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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-2
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0answers
24 views

Parallel combination of cells

In this circuit suppose that $E_1 >E_2$. This means that the positive terminal of $E_1$ will have a greater potential than the positive terminal of $E_2$. Then current should flow from the ...
0
votes
0answers
25 views

Swirl velocity from circulation - Vortex

I have a vector field in cartesian coordinate $(x,y)$ with coordinate origin at vortex core. For calculating the swirl velocity $v_\theta$ I followed below steps, Step 1: Find the circle coordinates ...
0
votes
1answer
32 views

Acceleration of a pulley system

The figure above shows a pulley system consisting of 3 masses ($m_1$, $m_2$ and $m_3$), a homogeneous wheel (radius R, mass M) and 2 massless pulleyes which are connected by a massless rope. Mass $m_1$...
-4
votes
0answers
21 views

Motion in one dimension and relative velocity [on hold]

Two bodies $A$ and $B$ are separated by $4~\mathrm{km}$ and $A$ is due west of $B$. If $A$ moves at a speed of $6~\mathrm{km/hr}$ towards the south, what is the relative velocity of $A$ w.r.t $B$?
-4
votes
0answers
14 views

Find the energy of an x-ray photon which can impact a maximum energy of $50~\mathrm{keV}$ to an electron [on hold]

This is an exercise question from the text book Concepts of Modern Physics by Arthur Beiser. Find the energy of an x-ray photon which can impact a maximum energy of $50~\mathrm{keV}$ to an ...
0
votes
3answers
41 views

Invariance of a maximally entangled state under unitary operation $U \otimes U^\dagger$

Apparently the (d-dimensional) maximally entangled state, $|E \rangle = \sum_{i} |ii\rangle /\sqrt{d}$ is invariant under operations of the form $U \otimes U^\dagger$. I want to prove this result, ...
1
vote
0answers
25 views

Derivation of expression for Berry curvature

Many texts quote the expression for the Berry curvature for a two-level system, with Hamiltonian $\mathbf{h}(\mathbf{k})=(h_x,h_y,h_z)$ in terms of $\mathbf{k}=(k_x,k_y)$, as something like \begin{...
1
vote
1answer
43 views

How do you get quantum Hamilton-Jacobi equation from Schrödinger equation? [on hold]

I am reading "The undivided universe: an ontological interpretation of quantum theory" and cannot understand this derivation. Schrödinger equation: $$ i\hbar \frac{\partial\psi}{\partial t} = -\frac{\...
1
vote
2answers
34 views

Does charge of capacitor at constant voltage change after dielectric material is inserted?

I have a planar geometry capacitor, connected to a battery that supplies V volts. Initially there is vacuum/air in between both plates. Afterwards, some dielectric material is inserted in between both ...
-7
votes
0answers
39 views

Interesting question to figure it out [on hold]

A 50-cm-long iron rod is heated from 20 °C to 100 °C. The linear coefficient of expansion for iron is $1.2 × 10^{-5} K^{-1}$. How to determine the change in length of the rod. By which formula?
0
votes
1answer
73 views

Kinematic problem (initial acceleration) [on hold]

A ball is rolling over a soccer field with constant velocity $V_{b} > 0$ at an angle of 45° to the goal line. It starts at the corner of the field (distance $d$ beside the middle of the goal line) ...
0
votes
1answer
25 views

Particle attached in equilibrium to two elastic strings

The question I'm trying to answer is this: This is the solution: The only part of the solution I have a problem with is $x_{ps} + x_{qs}=l$, where $x_{ps}$ is the extension of the string from $P$ ...
3
votes
1answer
254 views

How does the distribution of mass affect gravitational attraction?

For example, if a planet is considered as a point mass, then an object inside the planets' gravitational field experiences an equal attraction from all of the planets' mass. However if the planet is ...
-2
votes
0answers
29 views

Calculation of stone dropping [on hold]

A stone dropped from a building of height $h$ reaches the ground after $t$ seconds in the air. From the building top, if two stones are thrown, one upwards, the other downwards, with same velocity $u$...
1
vote
0answers
53 views

Lagrangian of a coupled pendulum

I am trying to find the Lagrangian for a coupled pendulum: the two pendulums have the same characteristics (length $l$ and mass $m$) and are attached to the same roof at a distance $d$. In addition, ...
-1
votes
0answers
55 views

Linear motion in a constant acceleration [on hold]

a car start to move from rest and travels along a straight horizontal road with a constant acceleration. Velocity of the car after t seconds is vms-1. Find the displacement of the car during the ...
1
vote
3answers
109 views

