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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3 views

How to design this material? (in theory)

My university task is to design an injectable biomaterial that fills a tissue void and doesn't diffuse away from the site of an injection. I need to describe how I would carry out this design in ...
-3
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0answers
7 views

Total Energy Stored in Seven Capacitors

The capacitive network shown in the figure is assembled with initially uncharged capacitors. A potential difference, Vab = +100V, is applied across the network. The switch S in the network is kept ...
0
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0answers
8 views

Calculating values related to angular momentum and then their uncertainties

Here is the problem: And here is my work (sorry it is handwritten, it would take a while to type this out) My problem is that I'm not sure if it's right or if it makes sense to keep getting 0 ...
1
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1answer
19 views

Finding the appropriate coordinate transformation given two metrics

Given the two-dimensional metric $$ds^2=-r^2dt^2+dr^2$$ How can I find a coordinate transformation such that this metric reduces to the two-dimensional Minkowski metric? I know that ...
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2answers
32 views

Proving the Lorentz invariance of the Lorentz invariant phase space element

I have been looking around for a satisfactory answer to prove that $$\frac{d^3\vec{p}}{2E_{\vec{p}}}$$ where $E_{\vec{p}}=+\sqrt{(|\vec{p}|c)^2+(mc^2)^2}$, is Lorentz invariant. The standard answer ...
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1answer
14 views

A 45.0 kg girl is standing on a 163 kg plank?

The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. The girl begins to walk along the plank at a constant velocity of 1.47 m/s relative to the ...
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2answers
74 views

Confused about Gauss's Law for parallel plates

I am having trouble understanding Gauss's Law. Suppose we wish to find the electric field strength between two parallel plates with charge density $\sigma$. I know it should be ...
0
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1answer
17 views

Squaring the matrix element and summing over the spins of outgoing particles?

I found the matrix element in a scalar interaction $\nu_ee \rightarrow \nu_ee$ to be $$M=\bar{u}(\nu,q_2)u(e,p_1)\bar{u}(e,p_2)(1-\gamma_5)u(\nu,q_1)$$ But I do not know how to find the $|M|^2$ and ...
1
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0answers
25 views

How to solve a difficult equation describing large vacuum fluctuations?

Suppose that a Quantum System can be described by the wavefunction $\psi(\vec{x},t)$, but due to the occurence of chaotic noise within the Quantum System, only the "filtered" wavefunction ...
0
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0answers
28 views

Finding the Expectation Value of basis states

I am a Mathematician and I am taking a Quantum Computing class. We have been asked to find the expectation value of $X$ tensor $Z$ and $H$ tensor $H$. X is the not operator and switches the state the ...
0
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1answer
40 views

Difference of potential between points [on hold]

I have the following question: What is the potential difference between point A - B? Could somebody please explain me how should I count it? The voltage U=18V. I found out that V1=8V, V2=10V, ...
1
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0answers
17 views

Laser travelling through a radially graded index of refraction

A laser beam propagates through a region whose refractive index varies as $\mu=\mu_0(\frac{r}{r_0})$. At a distance of R the beam makes an angle of 30° with the normal. Find the minimum seperation ...
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1answer
34 views

Peskin “An Introduction to quantum field theory”, problem 4.1

I'm trying to solve problem 4.1)c) in Peskin's book "An Introduction to quantum field theory" using this answer sheet. I don't understand why lambda correspond to a line in Feynman diagrams. Any idea? ...
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2answers
40 views

Calculating the electric field of an infinite flat 2D sheet of charge

I was trying to calculate the electric field of an infinite flat sheet of charge. I considered the sheet to be the plane $z=0$ and the position where the electric field is calculated to be ...
0
votes
2answers
62 views

Can we define the zero potential at an imaginary point?

