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3
votes
1answer
89 views

Work done by vibrating string

figure from http://webusers.physics.illinois.edu/~m-stone5/mma/notes/amaster.pdf The string has fixed ends, a mass per unit length of $\rho$, and is under tension $T$. This source claims that "the ...
-2
votes
1answer
3k views

Net flux calculation through a cube [closed]

Ans: Applying Gauss’s law the net flux can be calculated. And for option (B), I guess the flux will be 0. But not sure. Can anyone explain all the 3 options? For left and rignt face, EA = ...
5
votes
7answers
2k views

If the net work on a particle is zero, can the speed change?

The following question was on a quiz in physics class: If the net work done on a particle is zero, which of the following statements must be true? a) The velocity is zero b) The velocity is ...
1
vote
2answers
350 views

Wave function decomposition

Problem: Given the wave function $\Psi_0=A\sin^2(\theta)$ along with the Hamiltonian operator of a physical system: $H=\frac{L^2}{2I}+g B L_z$, find the eigenvalues and eigenfunctions of $\hat{H}$ ...
2
votes
2answers
126 views

How to determine which one would not be the resultant?

i had a physics exam yesterday, which was all in all pretty good except for this one question which i just don't get.: ...
3
votes
1answer
664 views

Calculating Expected Systematic Error in a Pendulum Experiment

I am a little confused by part c of problem 4.28 of Taylor's Introduction to Error Analysis book. A student measures the acceleration due to gravity by using a steel ball suspended by a light string. ...
1
vote
2answers
783 views

Prove $[A,B^n] = nB^{n-1}[A,B]$

I am trying to show that $[A,B^n] = nB^{n-1}[A,B]$ where A and B are two Hermitian operators that commute with their commutator. However, I am running into a little problem and would like a hint of ...
1
vote
0answers
92 views

Understanding unit vectors

Trying to understand how the unit vector ${\mathcal{\hat{r}}}$ defined as $\frac{r' - r}{|r' - r|} $ (where $r'$ is the source point) works in this problem: Work out the electric field, $E$, at point ...
2
votes
2answers
222 views

Proper time for an accelerating object

As far as I have read so far, proper time is the time measured on the clock of an inertial frame moving uniformly with respect to another inertial frame. The concept and the mathematical expression ...
-1
votes
1answer
380 views

Electric circuit question [closed]

http://www.fisme.uu.nl/nno/opgaven/bestanden/Ronde1-Theorie-2009.pdf, question 5: You have to calculate Id when the switch at S is opened, when its closed, the Id = 0.5 A. All resistors are ...
-1
votes
1answer
2k views

Finding the point of collision between two objects when acceleration is constant

$\newcommand{\accunit}{\mathrm{m}/\mathrm{s}^2}$ A coin is dropped 60.0m above the top of an elevator car. The coin is dropped just as the car begins to move upwards. The elevator first ...
0
votes
1answer
56 views

Uniform Acceleration [closed]

A steel ball is allowed to roll from rest down a 20.0 m long slop and over a 25 m long level surface. It takes 4.0 seconds to roll down the slope. Calculate the speed at the bottom of the slope. ...
0
votes
2answers
117 views

Waterflow of coolant in nuclear reactor [closed]

The generator in a nuclear reactor delivers 580 MW electric power. a) How much TWh electrical energy is delivered yearly if the reactor runs only 70 % of the time? b) What flow of coolant ...
2
votes
1answer
97 views

Textbook Problem: Free energy expression

In Klotz, Introduction to Chemical Thermodynamics, Ex. 8.2 requires me to derive $$ dG = V \left( \frac{\partial p}{\partial V} \right)_V dV + \left[ V \left( \frac{\partial p}{\partial T} ...
0
votes
2answers
731 views

Friction problem having two blocks on separate inclined planes connected by a string

This is a question I found in my old high-school textbook(I'm revising the topics for a course).Two blocks A and B of masses $1kg$ and $2kg$ are placed on a fixed triangular wedge by a massless ...
1
vote
1answer
1k views

Calculate Mass based on Velocity and Acceleration

I am attempting to design a obstacle avoidance system with the Arduino. My position (for now) is going to be stationary. I will be detecting an incoming object and I want to use the below known ...
1
vote
1answer
64 views

