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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13 views

Efficiently compute the bases functions of the Signal

Let there be 4 1D signals such that \begin{cases} x(t)=4\sin(10\pi t) \\ y(t)=8\cos(20\pi t) \\ z(t)=16\sin(30\pi t) \\ m(t)=x(t) +y(t)-z(t) \end{cases} Is there a way to compute ...
0
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1answer
24 views

String theory $bc$ system CFT

$bc$ CFT is an example of free-field CFTs. action is $$S = \frac{1}{2\pi} \int d^2 z b \bar{\partial} c$$ How can we obtain equation of motion? Polchinski-volume 1-page 50 writes that ...
0
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0answers
11 views

Scalar Green's function of wave equation in a multilayer medium

A point source is located somewhere $\mathbf{r}_0$ in planar stratified media that consists of $n-1 $ layers (or $n$ types of materials). The physics is governed by the scalar wave equation ...
-6
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0answers
32 views

Calculating the change in entropy [on hold]

What is the magnitude of the entropy change of $2~\text{kg}$ of water heated from $20^{◦} ~\text{C} \to 40^{◦} ~\text{C}$? Assume the heat capacity of water is $4186~\frac{\text{ ...
1
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0answers
22 views

Chemical Potential at Triple Point

How does one calculate the chemical potential/Gibbs Free energy at the triple point of a substance given only the temperature and pressure of the triple point, and the volume of each phase? I cannot ...
-3
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1answer
19 views

Induction Oscillation [on hold]

A bar (m=100g, l=10cm) is moving in a constant magnetic field $B$ as shown above. The resistor $R$ is $1\Omega$. The bar is attached to a spring with spring constant $10N/m$, can you derive ...
-2
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0answers
22 views

Why is the rotation not zero and the divergence zero in the figures below? [migrated]

Why is the rotation not zero and the divergence zero in figure 1 and figure 2 below? Figure 1 Figure 2
0
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0answers
58 views

Interesting approach to Kepler problem

I won't go into the explanation of this idea, because it is explained in this blog post. In this paper, which was featured on John Baez's blog, $\frac {dt}{d\lambda}$ is given as $\frac r V$, where ...
2
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1answer
68 views

Weightless person in a cart on a rail [on hold]

In a problem I'm trying to solve I'm having a conflict between my understanding and the proposed solution of the problem. In the problem, a cart of mass $m$ is put at rest in the start of a ...
0
votes
0answers
9 views

Geophysics: Dynamic form factor and Equipotential surfaces [on hold]

I've got the following problem which I need help with. I'm used to calculating coefficients when the problem is about ellipsoids and first order approximations. But when it comes to spheres and ...
0
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0answers
13 views

Propagation of incertitude - specific example [duplicate]

I am setting up an experiment, where I know the force and the incertitude (delta) of that force. However, I need to graph the logarithm of that force with the incertitude of the log. Can someone help ...
1
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1answer
17 views

Moment of Inertia Calculation [on hold]

A uniform disc has centre O, radius a and mass 2m. It is free to rotate in a vertical plane about a horizontal axis through O. A particle P of mass m is placed on the highest point of the rough edge ...
3
votes
1answer
15 views

Determining straining force and reaction forces on a beam

A homogenous beam $OA$ with the length $4a$ and the mass $m$ can rotate in the vertical plane along a horizontal axis through $O$ and is kept in equilibrium by a wire running from the points A and C ...
1
vote
1answer
21 views

How to derive velocity pressure in English units?

I know that velocity pressure can be calculated from dynamic pressure according to the potential energy of pressure (from Bernoulli's equation): $$ P = \frac{1}{2} \rho \overline{V}^2 $$ where P = ...
-1
votes
0answers
12 views

How do you calculate the angular momentum of a dumbbell after a collision? [on hold]

In outer space, far from other objects, a small block of mass $m$ traveling at speed $v_1$ approaches an object initially at rest that consists of two small spheres each of mass $M$ connected by a ...
1
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0answers
49 views

Are neutrinos weekly interacting particles? [on hold]

Occasionally, I read about weekly interacting neutrinos, and although I know this is a typo, I wonder if it happens to be true. Do average neutrinos, as they fly through the universe, really interact ...
-5
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0answers
20 views

Net force acting on the block along the inclined path can be mgcos(theta)? [on hold]

If we take the angled marked with red curve then the net force along the x axis or inclined path comes out mgcos(theta) is is correct?
0
votes
1answer
44 views

Is there a spacelike curve connection two events in Minkowski space?

