Confused Definition and 1000 Threads

Hello! I have a classical Lagrangian of the form $$L=A\dot{x_1}^2+B\dot{x_2}^2+C\dot{x_1}\dot{x_2}cos(x_1-x_2)- V$$ the potential is irrelevant for the question and A, B and C are constants. When doing $$\frac{d}{dt}\frac{\partial L}{\partial \dot{x_1}}$$ the solution gives this...

Hey everyone! In a dilemma again, oops. I'm in the physics and astronomy program in university - going into my second year. I've completed courses for Astronomy and Physics in first year (same courses except astronomy has an extra - astronomy- course). Now that I'm selecting courses for second...

Hi, I'm an instructor at an online school, and my text says “ Air pressure is the amount of pressure the atmosphere places on the surface of Earth. Air pressure is usually measured as the weight of the column of air above a square meter (N/m2). As altitude increases, air density decreases and...

Hey, so here is my equation: 4x+6=-10 I'm not sure how to figure this one out, I'm confused by the -10 part.

Homework Statement Homework EquationsThe Attempt at a Solution Are we calculating the water that is falling when it is outside of the pipe. Not within the pipe? I just want to clarify. Because if i assume that the function of the speed is out of the pipe, then i get a correct answer...

Hello, I'm reviewing kinematics for an upcoming AP physics exam, but I seem to have forgotten a crucial fact. In typical rocket problems (when the rocket blasts off with an initial acceleration for example 5 m/s^2), why don't we subtract 9.8 from 5m/s^2 when using a value for acceleration? When...

The main topic I'm struggling with is as follows: Strain, stresses and constitutive law in a 1D,2D, and 3D linear elastic model i. Kinematics:displacements and strains (something about stress, strain and displacements fields is also mentioned) ii. Stresses and equilibrium iii.Constitutive law...

I was thinking about hall conductivity, when this question popped up. If there is a magnetic field and an electric field perpendicular to it, then a hall current is generated since the ions have larger gyro radii compared to electrons. Now this current would produce a J cross B force in the...

Why do we not need to consider direction when determining the change in potential energy? Why do we need to consider it in case of force? Or am I interpreting the question correctly?

Homework Statement The problem states: Determine the voltage labeled v in the following circuit: https://ibb.co/hz0Q37 The variable is the voltage across the 2 ohm resistor. The ground I chose for this example is located in the center of the circuit. Homework Equations V=IR I guess. The...

Homework Statement Find and prove ##\operatorname{lim} \frac {1}{n^2}##. Homework Equations In the textbook, we assume that the limit is going to infinity without writing it. If L is the limit, we have for all ##\epsilon > 0##, there exists ##N## such that ##n \epsilon \mathbb{Z}## and ##n >...

I am looking at the generators of the Lorentz group. The literature commonly refers to the generators as Mij, Ji and Ki and defines: Ji = (1/2)∈ijkMjk I am confused about the factor of (1/2) in this equation as I thought that Mij is essentially the same as Ji This also shows up in Λ=...

I am trying to use Weighted Least Squares with a linear model: Y = Xβ + ε, where Y are some observed measurements and β is a vector of estimates. For example, in this case β has two terms: intercept and slope. The weighted least squares solution, as shown here, involves a weight matrix, W...

I am completely baffled by bit of notation in Quantum Mechanics Concepts and Applications by Zitteli. He is trying to get the differential equation for the ground state of a harmonic oscillator using the algebraic method as opposed to Schrodinger's equation. I suspect he is compressing a lot of...

Homework Statement Use the diffence method to sum the series ##\sum_{n=2}^N\frac {2n-1}{2n^2(n-1)^2}## Homework Equations from the textbook by Riley i have ##S_N=\sum_{k=1}^m f(N-k+1)-\sum_{k=1}^m f(1-k)## The Attempt at a Solution I prefer to write it as ##S_N=\sum_{k=1}^m...

Homework Statement Using the E-L equations to get the EoM from the action. Homework Equations I am using E-L equations in the form: ## \frac{\partial}{\partial_u} \frac{\partial L}{\partial_u \phi}-\frac{\partial L}{\partial \phi} ## where ##L ## is the Lagrangian The Attempt at a...

