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 questions.

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-1
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0answers
36 views

Show that any rotation can be represented by two successive reflections [on hold]

Show that any rotation can be represented by two successive reflections in two planes, both of which passing through the axis of rotation with the planner angle $\phi/2$ between them
0
votes
0answers
31 views

Will there be an induced emf in this situation?

Here is a (horrible) illustration: The first ring has a voltage $V_1$ applied to it through the voltage source on the left. Ring 1 has resistance $R_1$ whereas ring 2 has resistance $R_2$. Will ...
0
votes
0answers
18 views

Find the angle and force constituent [on hold]

See picture for the problem description. I know of one way to solve this problem: Use the law of cosines to obtain: $$ 500^2=F^2+750^2-2 \cdot 750 \cdot F \cdot \cos(30°) $$ Rearranging and ...
0
votes
1answer
23 views

Is it only possible when 600J of heat is exhausted and 400J of heat is converted into work? [on hold]

Is it only possible when 600J of heat is exhausted and 400J of heat is converted into work? Is the 600J heat will enter the cold reservoir and available to do work again? q1/T hot + q3 / T cold = 0 ...
1
vote
0answers
37 views

Potential due to a Uniform Ring [on hold]

Consider a uniform ring of mass $M$ and radius $a$ (?). I would like to prove that for $r > a$: $$\Phi(r) = \frac{GM}{r} \sum_0^\infty[P_n(0)]^2 \left(\frac{a}{r}\right)^n $$ Where $\Phi(r)$ is ...
0
votes
0answers
28 views

Problem in Solving an Equation in Quantum Mechanics [duplicate]

I am trying to reproduce this paper : http://www.ias.ac.in/pramana/v73/p573/fulltext.pdf But, somehow I am stuck at equation (7). The equation that I am trying to solve for particle outside the well ...
-3
votes
0answers
40 views

Conservation Laws and relativity [on hold]

A 50 kg meteorite moving at 1000 m/s strikes Earth. Assume the velocity is along the line joining Earth's center of mass and the meteor's center of mass. What is the gain in Earth's kinetic energy?
1
vote
1answer
57 views

Deriving photon propagator

In Peskin & Schroeder's book on page 297 in deriving the photon propagator the authors say that $$\left(-k^2g_{\mu\nu}+(1-\frac{1}{\xi})k_\mu k_\nu\right)D^{\nu\rho}_F(k)=i\delta^\rho_\mu ...
-1
votes
0answers
21 views

Commutator of $SU(2)$ angular momentum operators [on hold]

Prove the following statement. $$[J_i,J_j] = i\hbar\epsilon_{ijk}J_{k}$$ using rotation operators.
0
votes
1answer
68 views

What are great circles of 2-sphere?

What exactly are great circles, and how does one derive them? Given that the Lagrangian is: $$ L =\frac {1}{2}(\dot\theta^2 + \sin^2\theta\dot\phi^2)$$ it was written that the great circles were ...
0
votes
1answer
40 views

What is the equivalent resistance of this bridge circuit?

I am trying but could not find any way of calculating the equivalent resistance of this circuit. Please help me. Should I use the Wheatstone Bridge equivalent resistance, the Y-$\Delta$ transform, or ...
2
votes
1answer
33 views

Electrostatic Potential Energy Integral

I'm trying to calculate the total energy of a simple two charge system through the integral for electrostatic energy of a system given in Griffiths' book: $$U = \frac{\epsilon_0}{2}\int_V E^2 dV .$$ ...
0
votes
0answers
12 views

Deriving (spatial) angular momentum selection rule [on hold]

I am having a go at Problem 7.21 from Binney and Skinner's The Physics of Quantum Mechanics. Here's the first half of the problem: Here is my attempt at the moment: $$[ L^{2}, [L^{2}, x_{i}] = [ ...
0
votes
1answer
19 views

Motion and acceleration in a straight line [on hold]

A car with an initial velocity of 3 m/s has a velocity of 34 m/s after 3 sec. How far it moves in its third second of motion? acceleration V=U + at a = 10.3 m/s^2 x = ut + 1/2 a t^2 x = 3 (3) ...
1
vote
0answers
31 views

Where Does the Exponent Come From in the Expression for the Rotation Operator

I am currently reading John S. Townsend's "A Modern Approach to Quantum Mechanics." In section 2.2 he introduces the $\hat J$ operator, which he refers to as "the generator of rotations." He gives the ...
0
votes
0answers
39 views

Relativistic mass of lead at $.999999991c$? [on hold]

I've been doing a lot of reading on the LHC and the fundamental problems with breaching the speed of light. It's impossible because the amount of energy required would be, in essence, infinity+1. ...
1
vote
0answers
16 views

