maximum power that ...
31 views

### How do I find the resistance between points M and N? [closed]

This is a network of infinite resistors arranged in the shape of an infinite cuboid extending in the horizontal direction. The resistance of each side of the squares formed is R. We need to calculate ...
74 views

### What does $v$ actually represent in pulley problems?

Let us consider the problem of two pulleys with boxes attached to their ends. One pulley is movable, and the other is not. The problem requires us to find a relationship between velocities of these ...
55 views

### I need an explanation for the time derivative omissions in Landau’s Mechanics: Chapter 1 [closed]

So I have been self-studying Landau and Lifshitz’s Mechanics for a little bit now, and I have been working through the problems, but Problem 3 is giving me some trouble. I solved the Lagrangian ...
69 views

### Question regarding gravitational force as external force

So, I was watching a lecture on YouTube for problems on conservation of energy and momentum and I don't quite understand this: In this question, mass $M$ is released from the peak of the smooth ...
35 views

### Calculating the speed of an ejected electron [closed]

I'm working on some physics exercises and came across this one. Sadly, there is no solution provided, so I was wondering if at least my line of reasoning is correct. ...
63 views

### How is the change in internal energy zero for the following scenario:

in the problem, they are removing partitions one by one. when they remove the first partition they've mentioned in the solution that internal energy will remain constant in the process (and after ...
15 views

### Kinetic energy of a disc rotating about an inclined axis [closed]

What is the kinetic energy of a circular disc of mass M and radius R rotating with angular velocity w about an axis that is inclined to its surface by an angle of 45 degrees? (Please answer using the ...
29 views

### What is the charge distribution on a parallel plate capacitor when one plate is grounded? [closed]

Let's say a large parallel plate capacitor is connected to a DC power supply. Then, the charge on the two plates will be +CV and -CV. If I ground the negative terminal (both the capacitor's and the ...
30 views

### I am trying to derive an expression for the magnetic field of charged particles travelling at significant fractions of speed of light [closed]

I tried using lorentz transformation , which gives me correct answer for speed of light c but when i try to input any other values nearby c it becomes a constant B = 10-7 . q/r² ( (v - u)/ 1- uv/c²)
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### Average force using Heisenberg equation on a bounded particle

My problem states: Prove that the average force that acts on a bounded particle is zero. My question is: How do we represent a bounded particle? I believe that a bounded particle represents a ...
1 vote
53 views

### Orthogonal complement of null vector [closed]

I am trying to solve excercise 8.5 d) from Straumanns book on general relativity (here V is an n-dimensional Minkowski vector space): Prove that the orthogonal complement of a null vector is an $(n-1)$...
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46 views

### Issue with simplifying the equation related to non-uniform acceleration

I am exploring how the cross sectional area of a drogue chute affects its velocity after travelling a set distance. I got this equation: $$m_1 a = m_2 g - \frac12 c_d \rho A v^2,$$ This covers the ...
31 views

### How to calculate the relative speed when three bodies are involved? [closed]

Two trains A and B start from a station and move in parallel tracks with velocities 40 kmph and 60 kmph respectively. A man sitting in train A. watches a lady who walks inside the train B at a speed ...
49 views

### For an objective falling, reaching terminal velocity and then hitting the ground, how can I find the force it exerts on the ground? [closed]

For example object with v=tanh(0.1213)t/0.01236. m=69kg. I thought I had to use F=mv/t but that just gives the net force of the object while falling. I don't know how to find the force impacting on ...
41 views

### Thermodynamics exercise on transformations

An exercise in my book states the following: n = 0.42 moles of an ideal biatomic gas are stored in an adiabatic cylinder with volume $V = 10^{-2} \text{ m}^3$, with an initial pressure equal to one ...
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1 vote
47 views

### Find curve minimizing energy loss due to friction [closed]

I am looking for an ansatz of the following problem: Given a mass $m$ moving in a constant gravitational field along curves $C$ connecting two fixed points I want to find the curve $C_0$ that ...
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### What is this bar for? [closed]

There is a bar in front of the classroom’s blackboard. I wonder what it is for? It shouldn’t be for people to stand on it as then it should be a plank instead of a tube.
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48 views

### How does an object with friction fly off of a disc with angular acceleration? [closed]

Consider the image below An object is resting on a rotating disc with angular velocity w and it is at rest with respect to the disc. Now if we increase the angular velocity of the disc(give it an ...