Homework Statement Calculate energy of electron in first excited state of hydrogen atom. Homework Equations n=2 when i use E=-13.6 (z/n)^2 and then use E=hc/lamda(wavelength) then wavelength is coming wrong The Attempt at a Solution the correct answer is 6.68 armstrong.

I was reading a book on black holes by Kip Thorne the other day, well weeks really, and I came across this in one of the footnotes 10^10^79 (10 to the power of 10 to the power of 79) And I really don't know what it means. Does it just mean what it says? If it does can you raise a power to a power?

Homework Statement A sled is pulled across the barren winter landscape at an angle of 26.0° from the ground with a force of 74 N. If the sled is pulled over a distance of 27 m, how much work was done on the sled? Round your answer to two decimals Homework Equations W = f x s x Cos The...

Homework Statement Homework EquationsThe Attempt at a Solution Hi! I got the magnitude using F=qvB using information from the top of the qs. But the direction is confusing me. I used the Fleming's left hand rule but it sort of isn't giving me the right answer

So, while textbook was deriving Liouville eq, this is one of step the book uses. I don't understand this step at all. Why is this step true?

Homework Statement acceleratin as function of time ##a(t)= 2t+1## we know that v(0)=0 and s(0)=0 find v(t) find v(5) find s(t) find s(3) and I was thinking about also what happens when t is negative number, is it possible to find also v(-2)? what about s(-3)? Homework Equations integration...

I have read section from "Kleppner and Kolenkow, An Introduction to Mechanics" about Newton's 3rd law of motion, What does red-lined sentence means ? Why "somewhere in the universe ... on some other body" ? Please explain.

Homework Statement Imagine a ball on a string that we swing vertically so that the hight changes. By conservation of energy the velocity of the ball must change right? Because at the highest point of the swing it will have maximum GPE but at the bottom, minimum right? Watching many videos has...

Hello! I'm just having trouble understanding the logic about tension in strings. m = 5[kg] v = 2.8 [m/s] g = 10 [m/(s^2)] String in massless and air friction is negligible The question is what the tension in the string is when the ball is in the bottom position. My reasoning is that the...

Homework Statement A.[/B] Suppose I have a block of mass 'M' that is attached to a wall via spring of coefficient 'k' , the spring has rest length Xo . Suppose I look at the problem at some time 't' such that the spring is being compressed and the block moves left ( moving towards x = 0 ) ...

Hi everybody, Consider the situation illustrated in the attached figure . A large water tank at elevation z1 is connected to a penstock with diameter D and outlet at elevation z2. The flow in the penstock is Q. The outlet of the pipe is connected to a valve and nozzle that direct a jet of water...

Hi. I'm self-studying particle physics.Just been looking at some questions where a reaction is listed and the questions asks to draw a Feynman diagram for the reaction and state which force is involved. I have the answers but they all seem so random and I would like to know how to decide which...

Homework Statement A skier (m=59.0 kg) starts sliding down from the top of a ski jump with negligible friction and takes off horizontally. If h = 6.60 m and D = 10.6 m, find H. Homework EquationsThe Attempt at a Solution The solution was provided, this is a sample problem. I'm just very...

I have no clue how to use it. Can someone tell me in a basic way? Also provide links for downloading? Note, I haven't even downloaded it. I recently downloaded MikeTex but have no idea how to start this all out. I need this for writing a research paper.

I'm currently at war with myself. I'm pursuing chemical engineering as of now, mainly because of two reasons. The two reasons consisting of me wanting too have some knowledge in mathematics, physics, and chemistry. The other of course is money. Money because of me needing too support my family...

Homework Statement For an engineering assessment (first year with no electrical background), we are using a solar panel to power an element for a distillation system. we have calculated our heat energy output requirement that we need from our heating element as being 800 J/s. For simplicity we...

Homework Statement Calculate the energy needed for 1 kg mass at the velocity of 2 m/s go up to the velocity of 6 m/s. Homework Equations Ek = mv2/2 The Attempt at a Solution From the mass point of view, it is stationary and goes up to a velocity of delta (6-2) m/s = 4 m/s so the energy needed...

Can someone please explain what's going on at 47:40 Thanks in advance.

I am confused about time dilation. I understand that a common pedagogical device used is a light clock, in which a pulse of light flashes back and forth between two objects. I understand that when an observer in a vehicle carrying such a contraption is moving, to an external observer, as the...

