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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1answer
20 views

Kittel solid state physics handbook - Plasma oscillation of a ball - Am I solving this right?

I'm self learning nanotechnology undergraduate and I'm trying to solve a problem from chapter "plasmons, polaritons and polarons". This is it: Frequency of uniform mode of plasmons in a ball is ...
-5
votes
3answers
35 views

Net force of the following? [on hold]

The following objects are attached to one another and have difference force directions: Where is the direction of force? And What is the net force? I'm trying to calculate it using their angles, ...
0
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0answers
32 views

Electromagnetism Boundary condition

The dielectric slab surrounded by air as shown in diagram has permittivity $\epsilon$ different from air and permeability almost same as air. Electric field everywhere within the slab is given to be ...
0
votes
1answer
30 views

Gravitation - hole to center of Earth [on hold]

Question: Assume that a tunnel is dug across the Earth (radius = $R$) passing through its centre. Find the time taken for a particle to reach the centre if it is projected into the tunnel from the ...
1
vote
1answer
45 views

Prove the relation between relative velocity ,momentum and energy

In Chapter 8 of F.Mandl's book Quantum field theory, during the derivation of the differential cross section, the following relation is used: $$E_1E_2v_{rel}=\sqrt{(p_1p_2)^2-m_1^2m_2^2} \,\, ,$$ ...
0
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1answer
32 views

A falling steel beam - Maximum induced voltage [on hold]

I'd appreciate it if someone could explain how to answer this question: A 2 m long steel beam is falling from a height of 12,5 m. During the fall, the beam is oriented in an east-west direction. ...
-2
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0answers
18 views

Are these Kinematics Equations Correct? [on hold]

Can someone make sure that these kinematic equations I derived are accurate please? Thanks in advance. I'm new to this forum, so if I'm doing something wrong, let me know. I understand the below ...
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0answers
25 views

Lorentz transformations of spinors in $SL(2,\mathbb{C})$

I was wondering what the matrix representations of all the coordinate rotations and Lorentz boosts of the $SL(2,\mathbb{C})$ were along with a general method of solving for them. I've been able to do ...
-2
votes
0answers
28 views

FINDING THE ANSWER [on hold]

Equiptment- Micronair air barrier sprayer (60 gal tank) Output Rate-2 gal/min Swath width-6 feet Product demand CS Rate 5 oz/1000 1, square feet is 22225 sqft 2.How many gallons of mix will we ...
-1
votes
1answer
33 views

Center of mass finding question [on hold]

Find the center of mass the rod in the figure if λ (the mass per unit lenght) varies with $x$ according to $\lambda=dm/dx=\beta x^2$, where $\beta$ is a constant. Sorry for quality of picture. I am ...
0
votes
1answer
96 views

Confusion with anti-symmetric tensors!

I want to prove the following fact for two antisymmetric tensors: $$ 2G^{+\rho (\mu} H_{\,\,\, \rho}^{+\nu)} = -\frac{1}{4}\eta^{\mu \nu} G^{+\rho \sigma}H_{\rho \sigma}^{+}. $$ When I try to do it I ...
0
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0answers
44 views

How fast would a 60 km diameter moon ring rotate to simulate 1 G? [on hold]

After seeing this answer regarding increasing mass for greater weight on the moon, my eyes caught the first comment about centrifuges in science fiction. Naturally, the thought of putting Elysium on ...
1
vote
1answer
49 views

Symplectic notation proof?

Hello I am trying to work through a little proof of the symplectic condition for Hamilton's equations for a classical mechanics course. I am trying to understand the meaning of the relation ...
0
votes
0answers
8 views

maximum dislacement on dumping sistem with FDM [on hold]

A precision grinding machine is supported on an isolator that has a stiffness of 1 MN/m and a viscous damping constant of 1 kNs/m. The floor on which the machine is mounted is subjected to a harmonic ...
2
votes
1answer
67 views

Relativistic Kill Vehicle

What would happen if a significantly supra-molecular object (say ranking from grams to low kilotons) would be accelerated to relativistic speeds (>.10 c) such that its worldline would intersect with a ...
0
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0answers
54 views

Understanding the physical applications of the Laplacian: Finding the heat-equation using the continuity equation [on hold]

I know the following: $$q=\rho c T$$ Where $q$ is heat per unit of volume, $\rho$ is the density, $c$ is the specific heat capacity and $T$ is the temperature. The flow of heat is given by: $$\vec ...
-2
votes
0answers
25 views

