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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31 views

Vector Addition and Gravitational Forces

I was given the following question in my Physics class :- Four particles of masses m, 2m, 3m and 4m are kept in sequence at the corners of a square of side a. What will be the magnitude of the ...
1
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0answers
25 views

Use Cartan subalgebra in spinor representation to find weights of vector representation

For $SO(2n)$ we can construct the lie algebra elements by using antisymmetric combinations of $\gamma_\mu$ which obey the Clifford algebra. Up to some prefactor the elements $ S_{\mu \nu} = \alpha ...
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0answers
12 views

Generators of cubic group: Euler angles

I am trying to build numerically all members of the cubic group in the representation of Wigner D matrices. Angular-momentum quantum number may be small, e.g. 2, so I use the formula stated e.g. at ...
1
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2answers
30 views

Free body diagram for two masses on inclined plane with frictions

I'm a bit confused about free body diagrams on inclined planes with frictions. Consider the situation in the picture, where $A$ and $B$ slide togheter on a inclined plane and I want to find a force ...
-1
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0answers
26 views

A body thrown upwards with some external force [on hold]

A ball of mass of $1Kg$ is held in hand. The moment it is released from hand, without any delay it is hit by an external force of $100N$ in upwards direction. How high will the body go ? If we ...
-2
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0answers
24 views

Freely falling body applied some external force [on hold]

A body of mass $10kg$ is thrown upwards with initial velocity = $10m/s$. Then it moves up and falls back down at the same point, after which an external force of $10N$ is applied in the upward ...
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0answers
21 views

Find the angle of the projectile [on hold]

Given: Hmax = 2 * Range Find the angle of the projectile. After using the formula for both Hmax and Range, I got an angle of 74.69 if I am not mistaken. On the math exam teacher said the answer ...
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0answers
31 views

Man on a rotating platform

A platform rotates in counterclockwise with angular velocity w. A man walks from the center of the platform to the border with constant radial velocity v' wrt the platform. $\mu_s$ is the ...
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0answers
19 views

Canonical Transformation [duplicate]

How can I prove that the following transformation is canonical: $\begin{cases}\overline{q}_i=\dfrac{q_i}{Q} \\ \overline{p}_i=Qp_i-2Pq_i \end{cases},\ i\in\overline{1,n}$ where $Q=\sum_{i=1}^n ...
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1answer
29 views

Time-Evolution of a Spin-1 Particle in a Magnetic Field

A spin-1 particle with charge $q$ and magnetic moment $\vec{\mu}=\frac{gq}{2mc}\vec{S}$ is situated in a magnetic field $B=B_0\vec{z}$. At $t=0$ the particle is found in an eigenstate $\hat{S}_y$ with ...
1
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2answers
48 views

When does travelling at a fraction of the speed of light appear to the traveler as if they're going the speed of light? [on hold]

If a spaceship is travelling to Proxima Centari, there is a fraction of the speed of light that would make the spaceship appear to reach Proxima Centauri in four years' time. What fraction of the ...
1
vote
1answer
36 views

Figuring out the orientation of a dipole and its distance from a point charge

The problem assigned is this: A dipole is centered at the origin of a coordinate system, and a small charged sphere is some distance away along the perpendicular bisector of the dipole. The particle ...
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1answer
82 views

Euler's laws - derivation

It looks simple and maybe is easy, but I don't get it. How to obtain the second equality from the first one below? Source: http://emweb.unl.edu/NEGAHBAN/EM373/note19/note19.htm They took ...
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2answers
36 views

Free body diagram with forces of friction

I'm reallizing that I'm very confused on how to make a free body diagram of forces in some situations where there is friction between two objects. I'll make an example where I cannot figure out what's ...
-1
votes
0answers
30 views

Direction of a rectangular vector in two dimensions [on hold]

Assuming the following position vector; R(t) = (2+.4t^2)i + (1.0t)j The function provided yields a parabola, how can I find the specific point in which the angle for the position vector evaluated in ...
-1
votes
0answers
31 views

Determining focal length and positions of principal planes

I have been stuck on this problem for a few days now, and I am still not confident which approach to take with this question. I am consider using the Gullstrand Equation, but I hear some of my ...
1
vote
1answer
29 views

Help to solve a circuit with capacitor and resistor

Till now I'd never solved a circuit with resistor and capacitor. I'd seen the problem and tried to solve. But now I am in a doubt.The circuit was like that- My attempt-
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0answers
17 views

What is frequency response of vibrating string?