Bug in linear thermal expansion, $L_0$ must be $0$

Assume we change the temperature of an object with negligible size in $2^{nd}$ and $3^{rd}$ dimensions from $T_0$ to $T_1$ to $T_2$, with all of them pairwise different. We choose a substance with ...
1
vote
1answer
222 views

Circular motion question

(Q) Find the maximum speed at which a truck can safely travel without toppling over, on a curve of radius 250m. The height of the centre of gravity of the truck above the ground is 1.5m and the ...
-1
votes
1answer
260 views

Electric field of an infinitely long (thin) metal cylinder [closed]

An infinitely long thin metal cylinder of radius $a$ coaxial with the $z$ axis carries a uniform surface charge density $\sigma=\frac{\lambda}{2\pi a}$, where $\lambda$ is a constant. A thick ...
1
vote
2answers
1k views

Calculate electric potential and electric field of uniformly charged wire

Say you have a uniformly charged straight wire of length $2L$ going from $-L$ to $+L$ along the $z$ axis with its midpoint located at $z=0$. What is the electrostatic potential, in cylindrical ...
2
votes
2answers
2k views

How can I calculate the pressure against the sides of a container? [closed]

While answering this question on DIY.SE, I wanted to calculate the amount of pressure (in psi) that would be exerted on the walls of the container. However, I don't know much about how to calculate ...
3
votes
1answer
1k views

Riemann tensor in 2d and 3d

Ok so I seem to be missing something here. I know that the number of independent coefficients of the Riemann tensor is $\frac{1}{12} n^2 (n^2-1)$, which means in 2d it's 1 (i.e. Riemann tensor given ...
1
vote
0answers
70 views

An Equality in The Calculus of Many Instantons

I am reading the review on instantons. When I tried to derive formula (2.27) on page 17, I always get the different coefficient of $gF_{mn}$ term. My calculation is just directly expanding the first ...
0
votes
1answer
169 views

Derive conservation law using divergence theorem

Material scientists have discovered a new fluid property called "radost" that is carried along with a fluid as it moves from one place to the next (just like a fluid's mass or momentum). Let ...
2
votes
1answer
176 views

Dog running after sephard

Assume there is a dog A on a field and a sephard B. B moves on straight line with constant ...
1
vote
2answers
734 views

Must a reversible engine be a carnot engine?

I have this homework question: "Show that any reversible engine operating between T1 and T2 is a carnot engine." I think I have a solution, but it feels very hand-wavy. We know that any process that ...
3
votes
4answers
535 views

The Expansion Coefficients for a Particle in a Box

This is an expansion of two previous questions I had before (I am very confused by it). I am now encountering a problem with an integral. We want a general expression for the probability of finding E. ...
1
vote
2answers
259 views

Quantum Number of a Tennis Ball

A tennis player has a tennis ball container with a single ball in it (it normally holds three). He shakes the tennis ball horizontally back and forth, so that the ball bounces between the two ends. We ...
0
votes
2answers
1k views

Two masses connected by a string in horizontal frictionless table

Suppose that two masses with different mass are connected by a string in horizontal frictionless table. Then when there is equal acceleration for two masses, string force would extend in some ...
1
vote
0answers
130 views

insulator based gauss law questions

My book is incredibly scarce on insulator based Gauss law questions. Conductors seem to handle themselves pretty simply. Here's a question I'm working on that isn't part of my book. where the radii ...
-1
votes
1answer
195 views

Normalizing a Wave Function

How would I normalize the wave function: $ \psi (x)$ = $Ce^{i\rho_0x/\hbar}e^{-|x|/2\Delta x}$? I squared it, which got rid of the imaginary part-Then I considered breaking up the absolute value-but ...
1
vote
1answer
232 views

Finding mass density of a sphere?