Assume two events in Minkowski Space (signature $(-,+,+,+)$) $p_1$ and $p_2$. One claims that there is a spacelike curve which connects these two points in Minkowski space. I have some trouble to ...
1
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2answers
89 views

Dropping a weight onto a spring scale

Say I drop a 5kg weight from a height of 1 meters onto a spring scale like many people have in their bathrooms. On impact the scale will show a higher weight than 5kg. Question: Which quantities ...
-7
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0answers
33 views

HOMEWORK HELP! Simultaneous equations (graphical method) [on hold]

I just spent like half an hour on this and i am really not getting it. Any suggestions? A man buys 3 Ipods and 2 vouchers for £280 A woman buys 1 Ipod and 4 vouchers for £260 Form 2 equations from ...
0
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0answers
21 views

Computation of the partition function of a fermionic oscillator

I don't understand the following steps in the calculation of the partition function for a fermionic oscillator (Nakahara). The eigenvalues of the operator ...
0
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0answers
22 views

Continuum mechanics treatment of the Lariat Chain [on hold]

Would anyone be willing to help me with a homework problem I'm doing? I've been working on the assignment all weekend and this one problem just will not click. I already have satisfactory solutions to ...
-1
votes
0answers
22 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
-2
votes
1answer
23 views

Finding gravitational acceleration question [on hold]

I was working on an assignment and one of the questions is as follows: Find the value of g (the gravitational acceleration) on top of mountain $7.61~\text{km}$ above sea level. Assume that the ...
0
votes
1answer
24 views

Disparity between two texts on intensity and phase interference - which is right?

So, I'm learning phase interference. Imagine we have two waves. $$ E_1 = A_0sin(wt) $$ and $$ E_2 = A_0sin(wt+\phi) $$ With $$ \phi = \frac{2\pi}{\lambda}dsin(\theta) $$ Which is the path ...
0
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1answer
25 views

Angular velocity in central force field

For motion in a central force field consider a rotating reference frame, which is characterized by the Euler angles $\alpha$, $\beta$, $\gamma$ associated with the rotation of the frame of Cartesian ...
1
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0answers
27 views

How to add together non-parallel rapidities?

How to add together non-parallel rapidities? The Lorentz transformation is essentially a hyperbolic rotation, which rotation can be described by a hyperbolic angle, which is called the rapidity. I ...
0
votes
1answer
48 views

How to calculate angular velocity given constant tangential acceleration? [on hold]

A car starts moving in a circle with a radius of $200 \text{ m}$. It has a constant tangential acceleration of $1{\text{m}\over {\text{s}}^{2}}$. a. What is the angular acceleration? b. What is the ...
2
votes
3answers
94 views

Distance traveled by a water jet

I helped my kid in a science fair project, where we punctured holes in a water bottle at various heights and then measured the distance traveled by the water jets before they hit the ground. The ...
0
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0answers
30 views

Free body driagram of box and plate with a friction force on a smooth surface

On a smooth surface we have a plate of 40 kg and on that plate a a box of 10 kg. Between the plate and the box there is a ...
0
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0answers
35 views

How important is doing exercises in learning physics? [on hold]

I am a Chinese student who is currently studying physics at Nanjing university. And I just entered university a year ago. I am quite curious to know how you guys learn physics when you are in ...
0
votes
1answer
27 views

Determine normal forces on tilted table [on hold]

A table with the mass m, the height a and the width b is resting on a tilted floor with the angle of rake $\alpha$. A block at A prevents the table from sliding. Determine the normal forces from the ...
1
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0answers
22 views

Gamma matrices in Decay Calculations [on hold]

I am trying to calculate the transition amplitude, $\lvert M^2\rvert$, for the process where a top quark (momentum p) decays to a bottom quark (momentum q) and a $W^+$ boson (momentum k). I am ...
0
votes
0answers
18 views

The angle of incidence of prism if emergent angle is 90°. Answer in terms of angle of prism and refractive index of prism [on hold]

A ray of light is incident at an angle of incidence i on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is n, ...
0
votes
3answers
26 views

Path followed by a free test charge in an electric field region represent the electric lines of forces?