If I transform wave equation for vibrating string Mx′′+Cx′+Kx=b(t) in linear system using $x_1(t)=x(t)$ and $x_2(t)=x_1^{'}(t)$ vibrating string equation becomes $Md_tx_2(t)+Cx_2(t)+Kx_1(t)=b(t)$. ...
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0answers
22 views

1D Harmonic Oscillator: Eigenstate (|x=0>) at position x=0

Given an harmonic oscillator I need to calculate the eigenvector $|x=0\rangle$. Knowing that $$x|x=0\rangle = 0 \quad \Rightarrow \quad (a + a^\dagger) | x = 0 \rangle = 0 $$ I started to plug in the ...
-5
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0answers
60 views

Resistance is given as mentioned how will we find the equivalent resistance dnt think anyone can do it [on hold]

it is a electric circuit do we have to use ohms law for this question if yes how will we do it
-2
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1answer
50 views
-1
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0answers
49 views

Show that function $F$ is a constant of motion for a Lagrangian [on hold]

Function $$F=(\dot{z}R-z\dot{R})\sin\varphi-zR\dot{\varphi}\cos\varphi$$ should be a constant of motion for the Lagrangian $$ ...
-1
votes
1answer
53 views

Relative velocity of a boat traveling on a river [on hold]

I am confused about relative velocity. So suppose a boat is traveling upstream on a river and a crate is dropped overboard. The boat continues to travel upstream for 60 minutes and reaches a ...
4
votes
3answers
106 views

Which force to resolve?

In the above image the particle is effectively moving 'out of the page' in circular motion. We want to solve for $\alpha$, the slope is smooth, and the particle is moving neither up nor down the ...
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4answers
43 views

how is a pendulum clock's time and the time period of the pendulum in it related? [on hold]

I'm working out how much time a pendulum clock will gain or loose due to change of the length of the pendulum due to temperature. so far I've got, new time period, $$T_2=T_1(1+\frac12\alpha\Delta T)$$ ...
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0answers
41 views

Landau levels in uniform magnetic field

Intro Landau levels are obtained by gauging the vector potential to be $$ \vec{A}=\left(-By,0,0\right) $$ By which the Hamiltonian: $$ H={1\over 2m}\left(\vec{p}-q\vec{A}\right)^2 $$ can be ...
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0answers
24 views

Problem in electrostatics [on hold]

I tried a problem in electrostatics. In which I emplyed two different methods to find the electric field inside a solid cylinder of charge distribution having density ...
0
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1answer
18 views

How do I show for an ideal transformer $M^2=L_1L_2$?

I've been stuck on this problem for about an hour. In an ideal transformer, the same flux passes through all turns of the primary and of the secondary . Show that in this case $M^2=L_1L_2$, where ...
-2
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0answers
24 views

Gauss law-electric field through the spherical surface of a sphere [on hold]

FIND THE WORK DONE IN MOVING A POINT CHARGE Q=10 MICROCOULOUMBS FROM THE ORIGIN TO A POINT(4,pie/4,pie/2)SPHERICAL COORDINATES IN THE FIELD E=5e^(-r/4)+10/(rsinx)
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votes
2answers
41 views

Work-Energy Problem

A wire, which passes through the hole in a small bead, is bent in the form of quarter of a circle. The wire is fixed vertically on ground as shown in the figure. The bead is released from near the top ...
0
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1answer
50 views

Special Relativity problem - proper time interval

The supernova 1987A explosion in the Large Magellanic Cloud 170 000 light years from Earth produced a burst of anti-neutrinos ν ̄e which were observed in terrestrial detectors. If the anti-neutrinos ...
-1
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0answers
39 views

Find Time it Takes For an Object in Free Fall To Hit Ground With Given Gravity [on hold]

Sorry if this seems like a simple question. I'm not that good with physics but I'm willing to learn! So my question is, how can I find the time it takes for an object at "h" height to hit the ground ...
-1
votes
1answer
64 views

If the Earth were a pool ball, could I feel mountains? [on hold]

If the earth (12,742 km diameter) were scaled down to the size of a pool ball (61mm diameter), the mountain ranges would still exist, obviously. But would a typical human be able to feel those ...
1
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0answers
40 views

What is the path taken by a “cable car”?