Hi. I'm confused about degeneracy in I-D As far as I understand it ( and please tell me if I'm wrong ) ; a free particle is doubly degenerate with a continuous energy spectrum with eigenfunctions eikx and e-ikx. A particle on a ring in I-D is doubly degenerate but this time the energy is...

Hello, This is not a homework but I’m confused about current and voltage. My understanding is fragile and I need to reinforce it with your help. Below I’ve written what I think I know to be correct. Please correct me where required. This is high school physics.(i) Current is the...

Homework Statement The electron density per area, ##N## for a gas layer of thickness 10 cm can be determined $$n = k \times p \times 2.47 \times 10^{19}$$ For each adjacent sets of pressure data using Matlab, calculate the average energy in keV, the pressure difference in hPa, the energy...

Homework Statement $$ln(x^2)=4$$ Homework Equations ##a^{log_a(x)}=x## ##log_a(a^x)=x## The Attempt at a Solutionln(x^2)=4 <=> ##2ln(x)=ln(4)## <=> ##ln(x)= [ln(4)]/2## <=> ##log_e(x)= [ln(4)]/2## <=> ##e^{ln(4)/2}=x## <=> ##[e^{ln(4)}]^{1/2}## <=> ##sqrt(e^{ln(4)})##...

So I am reading a handout on transfer functions, and I got to this one example that doesn't seem right to me - which usually means I'm missing something. It looks like this: My understanding is that the numerator in H(s) is supposed to be the laplace transform of the input for the...

What exactly is the difference between something like (XY)2 and 2XY? I get that the 2XY would indicate 2 moles of XY, but I don't see why (XY)2 wouldn't be the same thing, so long as the whole formula is surrounded by parenthesis? thanks for any help

I seek from an SF writing point of view some much-needed clarification about solar flares, in particular their shortwave radiation components. So, given that x-rays, gammas and the like, propagate through space at light-speed - along with the rest of the electromagnetic spectrum - I take it then...

There a simple math example that I am confused ##(\sqrt {-4})^2## Theres two ways to think 1-##\sqrt {-4}=2i## so ##(2i)^2=4i^2## which its ##-4## 2-##\sqrt {-4}##.##\sqrt {-4}##=##\sqrt {-4.-4}=\sqrt{16} =4## I think second one is wrong but I couldn't prove how, but I think its cause ##\sqrt...

Homework Statement The problem is from D'Inverno's book on GR, problem 5.6. We're using the Jacobian/transformation matrix to convert the tangent to a circle centered at the origin of radius A from Cartesian to polar coordinates. I can do the problem and get the book answer, that's okay...

Homework Statement Darryl drives his load of tomatoes 14.0 km [E], 6.0 km [N], 12.0 km [N 15° E], and then 2.0 km [N 65° E]. This takes him 42 minutes. Calculate Darryl’s distance and displacement. Then draw a diagram to show your work. [/B]Homework Equations Not really sure.[/B]The Attempt...

Homework Statement A vacuum photodiode detector utilizes the photoelectric effect to detect light. The photoelectric effect causes electrons to be ejected from a metal plate when photons of light are absorbed by the metal. The energy of a photon is given by the equation E = hf, where h = 6.6 x...

How can light flux decrease after traveling in a medium without scattering it? Does attenuation mean scattering? Also in Infrared spectroscopy, why does the intensity of light decrease when the molecule is vibrating in resonant frequency? Does the electron produce an E field opposite to the...

Let's say a spaceship zooms around the Earth repeatedly at 99.99% of the speed of light for a period of time that is 50 years for observers on Earth. How much time will the passengers on board feel has elapsed after these 50 years? And, if someone on Earth was somehow able to remotely observe...

If there were 2 observers, 1 at rest with CMB, and the other falling into a black hole, how much time passes for the observer at rest with CMB while the other falls past the event horizon? I ask because I keep reading that time dilation (due to gravity) will cause the object falling into appear...

i'm new to statistical mechanics and the more I read and view ,the more I get confused. So far I've got this. At equilibrium a system will have a fluctuating energy,and the specific energies follow Boltzmann's distribution. I also read that within one phase point the molecular velocities also...