Finding the Expectation value of harmonic oscillator [on hold]

What is the expectation value for $e^{{\alpha}a^{\dagger}}e^{-\alpha^*{a}}$ of any two states of harmonic oscillator (let say $|n\rangle$ and $|m\rangle$) given below, $$\langle n|e^{{\alpha}a^{\...
1
vote
1answer
49 views

I cannot verify if given transformation is canonical (CT) [on hold]

I'm going on a list of exercises and there's 6 days that I can't figure to this. Prove that given transformation is canonical: $\Large Q=\frac{p}{mw}\sin(\frac{mwq}{P})$; $\Large P=p\cos(\frac{...
1
vote
0answers
44 views

What is wrong with my formulas for a mathematical model of a double pendulum? [on hold]

I tried mathematics but I've had no response in a month. I wanted to create a computer simulation on Matlab, using a model for a pendulum from this study (A double pendulum model of tennis strokes. ...
4
votes
1answer
57 views

Does the force on the bottom piece of a hummingbird feeder depend on the height of the water in the reservoir?

Intuitively I would think that the more nectar you put into the reservoir the more weight it will put on the bottom piece (the tray that holds the open pool of nectar that the birds can feed out of). ...
2
votes
0answers
49 views

Rotation of rod [on hold]

A uniform rod of length "L" is free to move and rotate in gravity-free space . when an impulse is given to one end of the rod perpendicular to its length, its center of mass moves with velocity "V". ...
-2
votes
1answer
32 views

Max weight the lid of a vacuum can hold [on hold]

I have a box with a lid that has a mass object inside of it. I will be creating a vacuum inside of it with a $4~\mathrm{HP}$ Shop Vac that has a sealed pressure of $59~\mathrm{psi}$ and an airflow of ...
2
votes
1answer
44 views

Optimal axis of rotation of a baseball for lateral movement

Suppose a baseball travels at $90\;\mathrm{mph}$; what is the ideal axis of rotation for lateral movement of the ball? (two-seamer or cutter). So far I think that the following factors play a ...
14
votes
1answer
1k views

What are the odds of finding an electron a long way from an atom? As in metres away? [on hold]

Pretty self-explanatory, heard that there is a chance that you might find an electron on the other side of the universe, just wanted to know.
1
vote
0answers
36 views

What is the gravitational field inside a hollow spherical cavity embedded in a solid sphere? [duplicate]

Imagine a solid sphere of radius $R$. From the inside of this sphere we remove a smaller sphere of radius $r$. The sphere can be situated anywhere inside the massive sphere. How does the gravitational ...
0
votes
1answer
36 views

Kinematics of Rectilinear Motion [on hold]

A car leaves an outpost and reaches a speed of $60 m/s$ with a constant acceleration of $3 m/s^2$. It continues at this speed for a time then decelerates at $4.2 m/s^2$. How far will the car be after ...
0
votes
0answers
25 views

Black body emission by a dielectric slab [on hold]

I need to calculate the radiation emitted by a rectangular dielectric slab (glass) at temperature $T_0$. The slab has a thickness $t$, sides $a,b$ and a dielectric constant $n(\lambda)$. How can I do ...
-4
votes
0answers
15 views

a spring is stretched 10mm by a weight of 2.0N calculate the force constant k [on hold]

stretched 0.01metres weight of 2.0newtons calculate force constant k calculate the weight of an object that causes an extension of 80 millimetres
-6
votes
0answers
41 views

Can someone please solve this problem? please [on hold]

Please help me answer this one. I nee the answer as soon as as possible. Your help will be greatly appreciated. Please.. Thank you so much!
0
votes
0answers
62 views

Stress-Energy tensor of a static, spherically symmetric, perfect fluid [on hold]

I am trying to derive the equation for the interior mass of a spherically symmetric, static, perfect fluid in general relativity, $$\frac{\mathop{dM}}{\mathop{dr}} = 4\pi r^2 \rho(r).$$ This question ...
-3
votes
0answers
28 views

Why was the formula (1/3)mL^2(α) used in this problem? [on hold]

I can't tell where this equation is from. Is it the moment of inertia for a rod? If so, it doesn't say so in my physics book. Help please?
-3
votes
0answers
32 views

Why does depth and height replace volume in this problem? [on hold]

In the following problem, why does H/𝛿 replace V/V? The two ratios have different units. Is there something I'm missing here?
-1
votes
0answers
19 views

Thermal radiation [on hold]

