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
49 views

How to find this very $G^{\mu\nu}$?

I am reading the book Supergravity. In chapter 4, section 4.3.2 Duality for gauge fields and complex scalar: The simplest case of electromagnetic duality in an interacting field theeory occurs ...
0
votes
2answers
38 views

Potential difference inside charge distributions

Always when I think about potential difference inside a symmetrical charge distribution, I think of it being equal to zero because it's dependent on the field and I imagine the directions of each of ...
3
votes
2answers
91 views

Is Marshmallow solid or liquid?

A marshmallow is a sugar candy that, in its modern form, typically consists of sugar, whipped to a spongy consistency, molded into small cylindrical pieces, and coated with corn starch. Link ...
-5
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2answers
21 views

Electrostatics question cbse 2015

''The outward electric Flux due to charge +Q is independent of the shape and size of the surface which encloses it.'' Give two reasons to justify this statement.
0
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2answers
30 views

Question on heat

Is this statement correct? The oxygen and nitrogen molecules in a box has equal average kinetic energy but the oxygen molecules are faster. I am not sure because I thought oxygen molecules should move ...
-2
votes
0answers
11 views

Sliding ladder kinetic energy in generalised coordinates [on hold]

This is a problem from Hand and Finchs' Analytical Mechanics, in a chapter looking at holonomic constraints and generalised coordinates in Lagrangian Mechanics. A ladder of length $L$ and mass $M$ ...
-2
votes
0answers
41 views

Proof of definitions of scalar product

I am looking a problem (no 1.7) from the first chapter of book classical mechanics by John Taylor. I have spent so much time but can't find solution how to relate the definition of scalar product. ...
-1
votes
1answer
26 views

A question involving the nuclear radius of two isobars

It is a problem from introduction to nuclear physics- by krane, chapter: nuclear properties, problem 7. It goes like this: From the known masses of $_{~~8} ^{15}\rm O$ and $_{~~7}^{15}\rm N$, compute ...
0
votes
0answers
29 views

Find distance vs. time for a space ship moving through cloud of dust of uniform density

Here's a problem: We have a cylindrical spaceship with cross-sectional area $A$ moves through a stationary cloud of dust of uniform density $\rho$. Initially the ship has some speed $v_0$ and some ...
0
votes
0answers
19 views

Magnetic field due to long current carrying conductor at a point near its end [duplicate]

How can one show that the magnetic field due to an infinite long current carrying conductor (length a) at a point near its end is given by $$B = \frac{\mu_0I}{4\pi a}$$ using Ampere's Circuital ...
1
vote
1answer
27 views

Time for two relativistic objects to meet

How do you prove that the time for two objects traveling towards each other at relativistic velocities is still d/(v1+v2). Answer seems to have something to do with velocity addition but I'm ...
-2
votes
0answers
20 views

3 point masses;circumference [duplicate]

3 gravitating mass points of mass m are on the circumference of a circle with the same distance r to each other. At $t=t_0$ one lets go of the mass points and each of them moves within the ...
-1
votes
1answer
36 views

Dirac field creation and annihilation operators [on hold]

i have to prove the following equations. Can someone give me a hint please?
0
votes
0answers
34 views

Changing the melting point of ice

Myself and a friend have been stuck on this problem for a while now. We know that we should end up with an answer of $-0.007K$ however, cannot get to this solution. Help with the method we should use ...
0
votes
1answer
50 views

Can't derive FRW Christoffel symbol

I'm trying to confirm that the $\Gamma^1_{01}$ Christoffel symbol of the FRW metric is $\dot{a}/a$. I have the FRW metric: $$ds^2=-dt^2+a(t)^2\left[\frac{dr^2}{1-kr^2}+r^2(d\theta^2+\sin^2\theta\ ...
0
votes
2answers
28 views

Yaw angle calculation for a two-wheeled inverted pendulum

[Sorry, if this is a basic question. I'm a software engineer, learning mechanical engineering concepts by trying to build a self-balancing robot] I'm unable to understand the yaw angle equation: ...
0
votes
0answers
14 views

Two charged rods placed along the x and y axis respectively [on hold]

Two charged rods of equal length $L$, $OA$ and $OB$, are placed along the $x$ and $y$ axis, respectively, $O$ being the origin. The rod $OA$ has a charge $+Q$ while the rod $OB$ has a charge $-4Q$. ...
0
votes
1answer
37 views

What does this problem about lenses really want?

