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2
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1answer
16 views

Electric Potential due to Sphere when cavity is at arbitrary position

While doing practice question, I came across a question... A solid sphere of radius a has a cavity of radius b which has a uniformly charge distributed with density $-\rho$ and the remaining part ...
1
vote
0answers
8 views

Bullet - Jet problem, How to equate horizontal displacement. projectile motion [on hold]

A jet is moving hotizontal with speed of 720km/h at height 1960m . when it passes above point on ground at same time bullet is fired from that point with velocity 400m/s I want to know the angle from ...
0
votes
1answer
15 views

Find the magnitude of the resultant force which these engines exert on the rocket?

A rocket fires two engines simultaneously. One produces a thrust of 760N directly forward while the other gives a thrust of 484N at an angle 34.0 degrees above the forward direction. What is the ...
1
vote
1answer
15 views

Determinant of block matrix with off diagonals as vectors

I've been given an $(n+1)\times(n+1)$ square matrix, which is written in the form of a block matrix with the following dimensions $ \begin{bmatrix} (1\times1) & (n\times1)\\ ...
0
votes
0answers
23 views

Why is there not always a force in the direction of motion?

This was a question on a physics competition. A girl throws a teddy bear straight up. Consider the motion of the bear only after it has left the girl’s hand but before it touches the ground, and ...
1
vote
1answer
25 views

$dU = \sum E_i dp_i + \sum dE_i p_i = TdS - PdV \implies \sum dE_i p_i = - PdV$?

This is a formula my professor gave in class, but I'm entirely lost how he arrived at the conclusion (I understand the assumption). Could anyone help me?
1
vote
1answer
14 views

Rutherford scattering: question about impact parameter

http://wonka.physics.ncsu.edu/~blondin/py203/HW5solns.pdf I have a question about the solution to a problem I found online. I don't understand why the author plugs in $\theta=90$ when the question is ...
-1
votes
1answer
17 views

Vectors finding direction include the difference between “north of east” and “east of north”

In what direction is your friend from the starting point after skiing 3 km east and then 1.5 km north? so far I know that angle= tan-1(opp/adj)=(1.5/3.0) angle= ...
0
votes
1answer
37 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 ...
2
votes
0answers
29 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 ...
0
votes
0answers
15 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
vote
2answers
32 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 ...
0
votes
0answers
28 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 ...
-1
votes
0answers
26 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 ...
1
vote
0answers
23 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 ...
1
vote
0answers
33 views

Man on a rotating platform [on hold]

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 ...
1
vote
0answers
21 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 ...
0
votes
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
vote
2answers
51 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
37 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 ...
0
votes
1answer
83 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 ...
4
votes
2answers
40 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 ...
0
votes
0answers
34 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 ...
0
votes
0answers
35 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-
1
vote
0answers
18 views

What is frequency response of vibrating string? [duplicate]

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 $Md_tx_2(t)+Cx_2(t)+Kx_1(t)=b(t)$. ...
1
vote
0answers
23 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
votes
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
votes
1answer
51 views
-1
votes
0answers
50 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 ...
1
vote
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, $$T_2=T_1(1+\frac12\alpha\Delta T)$$ ...
1
vote
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 ...
-1
votes
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
votes
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
votes
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)
0
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
votes
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
votes
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
vote
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
vote
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 ...
-6
votes
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
votes
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 ...
1
vote
0answers
54 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
vote
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 ...