Consider a force field defined as $$\vec{F}(x) = \left(\frac{A}{x^2}-B\right)\hat{i}\space$$ where $A, B$ are positive constants. We want to get the potential energy function for this field. We can ...
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0answers
42 views

Quantum mechanical expectation of angular momentum along different axes [on hold]

This is a question from Concepts of Quantum Mechanics by Mathur & Singh, and I don't know where I should start from: Show that, for a state $|j,m \rangle$, corresponding to a definite value of ...
-7
votes
1answer
41 views

vectors, space and coordinate systems, [on hold]

An object moves from the position $r_1 = (1,3,-5)$ to the position $r_2 = (-1,4,8)$ during the time $8~\text{s}$. Find displacement, distance, average velocity, average speed.
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1answer
57 views

Integral calculation [on hold]

I do some calculation in QED, but I can not calculate such integral $$ I(a_1,a_2,m_1,m_2)=\int\frac{ d^2\mathbf{x} d^2\mathbf{y}}{(1+\mathbf{x}^2)(1+\mathbf{y}^2)((\mathbf{x}+a_1 ...
0
votes
1answer
69 views

How does one normalize this wavefunction? [on hold]

Here is the question: So I could write $ N = \dfrac{1}{{\sqrt{<Ψ|Ψ>}}} $, right? Considering the parentheses in the exponential term, it looks like a good idea to switch to spherical polar ...
0
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2answers
29 views

Using a charged capacitor to charge two others

Here is the homework question in question: The figure (below) displays a 13.1 V battery and three uncharged capacitors of capacitances C1 = 4.08 μF,C2 = 6.19 μF and C3 = 3.30 μF. The switch is thrown ...
2
votes
1answer
58 views

$SU(3)$ irreducible representations with tensor method

I am dealing with the tensor product representation of $SU(3)$ and I have some problems in understanding some decomposition. 1) Let's find the irreducible representation of $3\otimes\bar{3}$ we have ...
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2answers
49 views

Would it be possible to make a space elevator only in the atmosphere?

I wonder if with current day technology we could make a "floating platform" which hangs from a satellite by a space elevator. This could allow a "launch process" involving floating a balloon to the ...
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1answer
38 views

How do you accelerate atoms/particles?

So I'm in 11th grade, and I'm writing a theory for my Physics professor and I need help. I need to know how you can make atoms/particles travel faster. For example, making sound travel a little bit ...
0
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2answers
58 views

Balancing a pencil

I came across this equation for balancing a pencil while solving some problems: $$ml\ddot { \theta } =mg\theta $$ Where $l=$the length of the pencil, and $\theta$ is the angle it makes with vertical. ...
2
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0answers
19 views

Homogeneous turbulence [on hold]

I'm trying to demonstrate the Karman-Howarth expression of isotropic turbulence for the velocity correlation functions: $R_{ij}(r)=A(r)_{ij} + B(r)\delta_{ij}$ since: \begin{align} A(r) r^2 + ...
0
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1answer
26 views

kinematics: parabolic movement [on hold]

How does the formula $ax^2$ is affected by the angle and the power of the launch of, let's say, a cannon ball, (regardless of its mass)? I am trying to create a simulation, and everything I have to ...
0
votes
1answer
10 views

Energy under constant pressure and temp

Conceptual problem: let A + 2B -> C + 2D be a reaction under constant pressure P and temp T, that goes all the way towards the products. A,B,C,D are ideal gases. let $\Delta H$ be the molar enthalpy ...
-1
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0answers
17 views

Resistance in Potentiometer [on hold]

A potentiometer is shown in the figure. a) How will the balancing length be affected if resistance (R) is increased or decreased ? b) Will the balancing length be affected if resistance (S) is ...
1
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1answer
21 views

How do you show that the normal derivative of the magnetic vector potential is discontinous across a surface current?

This is from Griffith's "Introduction to Electrodynamics" 4th edition, problem 5.33. I need to show that $$ \tag 1 \frac{\partial \textbf{A}_{above}}{\partial n}-\frac{\partial ...
-4
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1answer
25 views

How I can solve this ? (kirchhoff's law) Plz discuss it to me [on hold]

the remaining of question is ( careful choice of suitable loop can make it easier ? i choose outer loop and answer it like that: 10 Volt = ( I X 10 ohm ) + ( I X 10 ohm) but it give wrong answer ...
0
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0answers
10 views

Transistor as Oscillator [migrated]

While I was studying the use of Transistor as an Oscillator from my Fundamentals Of Physics By Halliday, Resnick and Walker , I faced several confusions. My book says that when the switch S1 is ...
-1
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2answers
25 views

How do we prove that the initial velocity is equal to final velocity relative to centre of mass?