If the gravitational field vector is independent of the radial distance within a sphere, find the function describing the mass density $\rho (r)$ of the sphere. I uses the divergence of $\bf ...
3
votes
0answers
157 views

Schwarzschild metric in a different coordinate system

In PADMANABHAN, Gravitation (Foundations and Frontiers), Cambridge, p $304$, exercice $7.6$, an example of the Schwarzschild metric in a different coordinate system is given : $$\mbox{d}s^2= ...
2
votes
2answers
201 views

Stable equilibrium given force

If a particle moves under the influence of a resistive force proportianal to velocity and a potential $U$, $$F(x,\dot x)=-b\dot x-\frac {\partial U}{\partial x}$$ Where b>0 and ...
4
votes
3answers
200 views

Finding the equation of motion of anharmonic potential [closed]

If I have a potential given by: $$U=U_0\left[2\left(\frac xa\right)^2-\left(\frac xa\right)^4\right]$$ It says that at $t=0$, the particle is at the origin ($x=0$) and the velocity is positive and ...
0
votes
1answer
120 views

Probability in moving from state $\lvert1\rangle$ to $\lvert2\rangle $ [closed]

The system is $|1\rangle$ at time $t = 0$, while $|2\rangle$ at time $t$. The base is orthonormal $\left\{|1\rangle, |2\rangle\right\}$. Epsilon and delta are positive constants, which have some ...
-2
votes
1answer
554 views

How can you prove generalised Jacobi identity? [closed]

This $$[A, [B,C]] + [C, [A,B]] + [B, [C,A]] = 0$$ This proof is not wanted, since there is an attachment of some variables. How can you prove the equation?
1
vote
1answer
90 views

Commutation of abstract $O(3)$ generators and vectors

I've been given the following problem, and I'm quite lost with it. Let $L_1$, $L_2$, and $L_3$ denote the abstract o(3) algebras. You are given that $\vec{A} = (A_1, A_2, A_3)$ and $\vec{B} = (B_1, ...
0
votes
1answer
875 views

Relationship between angles [closed]

Question: Find the relationship between angles $\theta$ and $\phi$ using the equations of equilibrium and solve for $\theta$. Express your equation for $\theta$ in terms of $\phi$. ...
0
votes
1answer
70 views

Vector Isolation/ Rotation

I have a series of vectors (current speeds) based on an ENU (East North Up) system. I would like to estimate the current speed of the water headed in a specific direction. In this example I am ...
4
votes
1answer
378 views

Plastic bottle floating and sinking

I was doing this experiment: i take a plastic cup, put in a container of water, it floats – then when I put a coin in the water, it sinks and rests at the bottom. So to make the cup sink, i fill it ...
1
vote
0answers
84 views

Find contact force given sphere's radii and distance

I simulate scenario of two contacting elastic spheres, where their radii and the distance of their centers is known, and repulsive force should be computed. Material parameters are also given. Most ...
8
votes
3answers
686 views

Bird flying in a cage

Assume that you are holding a cage containing a bird. Do you have to make less effort if the bird flies from its position in the cage and manages to stay in the middle without touching the walls of ...
0
votes
1answer
1k views

Projectile motion, what is the relation between initial angle and speed at a given distance [closed]

I am trying to understand the relation between the initial angle of a projectile and its initial speed, given that the distance this projectile will travel is fixed and at the same height as the ...
0
votes
0answers
259 views

Angular Frequency about stable equilibrium

So I have the potential energy defined as: $$U(x)=U_0[2(\frac xa)^2-(\frac xa)^4]$$ And I want to find the angular frequency of oscillations about the point of stable equilibrium. I found the point ...
0
votes
1answer
276 views

Simple Acceleration Problem throwing me off

I am having trouble with this problem from my homework. I have gone over it many times, and I must have some concept wrong. A rocket is launched from the ground with constant acceleration. After 4 ...
1
vote
2answers
2k views

Geometric Structure Factor for Monatomic FCC lattice

I am trying to find the geometric structure factor and my work here is clearly wrong. I will put my wrong answer and then I will throw up the link to wikipedia for the correct answer, because I cannot ...
-5
votes
2answers
1k views

Finding the period of an infinite length pendulum [closed]

What would be the period of a pendulum with an infinite length, assuming a non-rotating Earth? The answer is not infinity.
1
vote
3answers
276 views

$\mathrm{Tr}(XY) = \mathrm{Tr}(YX)$?

I'm trying to understand the Dirac notation to understand quantum mechanics better. I'm trying to show the above relation using the Dirac notation. Given $$\mathrm{Tr}(X)~=~\sum_j\langle ...
1
vote
1answer
1k views

Energy and probability for the particle in a box

The question statement: we have a particle of mass m in a box of length a. The wavefunction is given as $$\psi(x)=x\sin \left(\frac{\pi x}{a}\right)$$ It asks to normalize the wave function and find ...