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.

Filter by
Sorted by
Tagged with
0
votes
1answer
39 views

Normal force in this example? [on hold]

My question here is, why there is no Normal Force, because object A is on the ground. Is it because the normal force only exist when we move object along some path?
0
votes
0answers
87 views

Angle between velocity and acceleration vector, and interpretation of pathway [closed]

I just started studying mechanics, and I am stuck with the following question: $$\vec{r}(t)=a \sin(\alpha t^2)\hat{x}+b \cos(\alpha t^2)\hat{y}$$ I was asked to find the formula that expresses the ...
1
vote
1answer
64 views

Time for a particle to reach the centre of a potential on a straight path [closed]

I'm working on a problem in classical mechanics. We have a particle moving in a potential $V=\frac{-a}{r^n}$ where $a$ and $n$ are given constants. Now we let go of the particle at the position $r(t=...
2
votes
1answer
64 views

Finding the quadrature variance of a superposition of squeezed coherent states

How do you find the quadrature variance of a state $$\lvert x\rangle =\lvert a,b\rangle +\lvert a,-b\rangle$$ where $\lvert a,b\rangle = D(a) S(b) \lvert 0\rangle$? $\lvert x\rangle$ is a ...
0
votes
1answer
69 views

What are the equations of motion for a pendulum in $n$ dimensions?

Consider a pendulum formed of a light rod of length $l$ and a point mass $m$. At the pivot the pendulum experiences friction with coefficient $b$, and an agent can exert torque $\tau$. In 2 ...
-1
votes
0answers
17 views

(NLM) Find Acceleration of Both Blocks so that they won't lose their contact [on hold]

'a' and 'x' have numerical values. All pulleys are attached to some mass. Direction Of Acceleration is Right(+x axis)
0
votes
0answers
38 views

Two dielectrics and one charge (image problem) [closed]

There are two regions: A dielectric with permittivity $ \epsilon_2$ in the region $ z>0$ A dielectric with permittivity $\epsilon_1$ in the region $ z<0$ And a charge $q$ is situated at $(0,...
1
vote
0answers
30 views

How much energy does it require to fuse a proton with a nucleus? [closed]

If calcium 45 is bombarded with protons and one proton is to be added to the nucleus of the atom, how much energy is required to overcome the electromagnetic force?
0
votes
0answers
31 views

Wich is the correct flow rate $Q$ solved with iterations?

I have a little question about this problem I computed the right answer this way First I applied Bernoulli between the top and the exit $$\frac{P_{t}}{\rho g}+z_{t}+\frac{v_{t}^2}{2g}-H_{1}-H_2-H_{\...
0
votes
1answer
33 views

Tangential Motion of an Object Attached by a Radial Elastic String [closed]

A toy car travels in a horizontal circle of radius 2a, kept on track by a radial elastic string of unstretched length a. The period of rotation is T. When the car is speeded up the string stretches ...
1
vote
1answer
32 views

Does this wave function from Zettili book (Quantum Mechanics) violate uncertainy principle?

I am not sure whether my question counts as homework and exercises or not, because I already know the answer. The problem is, I find Zettili answer rather unsatisfactory. Problem 1.11 (a) Find the ...
1
vote
1answer
191 views

Dielectric above and below the xy plane

This is problem 4.25 from Griffiths' electrodynamics, it says: Suppose the region above the $xy$ plane is filled with linear dielectric of susceptibility $\chi_e{}'$ , and the region below the $xy$ ...
-6
votes
0answers
26 views

New problem in classical mechanics [duplicate]

the question is,Two small weights P and Q connected by a flexible but I extensible cord of length l are hung over a perfectly smooth circular cylinder of radius r if l=r and P=2Q find the position ...
2
votes
1answer
49 views

What is the gravity on a “partial” ringworld?

This was inspired by https://worldbuilding.stackexchange.com/questions/149706/life-on-the-broken-ring-an-issue-of-size. Let's say I have a part of a Ringworld (see link for specifications). ...
0
votes
0answers
8 views

Magnetic susceptibility for particle on a ring

I consider particle on a ring in magnetic field. The presence of magnetic field shifts the particle momentum and I understand to find magnetic flux through the ring. Then, how can I find the ...
0
votes
1answer
78 views

Different formula to find $2\times 2$ Hamiltonian's eigenvalues [closed]

Consider the Hamiltonian $$ \left[ \begin{matrix} E_1 & -A\\ -A& E_2\\ \end{matrix} \right] $$ where $A$, $E_1,E_2$ are real numbers. I have seen a different formula to ...
0
votes
1answer
31 views

What is the unit of the current in a square barrier model?