At time $t=0$, what are the magnitude and direction of the perpendicular component of dp/dt? [on hold]

In the dark in outer space, you observe a glowing ball of known mass 4.6 kg moving in the xy plane at constant speed in a circle of radius 7 m, with the center of the circle at the origin (< 0, 0, ...
1
vote
0answers
20 views

Estimate the distance covered [on hold]

I know it says estimate, but how? If it's linear I could do something, but it's a curve and so inaccurate. My best try was this. 1000 * 100 = 100000 Which gives me the area of the rectangle which ...
2
votes
2answers
46 views

Two-rotation coordinate transformation

I've designed an electronic device that uses a 3-axis accelerometer to measure the acceleration of an automobile. I'm only interested in accelerations in the plane of the road surface, so I want to ...
1
vote
1answer
66 views

Tangential acceleration [duplicate]

If you are spinning an object using a mass-less string with constant speed in a vertical circle, and when the object is at an angle with the vertical, what happens to the component of weight in the ...
1
vote
0answers
40 views

Tension problem for rotating object? [closed]

when an object (tied to a massless string) is moving in a vertical circle with constant speed, does it have tangential acceleration when it is at some angle (theta) from the vertical? I am assuming ...
1
vote
0answers
47 views

Showing the Hamiltonian of the $\alpha$ FPU is real

I am studying the $\alpha$ FPU chain which is a model of coupled oscillators with small non-linearity. For these systems, I derived the following Hamiltonian $H$ which is given by $$ H=\sum_{j=1}^{N} ...
1
vote
0answers
53 views

Geodesic equation from Euler - Lagrange

There are several ways to derive the geodesic equation. One of which is the variational method which I seemed to understand it because it was written in great details. Then it was mentioned that the ...
0
votes
1answer
57 views

Harmonic oscillator differential equation solution [on hold]

My math book explains how to solve second order equations like : $$\ddot{x} + \omega^2x = 0$$ but I end up with the general solution : $$A\cos(\omega t) + iB\sin(\omega t).$$ Now my physics book ...
1
vote
0answers
28 views

A particle is moving on a circular track with omega = 0.2926829268 rads/s. How many revolutions in 30s? [closed]

Physics HW Q: A particle is moving on a circular track with omega = 0.2926829268 rads/s. How many revolutions in 30s? What I have done: It seems to me that I must convert from rads/sec to ...
0
votes
0answers
14 views

Kinematics problem - three masses, two tensions, kinetic friction, and a pulley [closed]

I took a test in general physics yesterday that had the following kinematics problem: $\hskip 0.7in$ The 10kg body has downward acceleration $a=1.5\frac{m}{s^2}$ and there is a kinetic coefficient ...
-1
votes
0answers
19 views

side lifting lug load calculation [closed]

I have to find the load on A36 1/2" thick lifting lugs that are welded to a steel tank. The weight of the tank is 24,000lbs so each of the 4 side lugs need to support 6000lbs. I need to find the ...
2
votes
1answer
64 views

Doppler shift for a uniformly accelerating observer

This was given in textbook as an example. An observer on a spaceship with a four velocity $u$ is approaching from $x = +\infty$ a star at rest in the reference frame $S$ while undergoing constant ...
3
votes
1answer
45 views

Moments of vibrating string

I have to calculate first 10 moments for vibrating string with damping, but I don't know how to do it. I read about moments and in definition they mention linear system $$x'=Ax+Bu, \qquad y=Cx$$ with ...
0
votes
1answer
36 views

Spaceship Doppler frequency

A spaceship starts falling under gravity with an acceleration $g$ as measured by an observer Barry at rest on Earth. At the instant that the ship starts to fall, an astronaut Harry at the base of the ...
0
votes
0answers
30 views

Tension of two masses accelerating down an incline with friction? [closed]

I have tried multiple times, and I can't seem to understand how to solve this question. The question goes as follows: Two masses, M and m accelerate down an incline. They are connected by a massless ...
0
votes
0answers
17 views

Force between an electric charge and square? [closed]

An insulated square piece with total charge is Q, the side length is d. An electric charge placed on the axis of square and distance to square is d/2. (assume q*Q >0). calculate the force between the ...
0
votes
1answer
21 views

Finding electric field of a line charge [closed]

I have a bit of an issue setting up the integral for finding an electric field of a particular scenario. The scenario is that a line charge of length R is a distance R from the left side of the ...
-2
votes
0answers
27 views

2-D Motion Question which is very confusing [closed]

I am working on the below problem. I am getting the answer as 31.70 meters but it is not right. A stunt man drives a car at a speed of 20 m/s off a 29-m-high cliff. The road leading to the cliff ...
0
votes
0answers
10 views

If statements in equations? [migrated]

When creating an equation is there any way to let someone know that if this number doesn't fit into this then use this other equation? Ex: X>1 then use x+y if X<1 then use x-y. Or do you just have ...
0
votes
0answers
20 views

Under-damped oscillator - how to determine speed?

