Position Definition and 1000 Threads

Homework Statement Lawrence is holding a 9kg dumbbell in his hand with his elbow flexed 90degrees. The horizontal distance from the center of mass of the dumbbell to the center of Lawrence's elbow is 33cm. The horizontal distance from the insertion of his elbow flexor tendons to his elbow is...

Consider a potential well in 1 dimension defined by $$ V(x)= \begin{cases} +\infty &\text{if}& x<0 \text{ and } x>L\\ 0 &\text{if} &0\leq x\leq L \end{cases} $$ The probability to find the particle at any particular point x is zero. $$P(\{x\}) = \int_S \rho(x)\mathrm{d}x=0 ;\forall\; x \in...

Why does measuring the position of a particle change its momentum? Is it because 'measuring' involves shooting EM waves or other particles at the particle, which changes its momentum?

Okay, first of all, I'm not very good at maths, so I will have to talk in programmer terms here. I have the following issue: A small rocket is moving in space, and I want it to move to and stay at a location in space, similar to a quadcopter. No as far as I see it, I have the following variables...

If the Big Dipper goes around once every 24 hours, why is it in a different position at midnight in December contrasted with midnight in June?

I am weeks away from submitting my PhD thesis (hep physics) and would like to carry on as a postdoc. However, I have made no applications so far because the job advertisements stipulate a 'statement of research interests'. This is a problem because I don't really have them. I don't mean that I...

Greetings all ! I really hope this is the right sub-forum for my question, I have chosen it because I've seen TLE being mentioned a couple of times around here. I have done some reading on astrodynamics and orbital mechanics, but I am relatively new to coding. I would like to write some C++...

Hi, I want to calculate the position-wave-function of a system of two free electrons with momenta k1 and k2 (vectors). 1. Homework Statement So, I want to have Psi_(k1,k2)(x1,x2) for a state |k1,k2> I also know that <k'|k> = (2Pi)^3 Delta(k-k') The Attempt at a Solution I tried the...

Might be simple but I couldn't see. We can easily derive momentum operator for position space by differentiating the plane wave solution. Analogously I want to derive the position operator for momentum space, however I am getting additional minus sign. By replacing $$k=\frac{p}{\hbar}$$ and...

Homework Statement The title, and assume that t=0, x=0 and v=0. Homework Equations Kinematic equations, and area of triangle and rectangle. The Attempt at a Solution I see what I did wrong with the part that is circled "parabola", as it should be just a straight line, but I am lost as to...

Homework Statement the minimum distance for a car traveling at a speed of 30m/s is 60 m, including the distance traveled during the driver's reaction time of 0.44s. what is the minimum stopping distance for the same car traveling at the speed of 41m/s? v=30m/s, s=60m drivers' reaction time =...

Homework Statement 2. The attempt at a solution I would use the arctan (Position j / Position i) and set it equal to the position vector. Then I would substitute values from the graph to find the variables. The solution manual, however, takes the derivative of the position vector and then...

I'm having some difficulties with a certain commutator producing inconsistent results. Specifically I'm referring to [p_x,x^3] Depending on how i expand this it seems i get different coefficients, i.e [p_x,x^3]=[p_x,x]x^2+x^2[p_x,x]=-i\hbar x^2 -x^2i\hbar=-2i\hbar x^2 However...

Homework Statement Place a third charge q between two charges Q1 = -2Q and Q2= 3Q so they stay in electrostatic equilibrium. Knowing that the distance between Q1 and Q2 is equal L Homework Equations (KQ1Q)/(QQ1)2 = (KQ2Q)/(QQ2)2 3. The Attempt at a Solution Let's start by saying that i know...

Homework Statement The position of a particle moving along the x axis varies in time according to the expression x = 6t2, where x is in meters and t is in seconds. Evaluate its position at the following times. (a) t=2.5s (b) t=2.5s + Δt (c) Evaluate the limit of Δx/Δt as Δt approaches zero to...

Homework Statement Suppose a can, after an initial kick, moves up along a smooth hill of ice. Make a statement concerning its acceleration. A) It will travel at constant velocity with zero acceleration. B) It will have a constant acceleration up the hill, but a different constant acceleration...