The emissivity of a hemi-sphere varies as: $$ e=E\cos\theta$$ What is the ratio of emissive energy between the given sphere and a normal black body sphere.
3
votes
2answers
124 views

Gravitational Strength on a theoretical flat planet

Ok, so let me clarify: a planet that overcame all structural problems with being planetary size, I.E. collapsing into a ball. What would be the gravitational strength on a flat planet with the ...
1
vote
2answers
55 views

Use of $g$ for centripetal acceleration

I have attached an image above including the question I'm unsure of (part B) In a nutshell, a satellite is orbiting Earth at the surface. Given is $g$ and the radius of the Earth. For part bi) the ...
-1
votes
0answers
30 views

What will be the new moment of inertia? [on hold]

Let assume we have a sphere of radius $R$, and we can simply calculate the moment of inertia if we consider the axis is going through the center O. Let's cut a sphere small radius $r$ from the sphere ...
-2
votes
0answers
28 views

Relative motion of a Boat [on hold]

An boat goes down a river in a velocity of 5 m/s relative to the river.At t=0 the man in the boat sees a bottle going down the river.If boat turn and start to return at t=30min, After how much time ...
3
votes
1answer
56 views

Relationship between position and momentum matrix elements

I am going through Faist's Quantum Cascade Lasers book. In the first section of the fourth chapter, he asserts that (in the context of a perturbative analysis of electronic transitions) the ...
-6
votes
0answers
28 views

the quantity of matter contained in a body is the ______ of the body [on hold]

I didn't understand this on my test I think it was mass
-4
votes
0answers
17 views

waves motion and sound and organ pipes [on hold]

in an open organ pipe whose one end is at x=0, the pressure is expressed by P=P0cos(3pi/2)sin(300(pi)t) where x is in meter and t in sec.then the organ pipe can be- a)closed at one end ,open at ...
-4
votes
0answers
115 views

A riddle with a physics related answer [on hold]

This question is from this book which has riddles with answers related to physics. I can't seem to get this one. My origins are humble. I started with a couple of people trying to understand ...
0
votes
0answers
45 views

High School Physics [on hold]

Two girls are standing on a bridge over a river. One girl falls freely and the other ties a rope to her legs. Both jump at the same time from the bridge. The length of the rope is more than the ...
0
votes
3answers
98 views

How much water did I actually drink? [on hold]

Water expands at temperatures over $5^\circ\mathrm C$ strictly monotonic. If you now drink $1~\mathrm{L}$ water ($5^\circ\mathrm C$) which will expand in your body on $37^\circ\mathrm C$, did you ...
0
votes
0answers
21 views

Fierz identity in Spin(5,5) [on hold]

I am trying to understand(derive) equation 3.8 in 1208.5884 which is First, here $\gamma$ is $16\times 16$ chirally projected gamma matrices. which $\alpha=1,2,3,4,...16$ and $a=1,2,3,4,5,6,7,8,9,10$...
0
votes
2answers
55 views

Mass density of a cylinder increasing with the square of the radius

I’ve had to deal with a question like this on a test on friday and I just can’t get it out of my mind. I was supposed to calculate the moment of inertia of a cylinder with an inhomogenous yet ...
-1
votes
0answers
50 views

High School Physics-Electromagnetism [on hold]

An insulated smooth square frame ABCD of side $a$ is able to rotate about one of its side taken as positive axis. The plane is initially located at x-z plane. A magnetic field present in the region ...
-2
votes
1answer
37 views

basic question about work exercise [on hold]

I am learning independently from Tobochnik's statistical physics text. He asks a warm up question about work: A person pushes a block up a frictionless ramp. Is the work positive, negative, ...
-1
votes
1answer
37 views

Horizontal Velocity of a Projectile thrown from a Cliff [on hold]

If I were to throw a rock of a cliff at 12 m/s as a horizontal velocity, what will the final velocity of the rock become when it hits the ground? I am tempted to say 12 m/s because the horizontal ...
0
votes
1answer
45 views

What happens with QM particle at constant velocity? [on hold]

In QM particles have wavefunctions that disperse quite fast. The FWHM for gaussian wavepacket increases in time as $\Delta x(t)= \Delta x_0\sqrt{1+(t/\tau)^2} $, $\tau=2m(\Delta x_0)^2/\hbar$ What ...
0
votes
3answers
103 views

How feasible is it to power your home with a bicycle? [on hold]

This article claims "60 Minutes On This Bicycle Can Power Your Home For 24 Hours!" How feasible is this claim? Sounds great - but the skeptic in me says "yeah, right." Hope this is an acceptable ...