In elastic collision it is stated that the initial velocity relative to centre of mass is equivalent to final velocity of centre of mass of the same object. How do we prove that?
0
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2answers
51 views

With what initial speed does the person leave the ground to reach a height of 60 cm? [on hold]

An average person can reach a maximum height of about 60 cm when jumping straight up from a crouched position. During the jump itself, the person's body from the knees up typically rises a distance of ...
0
votes
1answer
23 views

Probability density function of a particle for computation [on hold]

I'm writing a program, part of which relies on a particle being able to change location similar to a how a real particle would behave (pardon my physics). For example, on a grid of 100x100, a ...
-5
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0answers
46 views

Ok ok this is a homework problem, but I'm having trouble with it [on hold]

Where do I even start. I've converted the miles that I should be getting in total and arrived at 700 miles total. From here, any hints on what I have to do?
0
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1answer
46 views

Question about angular momentum operator

To show that the eigenvalue to $L^2$ is proportional to $\hbar^2$ is shown from $L_z=xP_y-yP_x$ $p_y=-i\hbar\frac{\partial}{\partial y}$ $p_x=-i\hbar\frac{\partial}{\partial x}$ ...
3
votes
0answers
45 views

How much work can a single grain of rice do? [on hold]

I found a website saying a grain of rice contains 1/10 kcal. I'm not a physicist and haven't done maths for a long time. But here's what I came up with: E = m * g * h One small calorie equals ...
3
votes
1answer
41 views

The ADM Energy of Gravitational Waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of Gravitational Waves.And they said the result ...
-1
votes
0answers
50 views

Why do motors have a speed limit? [duplicate]

The force which will move a body with this motor will be the difference between the force of the motor say 2N and the resistance - friction force - say 1N then the sum of forces will always be ...
-3
votes
0answers
26 views

Rocket needs to make course correction what mass of gass must be expelled [on hold]

A(n) 5200 kg rocket traveling at 3900 m/s is moving freely through space on a journey to the moon. The ground controllers find that the rocket has drifted off course and that it must change direction ...
-1
votes
0answers
13 views

How can I calculate wavelength in the following problem? [on hold]

Ultrasonic sound of frequency 100 KHz emitted by a bat is incident on a water surface. What is the wave length of reflected and transmitted sound? (Given that speed of sound in air is 340 m/s and in ...
-1
votes
0answers
38 views

Capacitor question [on hold]

Assume a 1200F ultracapacitor is initially charged to 12V by a battery and is then disconnected from the battery. If charge is then drawn off the plates of this capacitor at a rate of 1.0mC/s, how ...
2
votes
3answers
68 views

How can Denver offer Hot Air Balloon rides?

So the air density in Denver is 1.0 kg/m^3. And heated air has the density of 0.95 kg/m^3. So adding the weight of the basket and balloon I don't understand how a hot air balloon could get off the ...
1
vote
2answers
32 views

Working out velocity (including air resistance) [duplicate]

For my computing project, I am creating a projectile simulator but I cant seem to get my head round the air resistance. I tried by working out the horizontal and vertical velocity by solving it ...
0
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0answers
22 views

How to calculate explicitly the *external leg correction* diagram

I tried to calculate the Amplitude of the external leg correction of figure 6.1 in Peskin&Schroeder. I focus on the diagram with one incomming charged fermion $f^-$ (with momentum $p'$), then a ...
-1
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0answers
61 views

What does basis function actually mean?

I want to know that how any signal can be represented as sum of basis vector and what basis function actually means? Can anybody explain with simple examples?
0
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2answers
49 views

How does the object at constant speed pass the accelerating object?

A car starts from rest and move with constant acceleration of $4\frac{m}{s^2}$ and at the same time a motorcyclist moving with a constant speed of $36\frac{km}{hr}$ overtakes and passes the car. ...
0
votes
0answers
34 views

Thermodynamics - Efficiency of an engine [on hold]

I am taking a mathematical physics course and got stuck on this rather simple problem Consider a thermodynamic cycle of monoatomic gas () I want to calculate efficiency of this cycle I know that ...
-4
votes
0answers
26 views

assume that air resistance is proportional to speed [on hold]

Assume that air resistance is proportional to speed. A particle is thrown directly downwards with initial speed equal twice it's terminal velocity. Obtain a fomula for the time it takes for its speed ...
0
votes
1answer
25 views

Derivation for certain non uniformly accelerated movements [on hold]

A sphere of $m_1$ is thrown at a speed of $v_i$ perpendicular to the surface from the surface into the atmosphere.. Are there equations for position $x(t)$ and the speed $ v(t) $ of the sphere at a ...