Homework Statement A car starts from rest and accelerates uniformly at 3.0 m/s2. A second car starts from rest 6.0 s later at the same point and accelerates uniformly at 5.0 m/s2. How long does it take the second car to overtake the first car? Homework EquationsThe Attempt at a Solution So let...

If I got the general idea correctly, Bohmian mechanics is completely deterministic regarding particle positions. But can it also do the same for spin or polarization? How does entanglement work out in it, considering that it should be able to give predictions along any measuring angles, not just...

Homework Statement Graphically and mathematically model the relationship between position and the time for a motorized lab car. The definition of position my teacher gave us is: "Where an object is located with respect to a coordinate system. (measured in meters)". Everyone else in my class...

Let's say that I have a stick with weight evenly distributed throughout. I attach a fan to one end of the stick, then balance it from its new centre of mass. I measure the distance from the ground to the stick then drop it. The stick tilts up towards the side generating more air resistance (fan...

Homework Statement Indicate the positions of the planets in the sky at the times given. I am struggling on how to answer these questions any help would be great any help would be great. thanks pf! The Attempt at a Solution 1) Jupiter at eastern quadrature around sunset? Jupiter...

Homework Statement Consider the electron on a six site chain. The Hamiltonian is: ## H = \begin{pmatrix} 0 & -1 & 0 & 0 & 0& 0\\ -1 & 0 & -1 & 0 & 0& 0\\ 0 & -1 & 0 & -1 & 0& 0\\ 0 & 0 & -1 & 0 & -1& 0\\ 0 & 0 & 0 & -1 & 0& -1\\ 0 & 0 & 0 & 0 & -1& 0\\...

$r(t)=sin(t)$i $+ 2cos(t)$j $t= \pi/4$ sketch the position vector and the tangent vector $r'(t)=cos(t)$i $- 2sin(t)$j $r(\pi/4)= \frac{\sqrt{2}}{2}$i $+ \sqrt{2}$j $r'(\pi/4)= \frac{\sqrt{2}}{2}$i $- \sqrt{2}$j $\left\langle \frac{\sqrt{2}}{2}, \sqrt{2} \right\rangle$ $\left\langle...

Is there such a electronic device that measures the current Longitude and Latitude of your current position on the Earth?

A particle P is moving with a const. speed of 6m/s in a direction 2î - j - 2k. When t=0, P is at a point with position vector 3i + 4 j -7k. Find the position vector of P after (1) t seconds (2) 4 seconds. The solutionnstates that ' change the particle speed is constant and is a long text...

Hello PF! I wish to do research as an undergrad, so I am thinking of sending emails to professors to ask for any available positions. What would be the most professional way to do this? Thanks in advance,

Homework Statement A sphere of radius 12.0cm has refractive index of 1.33. A speck is 4.0cm from the centre of the sphere is viewed along the diameter that passes thru the speck. Find the position of image when the speck is viewed from the nearer side? the ans is -7.2cm Homework Equations...

When a particle's position is measured, does the wavefunction collapse to the eigenstate of the measurement (a delta function), or do you account for the accuracy and precision of the measurement device by making the state be a mixture of eigenstates corresponding to the device's imperfect...

Hi guys!, I am in a kind of dilemma and wanted to know your opinion. I am from a very small european country and came to US for a PhD in a respectable university (top 50 in all world rankings). I just finished my PhD in mathematical modeling of turbulent flows and applied for different...

Dear all, I solved the Navier-Stokes equations in Eulerian description. I would like to illustrate it as follows: I thought to place particles in the domain which will characterize the fluid flow. However I must know the particle position in the Lagrangian specification. As I place the...

Homework Statement Find the eigenfunctions of a particle in a infinite well and express the position operator in the basis of said functions.Homework Equations The Attempt at a Solution Tell me if I'm right so far (the |E> are the eigenkets) X_{ij}= \langle E_i \vert \hat{X} \vert E_j \rangle...

Homework Statement Hello, I need to calculate the expectation value for position and momentum for a wavefunction that fulfills the following relation: ψ0(-x)=ψ0(x)=ψ*0(x) The wave function is normalised. Homework Equations There is also a second wave equation that is orthogonal...

Homework Statement Hi, this isn't a homework question but one that I think has bothered not just me... According to most sources out there an electron and a positron annihilate when they 'collide' or 'encounter' each other, however we also know that the position of an electron or positron...