Block slides down smooth hemisphere: WHEN will it leave surface? [on hold]

A block is at rest at the top of a frictionless hemisphere of radius r. It is slightly disturbed and starts sliding down. WHEN will it leave the surface of the hemisphere?
0
votes
1answer
26 views

Position of Centre of Mass [on hold]

Prove that: $$\vec{R}_{CM} =\frac{\sum_{i=0}^n M_i\times \vec{R}_i}{\sum_{i=0}^n M_i }$$ Where, $\vec{R}_i$ and $M_i$ are the position vector and the mass of $i^{th}$ particle in the system ...
0
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0answers
28 views

Difficult Atwood's machine problem - Finding $L(t)$ [on hold]

The whole problem was: You have got a turnable disc of mass $m$ and radius $r$. The rope around the disc has mass $M$ and length $l$. At time $t=0$ the disc is not turning. The height difference ...
-1
votes
1answer
25 views

Torque and Moment [on hold]

pole vaulter holding a vaulting pole parallel to the ground. the pole is 5 metres long. vaulter grips pole with right hand 10 cm from the top end of the pole and with his left hand 1 metre from the ...
-3
votes
1answer
36 views

Jets of equal height from a pipe

Lets say I have a pump that delivers some flow and pressure to a horizontal pipe with holes at different location. Let's say L=0.5 m, 1m, 2m etc... The question is: What should the diameters of these ...
2
votes
0answers
40 views

Euler-Lagrange equation (equation of motion) solution with hairy Lagrangian [on hold]

I'm going through Zwiebach Chapter 6 on relativistic strings to try to solve a similar problem. I got all the way to my equation of motion \begin{eqnarray*} \delta S & = & [ p' \delta ...
0
votes
1answer
24 views

Spin Hilbert space

I'm currently doing some quantum mechanics and was able to transform my Hamilton operator to something that basically looks like this: $$ H = H_{xy} + \frac{p_z}{2M} + \alpha S_z, $$ where $H_{xy}$ ...
0
votes
1answer
24 views

Heat of Vaporisation - Enthalpy [on hold]

Hey guys I came across a question and I'm just wondering if my method is correct because the answer at the back of the book is different. Question The entropy of water at atmospheric pressure and ...
3
votes
3answers
115 views

Derivation of the speed of light using the integral forms of Maxwell's Equations

Having just finished physics 2, I've been (slightly) exposed to showing that light is a wave with speed $1/\sqrt{\mu _0 \epsilon _0 }$ using the differential forms of Maxwell's equations, though this ...
-2
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0answers
5 views

how to calculate the frequancy and impulse response of the photodiode-detector [migrated]

can you help me to do the problem ( some hints how to solve those problems based on experimental method course)
-1
votes
0answers
17 views

Projectile Motion with uneven ground [duplicate]

I am suppose to find the optimal angle $\theta$ for a stone to be thrown with the initial velocity $u$, from a tower, of height $h$ to obtain a maximum distance (Range) $R$. So I did the some ...
0
votes
1answer
27 views

cross over to another object that has same height with our last position, is that really possible?

I have got confused with this. Well..In that picture, lets say the height is 8m, and the car moves and going to cross over to another object that has the same height with its last position..my ...
1
vote
0answers
52 views

Getting the electric field using Green's function [on hold]

Let the Green's function for the gauge field be given (after gauge fixing) as $$G_{\mu \nu}(x,y) = \delta_{\mu \nu}G(x-y) \tag{1}$$ where $$G(x-y)= \int \frac{d^dk}{(2\pi)^d} \frac{e^{ik \cdot ...
1
vote
0answers
27 views

Describing the motion of a point-mass [on hold]

Consider a point-mass moving around a fixed point on a circle with radius $r$ with constant angular velocity $\omega$. At a certain moment of time, the connection is removed, and the point-mass flies ...
4
votes
1answer
64 views

Conformal Killing fields on Schwarzschild

I am trying to understand which are the conformal Killing Fields on the Schwarzschild spacetime. I say that $X$ is a conformal Killing field on $S$ ($S$ is Schwarzschild) if there exists a function ...
0
votes
1answer
39 views

Jumping off a boat vs ship [on hold]

Why it is harder to jump towards the coast in a boat than in a ship (more massive than the boat) that is equally near as the boat? I think we should use Newton Law's and this happens because the mass ...
1
vote
1answer
38 views

Understaning Euclidean Green's function

Consider a scalar field coupled to a source $$(\Box - m^2)\phi(x) = -J(x)\tag{1}.$$ Then, the response of the source is determined by the Green's function $G(x-y)$, which satisfies $$(\Box - ...
1
vote
3answers
98 views

Calculate the rise in temperature from directed radiation [on hold]

For example I have a 1 watt laser and direct it to a sheet of metal (copper), if I were to direct it for say a time interval of 1 minute what would be the change in temperature? I can predict that it ...
1
vote
1answer
43 views

What is the motion of a balloon with a person climbing on a ladder?