This is the problem: The distance between the lens of a simple remote camera (means it's not used to take pictures of close things) and the film is 40mm. how much should we move the lens to get ...
0
votes
1answer
23 views

A solid non-conducting sphere of radius $R$ carries a non uniform charge distribution [on hold]

A solid non-conducting sphere of radius $R$ carries a non uniform charge distribution with charge density $ ρ = k r/R$, where $k$ is a constant and $r$ is the distance from the center. Show ...
0
votes
3answers
23 views

A charge $Q$ is placed at a distance $a/2$ above the center of a horizontal square surface of edge $a$ [on hold]

A charge $Q$ is placed at $a$ distance $a/2$ above the center of a horizontal square surface of edge $a$, while a second charge $Q$ is placed below one of the vertices of square. Find the flux of ...
-3
votes
0answers
45 views

Mechanical energy? [on hold]

A particle of mass $2\,\mathrm{kg}$ is attached to one end of a model spring that is hanging vertically from a fixed point O. The spring has stiffness $4$ and natural length $1\,\mathrm{m}$. ...
1
vote
0answers
29 views

Potential (which only depends on the length of a position vector) [on hold]

a) A potential $U$ only depends on the length $r=|\vec{r}|$ of the position vector $r$. Show that $$\vec{\nabla}U(r)=U'(r)\frac{\vec{r}}{r}. $$ What properties does this vector field have? ...
-2
votes
0answers
50 views

Gravitating masses on a circumference [on hold]

3 gravitating mass points of mass m are on the circumference of a circle with the same distance r to each other. At $t=t_0$ one lets go of the mass points and each of them moves within the ...
-1
votes
1answer
29 views

Velocity of a car in circular circuit

Prior apology for any violation of rules and regulation and poor expression of question. Statement: A racing car moves along a circular circuit with a constant speed of $20\text{ms}^{-1}$ in 5 ...
0
votes
0answers
28 views

How do I calculate the energy flux for this toroid?

My question is how do i calculate the total energy flux through the walls of the torus in this situation? The Poynting flux is given by $\vec{N} = \frac{1}{\mu} ( \vec{E} \times \vec{B})$ but the ...
0
votes
0answers
37 views

Distance travelled by boat! [on hold]

It's kind of silly to ask this kind of simple question of vector, but just wanted to make sure my method of answering is correct. (Sorry for the poor question expression.) Here's the question: ...
0
votes
2answers
40 views

How can we prove that electric field originate from and terminate on charge using Gauss Law?

We already know that electric field originate and terminate on charge only and they doesn't make any closed path. But is it possible to prove this statement using Gauss Law ? If yes then how ?
0
votes
2answers
34 views

String wrapping around a motionless cylinder

A particle is connected to the end of a thin, weightless string, which has its other end connected to the cylinder, in such a way that motion of the particle causes the string to wrap around the ...
2
votes
3answers
41 views

Parallel-plate capacitor working voltage $V={Qd\over{\epsilon_0 A}}$ relationship with plates' distance

I don't understand why the working voltage of a capacitor increases with the plates' distance. Suppose we have 2 capacitors in series where $C_1=12,0\mu F$ and $C_2=4,0\mu F$. The voltage over both ...
0
votes
1answer
35 views

Angular momentum & Energy using Yukawa's potential

I was doing my Gravitation problems and I found this one that I'm unable to solve. Yukawa's theory for nuclear forces states that the potential energy corresponding to the attraction force ...
1
vote
1answer
62 views

Electric field of two infinitely long and thin, straight wires

I know the formula of the electric field, however: suppose that we put two infinitely long and thin, straight wires symetrically into the coordinate system, so that y axis is between them. Now ...
2
votes
1answer
27 views

When does light reach a shell observer in Schwarzschild metric?