When using Fourier's trick for determining the allowable energies for stationary states, Griffiths introduces the a+- operators. When factoring the Hamiltonian, the imaginary part is assigned to the momentum operator versus the position operator. Is there a reason for this? If : a-+ = k(ip +...

After reading an article on Planck length, I began to wonder whether or not the theoretical limit implied that position could be quantized in whole integer multiples of Planck length? To demonstrate what my question is asking mathematically I hope you will scrutinize the equations below: If...

Say I have the following matrix, written in Mathematica A := {{a11, a12, a13, a14}, {a21, a22, a23, a24}, {a31, a32, a33, a34}, {a41, a42, a43, a44}}
 I want to exchange the positions of a12 and a21, a14 and a23, a32 and a41 , a34 and a43. Any ideas? Thanks.

Hi all, I came across the term placement, and presentment and the likes. I was wondering what they may mean in physics. I tried a search but the answers were not very clear. I was also wondering what action means in physics. Any answers will be appreciated. Thanks

How do I calculate the percentage error between a guess of a position in 3D space, and the actual position. For example, if I am allowed an error of 100mm in the x, y, and z directions, in a 5m x 4m x 3m volume, what is the maximum percentage error allowed? Can I just do...

Homework Statement Find the eigenfunctions and the eigenvalues of the following Hamiltonian \hat{H} = \frac{1}{2m} \left ( \frac{ \hbar}{i} \vec{\nabla}-\frac{q}{c}(0, B_z x,0) \right ) ^2 = \frac{1}{2m} \left ( - \hbar^2 \vec{\nabla}^2-\frac{\hbar q}{ic}(\vec{\nabla}·(0, B_z\hat{x},0) +...

Homework Statement I am trying to solve Problem 21 from this sheet: Homework Equations The equation describing the time evolution of operators is given in the problem. The Attempt at a Solution I have found the commutators of the position and momentum operator with the...

Hello everyone :) I am going to finish my master thesis in physics ( Nano-science ) in Germany at rostock university within the next two months, and i would like to apply for PhD in other city. I am not a German. I would like to ask, whether it is very difficult to get a PhD position in...

Homework Statement The position s (in metres) of a particle, as a function of time t (in seconds), is described by the equation s=5i+4r^2j. i and j are perpendicular unit vectors. a) Calculate the position of the particle at t=5. b) Determine the particle's average velocity between t=0 and...

Homework Statement A portion of helium gas in a vertical cylindrical container is in thermodynamic equilibrium with the surroundings. The gas is confined by a movable heavy piston. The piston is slowly elevated a distance H from its equilibrium position and then kept in the elevated position...

Hello I know acceleration of a pendulum as a function of angle. Can I find velocity by integration with respect to theta? My intuition says yes, but dimensional analysis tells me otherwise. What is right and wrong? And what about work? Can I integrate tau = Ia with respect to theta and find...

¿Is there an unique wavefunction for a system if we know the distribution probability function for variables from the system and first derivatives from these variables and we have the gauge fixed (by external impositions not related with the wavefunction knowledge obviously? (Nothing about...

Ever since learning about atoms and molecules as a child I have envisioned substances (air, water, metal, etc) as being composed of discrete individual atoms and molecules. Today it occurred to me that might be an oversimplification, especially for gasses in which molecules are free to move...

Homework Statement The function x = (7.4 m) cos[(5πrad/s)t + π/5 rad] gives the simple harmonic motion of a body. At t = 6.2 s, what are the (a) displacement, (b) velocity, (c) acceleration, and (d) phase of the motion? Also, what are the (e) frequency and (f) period of the motion...

The position vector ##\vec{r}## in cartesian coordinates is: ##\vec{r} = x \hat{x} + y \hat{y}##, in polar coordinates is: ##\vec{r} = r \hat{r}##. But, given a curve s in somewhere of plane, with tangent unit vector ##\hat{t}## and normal unit vector ##\hat{n}## along of s, exist a definition...

I want to ask how will the equilibrium position of the system change if water is added to the system?

I'm in the process of job hunting right now and I'm trying to obtain an actuarial position. Looking to hear if any actuaries here have any suggestions or tips on how to increase my chances. Right now, I"m just looking through job searching sites like indeed and monster, and also going to...