Suppose you had a balloon of mass $M$ in the atmosphere at rest relative to the ground, with a ladder attached reaching towards the ground. A person (of mass less than $M$) begins climbing up the ...
0
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2answers
26 views

Tension of 2 massless springs joined together

A cable is formed by joining two massless springs with different spring constants. Spring A has constant k1. Spring B has constant k2. If mass M1 hangs from the cable, is the tension greater on ...
-1
votes
1answer
26 views

Understanding tension principles in a 2 pulley system [on hold]

Trying to understand tensions in a 2 pulley rope system, where M1>M2. Is it true that T1>T2>T3?
2
votes
1answer
34 views

Different results for displacement using different Kinematics equations

We drop an object from a height. It displaces a distance $L$ in the $\vec{y}$ direction. So: $$ L = \frac{1}{2}at^2 $$ Or: $$ v^2-v_0^2 = 2aL \rightarrow L = \frac{v^2}{2a}$$ How much would the ...
1
vote
2answers
57 views

Proof that quantum Fourier transform is unitary

I'm trying to work through the proof that the quantum Fourier transform can be described by a unitary operator, i.e $F^{\dagger}F=\mathbb{1}$, where ...
0
votes
0answers
22 views

Moment of Inertia of Rectangular Body about a diagonal axis [on hold]

The rectangular plate has a mass M and breadth 'r' and length 'l'. What would be the moment of inertia of the body along the given axis (parallel to the diagonal)?
2
votes
3answers
62 views

Torque for a door

The question is: A door is hinged at one end and is free to rotate about a vertical axis. Does its weight cause any torque about this axis? Give reason for your answer. I think that the answer ...
0
votes
0answers
17 views

Capacity of rain water down pipes [on hold]

How to calculate the capacity (m3/sec) of a vertical down pipe, with a certain diameter and a certain height if at the bottom, the pipe turns certain degrees and then after a certain length of the ...
0
votes
0answers
14 views

Prism formula base question [on hold]

An equilateral prism has a refractive index of $\sqrt{3}$. A ray of light is traveling parallel to base of the prism. What is angle of incidence?
0
votes
0answers
41 views

Mean size of a Cooper pair [on hold]

I'm having some difficulty with a the calculation of the means quadratic average distance between two electrons of a cooper's pair. I have: $$\Psi(\vec{r}) = \int d^3 \vec{k} e^{i\vec{k} \cdot ...
1
vote
0answers
38 views

Partial Integration of outer product of del and position vector

I am trying to understand the solution I have been given to prove the following relation for a current density $\vec{j}(\vec{r})$ that is concentrated around the origin: $$ \int_V dV \, ...
-1
votes
0answers
26 views

Determine a gradient field [on hold]

Given the following field of force, $$ \vec F(\vec r) =\begin{pmatrix} 2x+2y+az \\ 2x-3ay \\ 4x+c+2z+yd \\ \end{pmatrix} $$ My exercise is to determine $a,b,c$ ...
1
vote
0answers
27 views

Period of a pendulum in a lift going up [duplicate]

So I know that the period of a pendulum in a free falling elevator isn't going to change because there is no force acting on it since $$T = 2\pi\sqrt{\frac{\ell}{g}}.$$ So what happens to a pendulums ...
0
votes
0answers
24 views

Double well potential [on hold]

A particle is in the following double-well potential with $E<0$: $$V(x)=0 \quad for \quad x<-a, x>a; -V_0 \quad for \quad -a<x<-b, b<x<a; 0 \quad for \quad -b<x<b$$ I am ...
2
votes
3answers
72 views

How to calculate the value of gravitational acceleration of my town

We normally consider the value of gravitational acceleration $g = 9.8 m/s^2$ while solving the problem. But that is the value of $g$ at poles (if I am not wrong). My teacher have given as homework ...
0
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0answers
21 views

What affects the period and the frequency of a longitudinal vibration?

In a lab experiment, our objective is to observe the characteristics of longitudinal waves/vibrations. If we changed the mass and amplitude, I feel that they either affect the period and frequency of ...