In Quantum Mechanics textbooks, the equation for a electron tunneling through a barrier is $$-\frac{\hbar ^{2}}{2m}\frac{d^{2}}{dx^{2}}\psi \left( x\right) +U\psi \left(x\right) =E\psi \left( x\right)...
0
votes
3answers
31 views

Constant Pressure Cylinder

The solution to this states that "pressure of the gas is constant." What implies this? Is it because the piston was elevated then stopped? If the gas pushed the Piston all the way up to where it ...
0
votes
1answer
30 views

Calculating entropy change in this irreversible process

A 15.0-kg block of ice at 0.0°C melts to liquid water at 0.0°C inside a large room at 20.0°C. Treat the ice and the room as an isolated system, and assume that the room is large enough for its ...
2
votes
1answer
65 views

Electrons expelled from the wave [closed]

The intensity of the electric field of an electromagnetic wave varies according to the law:$$E\left(t\right)=E_{0}\left(1+\cos\varOmega t\right)\cdotp \cos\omega t,\varOmega=2\cdotp10^{15}s^{-1},\...
4
votes
1answer
79 views

Why the geomagnetic field become stronger when solar wind is stronger?

The following description is from the webpage of Niels Bohr Institue's Former Centre for Ice and Climate The Earth reacts to the solar wind by increasing the strength of the shielding magnetic ...
-1
votes
0answers
127 views

What would theoretically lead to a greater burn if both materials are kept at a constant temperature when applied to the skin? Water or Brass? [closed]

This is a question that would help with the understanding of specific heat and conductivity and which has a greater effect when it comes to transfer of energy between objects.
2
votes
0answers
61 views

Band Structure for free electrons

Consider a BCC lattice. How can I explicitly calculate the expression of the n$^{th}$-energy band $E_n(k)$ with $n=1,2,3,4$ for free electrons from $\Gamma$ to $N=\frac{2\pi}{a}(1/2, 1/2, 0)$ as a ...
1
vote
1answer
38 views

2 dimensional massless scalar field propagator in position space

I have been trying to calculate the massless scalar field propagator in position space by directly Fourier transforming the momentum space propagator. $$\int{d^2p\frac{1}{(p^0)^2-(p^1)^2}e^{-i(p^0t-p^...
0
votes
1answer
20 views

Motion of particle in uniform magnetic field with friction propositional to velocity [closed]

A positively charged particlewith charge "q" is at $ (0,0,0)$.There is a uniform magnetic field $ \vec B= -B \hat k$. The particle is given velocity $\vec u= u \hat i$. A resistive friction acts on ...
0
votes
1answer
34 views

How work interferes into law of conservation of energy problem?

A 10kg block slides down a hill that is 200m tall as shown in the figure below with an initial speed of 12m/sec. a) What is the speed of the block when it reaches the bottom of the hill at position ...
1
vote
0answers
41 views

Constrained Motion [closed]

There are two bodies viz. A and B which are placed on a horizontal surface. The free end P is being pulled by a constant force of 1 N. Find the acceleration of free end P? My approach Sign ...
0
votes
1answer
33 views

Effect on mass of change of angle on hinged beam

I am trying to calculate the change in weight (if any) on point B of a beam hinged at point A if the angle changes. e.g. A bridge hinged on solid ground (Point A) reaching onto a floating pontoon (...
0
votes
0answers
22 views

Quantizing Complex Klein gordon Field, how do they get rid of Crossed terms?

I was working through the exercises on Peskin and Schroeder specifically 2.2, I get the Following equation: $ Q=\frac{1}{2}\int \frac{d^{3}p}{(2\pi)^{3}}(a_{p}^{\dagger}a_{p}-b_{p}^{\dagger}b_{p}+a_{p}...
2
votes
1answer
73 views

Contradictions in electric field of infinite uniform charge distribution [duplicate]

This question stems from the exercise 2.50 of Griffith's Introduction to Electrodynamics, which I am rereading. In the problem, he asks to find the charge density of a volume when the electric field ...
0
votes
1answer
64 views

How much faster does time pass in a star orbiting a black hole compared to earth?

I want to calculate the shifting of the time in a star that orbits a supermassive black hole, i already know that if the star is orbiting at 5000 km/s with respect to earth the time will be 1/(1-(5000^...
0
votes
2answers
47 views

Confusion regarding Ricci Scalar

Source: Thomas Moore's A General Relativity Workbook Equation 1: $R= g^{\mu\nu}R_{\mu\nu} = R^\nu{}_\nu$ Equation 2: $R^{\mu\nu}=g^{\mu\beta}g^{\nu\sigma}R_\beta\sigma$ Question: Does $R$ also ...
1
vote
2answers
33 views

Rolling motion in a inclined plane [closed]

what happens to a rolling ball when it enters to a frictionless surface? does the ball keep rolling forward? how to explain the motion of the ball in the BC and CD surfaces?
0
votes
0answers
38 views

Geodesic equation for spherical symmetric gravitational field

Let $h_{\mu\nu}= g_{\mu\nu}-\eta_{\mu\nu}$ be of the form: $$\begin{pmatrix} -2\phi(r) & 0&0&0 \\ 0& -2\psi(r)&0&0\\ 0& 0&-2\psi(r)&0\\ 0& 0&0&-2\psi(...
1
vote
0answers
40 views

Linear momentum of a rotating system

So say we have a thin rod resting horizontally on a flat frictionless surface. The rod is pinned at its center, and a small mass collides perfectly inelastically with one end of the rod after moving ...
2
votes
2answers
78 views

How to calculate gravity inside of a circle of mass?