I am trying to simulate the trajectory of light in the Schwarzschild metric (as seen by a far away observer) with fixed $\theta = \pi/2$. According to my source (Chapter 18, section 18.5) the ...
0
votes
0answers
26 views

Electric Flux through cube [on hold]

There is a cube with a charge at one of it's vertex(say A). What is the total electric flux and the flux through each face? I know the answer but not the solution. I don't think gauss law would help ...
2
votes
1answer
83 views

Angular momentum - proof for integer eigenvalues

I am confused about a proof my Quantum Mechanics textbook has left "as an exercise for the reader". So, we've got the angular momentum operator $\hat{L}$. We've also got the generalized angular ...
1
vote
0answers
28 views

Changing variables in a Lagrangian to obtain mass terms of gauge fields [on hold]

Context: In a excercise, consider a SU(2) gauge theory. The Lagrangian of the theory contains the three gauge fields and some scalar matter fields: $\phi_1 , \phi_2$ form a SU(2) doublet (fundamental ...
-1
votes
0answers
9 views

Injective parametrization of a curve which is piecemeal $C^1$. [migrated]

$\gamma:$[0,1]$\to R^2$ is an injective parametrization of a curve $\Gamma$, which is piecemeal $C^1$ and the length of the curve is $L(\Gamma_k)<\infty$. 1.1.: Show that for every $n\in N$ there ...
0
votes
2answers
27 views

Area Moment of Inertia about y axis of i Beam [on hold]

I was wondering if anyone could give me some input on what I am doing wrong here, because it is driving me crazy. I am trying to calculate the area moment of inertia about the y axis of this I beam: ...
0
votes
0answers
19 views

surface tension force problem [on hold]

SO i was solving some surface tension problems and got stuck on this one: To determine water surface tension coefficient pipette is used with a hole of 2mm. Through pipette drips 20 water drops with ...
-1
votes
0answers
54 views

A General Relativity question? [on hold]

The line element for the outside of a spherical star\black hole is given by the Schwarzchild line element : $$-c^{2}d\tau^{2} = ds^{2} = -\left(1-\frac{2m}{r}\right)c^{2}dt^{2} + ...
-1
votes
0answers
21 views

Killing vectors of AdS space with the metric given in Poincaré coordinate [on hold]

I am trying to solve this problem: Find the Killing vector correspond to the symmetry of the scale invariant for the AdS(n+1) $$ (t,{\bf x}) \rightarrow (at, a{\bf x}) $$ when the metric of the AdS ...
0
votes
0answers
38 views

Special relativity question [on hold]

I have a problem. I´m trying to solve this, but I have no idea how to start, how to understand it. We have two objects moving away from each other, each has a speed $v$. We measure time in the system ...
-1
votes
0answers
23 views

Commutator relations for bosonic annihilation/creation operator [duplicate]

Does anyone know the commutator: $[a^n,(a^{\dagger})^n]=?$ where $[a,a^\dagger]=1$. I do not need a calculation, the solution is enough.
0
votes
2answers
64 views

Calculating the Precession

This is the Anti gravity wheel video from Veritassium. I have a similar problem to calculate the forces on arm. How can I calculate the precession force pushing the arm vertically ? Lets assume ...
0
votes
1answer
40 views

Maximum range of projectile from elevation, simply?

Let us say you have project a ball at velocity $u$ from a cliff hight $h$, and we want to find the maximum range of the ball. Ok so you could do this using equations of motion (for constant ...
-3
votes
0answers
20 views

Center of Mass of a meter stick before and after an applied force. Find the mass [on hold]

A meter stick balances horizontally on a knife-edge at the 50.0 cm mark. With two 5.40 g coins stacked over the 24.6 cm mark, the stick is found to balance at the 47.0 cm mark. What is the mass of ...
-1
votes
3answers
85 views

Why does the resistance halve when two resistors of equal resistance are in parallel? [on hold]

This is the question and answer to a homework question and I do not understand why this is the case. What is the logic behind it?
0
votes
0answers
27 views

Simple Harmonic Motion Mass and Amplitude [on hold]

You (mass m1 = 77.5 kg) stand on a platform of mass m2 = 21 kg. The platform executes simple harmonic motion with a period of 2.55s. WHen the platform is at maximum displacement, you step off the ...
0
votes
1answer
36 views

What is the distribution of charge on two conducting spheres?

There are two conducting spheres of charges $Q_1$ and $Q_2$ and respective radii of $r_1$ and $r_2$ with center-to-center separation of $L$. Can the distribution of charge on each of the conducting ...
0
votes
2answers
24 views

Doping a Semiconductor with Acceptors [on hold]

I had a question about semiconductors from an engineering class that I am struggling to understand. We were supposed to read the material on our own but it's not clicking for me. I would appreciate if ...
0
votes
1answer
21 views

Inductance of two parallel wires

I've been asked to calculate the inductance per unit length for two wires or radius $a$ separated by $2d$ where $2d>>a$. Starting from $\int_{s} B.dS = LI$ Im not sure what surface to take? ...