As we know that if we put any free test charge in an electric field which is moving horizontally then it will experience an repulsive force and move in that direction so by that we can say that for ...
2
votes
2answers
151 views

Why do electric field lines start and end at 90 degree at the surface of a conductor? [duplicate]

There is one property of electric lines of forces which states that: Electric field lines start and end at 90 degree at the surface of the conductor. But why is that so? Is there any proof for ...
2
votes
2answers
42 views

Work done by frictional force on a sliding block

A block slides across a table horizontally with an initial velocity $V$. The frictional force $F$ brings it to rest after its Centre of Mass covers distance $S$. What is the work done by the ...
0
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0answers
25 views

RC Circuit Analysis

I want to correct three misunderstandings about the following RC circuit. 1) How does current move directly after switch S gets closed? Current runs through all three circuit components to begin ...
-2
votes
0answers
16 views

Find magnitude of the net magnetic field at points A, B, and C between two parallel wires [on hold]

I've been having a lot of problems with this problem. Been working on it for over to an hour and nothing. I've been using amphere's law but I think I'm getting r wrong, here's one of my most recent ...
0
votes
0answers
22 views

Help with inclined slope motion? [on hold]

I have this question (5ii) and I was wondering why this wouldn't work, why can't I solve for acceleration using $v^{2}-u^{2}/2s$=$a$ then solve for $t$? I obviously have to resolve and use $p=fv$ but ...
1
vote
2answers
39 views

Electric field due to a finite line charge [on hold]

I was wondering what would happen if we were to calculate electric field due to a finite line charge. Most books have this for an infinite line charge. In the given figure if I remove the portion of ...
1
vote
1answer
78 views

When will the pringles can fall?

When I'm pushing a tall, cylindrical object stood on its end (like a Pringles can) I can push it near its bottom, and it will slide forwards, or push it near the top, and it will topple over. So, ...
2
votes
0answers
28 views

Current carrying conductor with a loop at a distance [on hold]

In Fig, there are an infinitely long conductive wire and a circle conductive loop C with the radius r and the number of turns n. The distance L between the wire and the loop is much larger than r, ...
0
votes
0answers
15 views

water pressure relationship to volume [on hold]

I have a one inch pipe 120 feet long and caped. I have a 60 pound input of pressure. I put a half inch pipe at the end and open it. What happens to the pressure in the one inch pipe? If I add another ...
1
vote
1answer
37 views

About shift operators

The question is this: Does $$L_+ L_- Y_{lm} $$ ,where $Y_{lm}$ is a spherical harmonic function, equals to zero. If so, why? The two operators above are defined as $$L_+ ={L_x + iL_y } $$ $$L_-={L_x ...
3
votes
1answer
35 views

Average force for repeated elastic collisions

I was asked to compute the average force exerted by a rigid spherical ball (mass $m$) on the floor over time $t \rightarrow \infty$, in a situation where the ball is dropped vertically from a height ...
2
votes
0answers
23 views

Distribution forces

I've got two trees and between them is a rope. When someone about 100kg sits at the center of the rope, what are the forces on both parts of rope (to the left-hand side from the person and right-hand ...
1
vote
1answer
49 views

Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [duplicate]

I want to know the configuration where the system would be most stable.I only know basic Physics & Maths and cannot start solving the problem.I can understand it for 4 charges and 6 charges as a ...
0
votes
0answers
24 views

Charged particle inside a hole in a charged layer

The layer $-a\le x \le a$ is homogeneously charged with a electric charge density $\rho \gt 0$ and on the x-axis a thin hole is made. A particle with mass $m$ and charge $q \gt 0$ move on the ...
0
votes
0answers
47 views

Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [on hold]

I want to know the configuration where the system would be most stable. But I cannot think of a way to start solving the problem. I've solved it for 4 charges and 6 charges and they have a symmetric ...