At t=0 a mass M is stretched from equilibrium by x with spring constant k and damping coefficient $\gamma$. How do I determine how fast a weight is moving when it passes through equilibrium on an ...
-4
votes
0answers
20 views

How do I calculate the angle made by this falling rod? [closed]

A uniform rod of length 1 is in contact with a smooth vertical wall and a smooth horizontal floor. Initially, the rod is kept almost vertical. Now the rod is released. Find the angle made by the rod ...
4
votes
3answers
76 views

Motion on a frictionless vertical sinusoidal track

Today during lesson, my mechanics teacher provided a diagram of a "bowl" of the following shape: The top left and the top right have the same height, and the top right part is horizontal. He ...
-1
votes
1answer
15 views

What is the objects speed? [closed]

A magnetic field will deflect a charged particle perpendicular to its direction of motion. An electron experiences a radial acceleration of 8.60E+14 m/s^2 in one such field. What is its speed ...
1
vote
0answers
28 views

Parallel transport of a vector on a curve on a sphere [closed]

I want to do a calculation of a parallel transport along a curve on a sphere, but I think I'm lacking a bit the basics of using different coordinate systems and curves there because I never did much ...
0
votes
1answer
23 views

Maximum Velocity of Coupled Oscillators with Different Masses

Question: Two different masses $M_1$ and $M_2$ such that $M_1 > M_2$ are attached by a spring with spring constant $k$, which is stretched by some initial displacement $\Delta$ x from equilibrium. ...
3
votes
1answer
93 views

Force exerted by light on a moving mirror

Consider a light with energy density E shining uniformly over a mirror. The mirror has an area A. The mirror is moving at with a velocity β. Calculate the force that the photons exert on the ...
2
votes
1answer
184 views

Evaluate $\langle \mathbf{p} | 1/\hat{r} | \mathbf{p}' \rangle$

In Sakurai's Problem 1.27 b), we use $\langle \mathbf{r} | \mathbf{p}\rangle = e^{i\mathbf{p}\cdot\mathbf{r}/\hbar}$ to show that $$ \langle \mathbf{p} | F(\hat{r}) | \mathbf{p}' \rangle = ...
1
vote
3answers
46 views

Is there a place on the equipotential surface where a charge feels no electric force? [closed]

I'm given a graph of an equipotential surface where I need to find a place where a charge feels no electric force. I feel like it will be where the voltage is zero, which would be 2G on the graph, ...
3
votes
0answers
110 views

How is the method of Lagrange multipliers used for multiple constraints of multiple variables? [closed]

Let's say for example that I have two constraints $f(x,\dot{x},y,\dot{y})$ and $g(x,\dot{x},y,\dot{y})$ and a Lagrangian $L(x,\dot{x},y,\dot{y})$. What are the Euler-Lagrange equations of the first ...
1
vote
0answers
12 views

If a nozzle that converges from an inside diameter of 5cm to 3.5cm carries a gas at a VFR of 0.10 m^3/s, what is the change in average velocity? [closed]

If a circular nozzle that converges from an inside diameter of 5 cm to 3.5 cm carries a gas at a volume flow rate of $0.10 m^3/s$, what is the change in average velocity of the gas? (A nozzle being a ...
1
vote
0answers
26 views

2D Kinematics cliff problem [closed]

I'm having trouble with a kinematics problem... "A potato gun is fired up at a 50 degree angle off a 35 meter cliff. If it landed 7.5 seconds later, how far away from the base of the cliff ...
1
vote
0answers
53 views

Energy of RLC circuit

If you are given a general differential equation for an RLC circuit, for example, $$L\left(\frac{d^2 Q}{dt^2}\right) + R\left(\frac{dQ}{dt}\right) + \frac QC = V\cos(\omega t),$$ which is a driven ...
0
votes
1answer
25 views

Binary Mass Function Plot

Suppose that we have a circular eclipsing binary system with orbital period of $P = 2 \text{days}$, and with one star with a radial velocity of $v_{1r} = 100 km/s$. The other star is to dim for its ...
4
votes
1answer
78 views

Evolution of harmonic oscillator in path integral formulation

The unnormalized ground state of the harmonic oscillator (choosing units such that $m = \hbar = \omega = 1)$ is $$\tag{1}\psi(q,t) = \exp(-q^2/2-it/2).$$ The transition function is ...