I've been reading about the Shell Theorem and how the gravitational force inside of a sphere is equal to zero. I was wondering if the same was true for a circle, but couldn't find any definitive ...
0
votes
0answers
31 views

Boundary term in the holographic circular Wilson loop

Our professor has given us the holographic circular wilson loop as homework. He gave us the following reference https://arxiv.org/abs/hep-th/9904191 https://arxiv.org/abs/hep-th/0501109 and told us ...
0
votes
1answer
34 views

Factor of $1/2$ in $TT$-OPE [on hold]

I'm trying to calculate the TT OPE in a bosonic theory. I'm missing a factor of 1/2 in the least-singular term. We have (following Di Francesco) $$\langle \partial \phi(z) \partial \phi(0) \rangle = \...
0
votes
1answer
25 views

Electric dipole torque problem [closed]

Problem 4.6 from Griffith's book: To solve it, we construct an image dipole $ \vec p_i$ with opposite polarity then find the torque $ \vec N = \vec p \times \vec E $ I'm having trouble knowing how ...
0
votes
2answers
77 views

Colored fringes in Young's Double Slit Experiment (YDSE) using white light

Suppose we use a monochromatic light in YDSE. We observe the regular type of fringes of mainly the same color and they fade away as the distance from central maxima increases. But with white light we ...
2
votes
1answer
46 views

Conservation of energy with friction on a pool ball

I have a problem where I am given the mass $m$, radius $r$ and friction $\mu$ between a pool ball and table. The ball is not initially moving but at $t=0$ is struck by an impulse $$p=\int_{-\epsilon}^...
0
votes
0answers
57 views

Gluon-gluon scattering: Problem 8.28 in Griffiths' “Intro. to Elementary Particles” (2nd edition)

The "Introduction to Elementary Particles Instructor's Solution Manual" (available online) does not give the solution to this particular problem, which asks: (a) Draw the lowest order diagrams (there ...
-2
votes
0answers
24 views

How is the gyrating motion of a charged particle in a non uniform magnetic field?

In a uniform magnetic field it is simply a circle in 2D(x,y) and a helix with constant pitch in 3D(x,y,t). How does this change when the magnetic field is not uniform ? For reference : $\mathbf B = ...
0
votes
2answers
113 views

Simplified calculation of the amount of fuel required for a trip — are my calculations faulty?

I've been always fascinated with how easily scifi characters travel around the Solar system and sometimes the galaxy. They just hop into a spacecar and go wherever they want. So I've come up with a ...
0
votes
3answers
62 views

$pV$ work and Specific volume

I am working on a $pV$ work exercise. I am given $P_1$, $P_2$, and $V_1$; we can solve for $V_2$. I am also given mass. I am told that the $pV$ relationship is $pv^{1.2}=const.$, where $v$ is ...
1
vote
0answers
14 views

Direction of electric field due to a quarter ring at a point on its axis [closed]

I stumbled upon a question in my exam wherein I had a quarter ring in y-z plane of radius R and charge density lambda. I had to calculate the electric field at a point on X axis at a distance R from ...
0
votes
1answer
96 views

Two energy level classical system

Consider a system of $N$ particles obeying classical statistics, each of which can have energy $0$ or $E$. The system is in thermal contact with a reservoir maintained at a temperature $T$. What will ...
1
vote
1answer
46 views

Textbook Wave Example Clarification

My textbook gives the following wave example: $$\psi(y, t) = (0.040)\sin\left[ 2 \pi \left( \dfrac{y}{6.0 \times 10^{-7}} + \dfrac{t}{2.0 \times 10^{-15}} \right) \right]$$ It then claims that (1) ...
1
vote
0answers
24 views

Electric field due to non-concentric spherical cavity in a non-conducting charged sphere

I am unable to grab the concept of electric field due to non-concentric shells . Like in case of concentric shells , for example if we consider a solid shell with outer radius 'R' and inner radius 'r' ...
3
votes
6answers
160 views

Does the force of friction helps us to accelerate while running? [closed]

The question is to find the correct statement: Cause of increase in kinetic energy while running is due to the work done by friction force without which he cannot run. OR Cause of increase in kinetic ...