A well known result in variational calculus & Lagrangian Mechanics is the solution to the "brachistochrone" problem, where it is found the path connecting two points, A & B such that the time ...
1
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0answers
35 views

Magnetic field of one electron

I want to reproduce a calculation of the magnetic field at the atomic nuclei produced by one electron in hydrogen: Maxwell gives us: $\vec \nabla \times \vec B = \mu_0 \vec j$ Doing the surface ...
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0answers
35 views

m1v(initial) +m2v (initial) = m1v (final) +m2v(final) [on hold]

Perfectly elastic collisions. Imagine two billiard ball on the table. Ball A has a mass of 2 kilograms and the ball B has a mass of 3 kilograms. the initial velocity of ball A is 9 meters per second ...
0
votes
1answer
31 views

Use of the chain rule in kinematics problems for quantities given in function of the position [on hold]

I don't understand the use and the meaning of the application of the chain rule in some situations. For istance, consider a 2D motion and the equation of trajectory described by a point $y=f(x)$. ...
1
vote
2answers
81 views

Let's consider a sphere of radius $R$ at $T_0=100$ C in a far field of water with temperature $T_\infty=30$ C [on hold]

Let's consider a sphere of radius $R$ at $T_0=100$ C in a far field of water with temperature $T_\infty=30$ C. How to calculate the sphere's temperature in each "layer" at any time? I really don't ...
0
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0answers
31 views

Sign convention in geometrical optics

This is slight misconception that has bugged me. While deriving the mirror formula: $$\frac{1}{u}+\frac{1}{v}=\frac{1}{f},$$ people (as per my reference book) tend to apply the sign convention to ...
0
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0answers
53 views

$\phi^4$-theory perturbation series

I am trying to understand the method of Feynman diagrams in interacting quantum field. I take lagrangian for the $\phi^4$-theory $$\mathcal{L} = \frac{1}{2}\partial_{\mu}\phi\partial^{\mu}\phi ...
1
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0answers
29 views

Hamiltonian for closed strings [on hold]

I am reading GSW volume 1 and it says in chapter 2 that the Hamiltonian for closed strings turn out to be $$ H = \frac{1}{2} \sum_{n=-\infty}^{\infty} (\alpha_{-n}.\alpha_{n} + \tilde{\alpha}_{-n}\cot ...
2
votes
1answer
75 views

Components of dual vectors

(This is a close retelling of Wald, problem 2.4b. Not for homework; just curiosity and an increasingly alarming suspicion that I've never actually understood anything.) Let $Y_1 ... Y_n$ be a ...
1
vote
4answers
148 views
+50

What will be final velocity of three charges $q$, $q$, $2q$?

What will be final velocity of three charges q, q and 2q kept along an eqilateral triangle of side r at infinite distance. All three masses are equal. I tried to conserve Total Energy ...
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votes
1answer
36 views

a problem on circular motion [on hold]

Question:A cyclist is riding with a speed of $7.5$ m/s. As he approaches a circular turn on the road of radius $80m$, he applies brakes and reduces his speed at the constant rate of $0.50$ m/s every ...
0
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1answer
36 views

Parallel plates with differing charges

I'm given a problem involving two parallel conducting plates a small distance apart. One has charge Q, the other is neutral. I'm asked to find the surface charges on all faces. I began by ...
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0answers
50 views

Science question [on hold]

imagine two billard balls on a pool table A ball has a mass of 2 kilograms and ball B has a mass of 3 kilograms. the initial velocity of ball A is 9 meters per second to the right and initial velocity ...
3
votes
1answer
100 views

How I can prove the Commutation between hamiltonian and Runge-Lenz vector? [on hold]

I am a undergraduate student in physics. I found this page that shows a way to prove the commutator between Runge-Lenz vector and Hamiltonian .$\left [\hat{A}_{i},\hat{H}\right]=0$ I believe he did a ...
0
votes
1answer
41 views

Motion of Particle due to Lorentz Force

So my professor gave us the following question: A particle with electric charge $Q$ and mass $M$ is initially traveling with velocity $v_0$ in the $x$ direction at time $t= 0$. There is a constant ...
-2
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0answers
38 views

What is the electrical potential at point A, 15.4 cm from the center of the charge? [on hold]

I am simply looking for a place to start or a correct formula to use. Physics isn't my strong suit so if I could just get a lead then hopefully that will help. I've tried the electric potential ...
0
votes
1answer
46 views

Divergence of inverse of metric tensor

I know that the Levi-civita connection preserves the metric tensor. Is the divergence of the inverse of metric tensor zero, too?! I'm not so familiar with the divergence of the second ranked tensor. ...