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 questions.

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1answer
251 views

Fluid Dynamics: Bernoulli Air Tunnel

I have the following question as part of a lab intro to explain the more complicated stuff I'l actually have to submit in the lab. I put all the questions here just to show my thought pattern/what ...
2
votes
1answer
819 views

Free Body Diagram of Fluid Statics Problem

I need help determining the forces, and the direction of them in this fluid statics problem. A hollow cylinder with closed ends is 300mm in diameter and 450mm tall. It has a mass of 27kg and a tiny ...
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0answers
73 views

How do I find the frictional force using a free body diagram? [duplicate]

Possible Duplicate: Free Body Diagram I have this problem: A person push a 16 kg lawn mower at constant speed with a force of 80 Newtons directed along the handle which is at an angle ...
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2answers
711 views

What is a Free Body Diagram?

I have this problem: A 10 kg box is resting on a frictionless table and someone drags it by a string at a 30 degree angle to the horizontal with a force of 40 Newtons. Find the acceleration of the ...
2
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2answers
1k views

What is the potential difference between point X and point Y?

Here is the problem: In the above figure I want help on finding the potential difference between X and Y. It is getting quite confusing due to the battery in the middle. I found the current in both ...
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3answers
406 views

Problem with an electricity / thermodynamics assignment

I've been trying to figure this one out for a while on my own, so I'd like to ask for your help if you could offer some. The task states: A heater made out of a wire with a diameter $R = ...
1
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1answer
286 views

Vertical Motion in Air + Density [closed]

I am having trouble with this confusing question. Please help. The fastest recorded skydive was by an Air Force officer who jumped from a helium balloon at an elevation of 103000 ft, three times ...
0
votes
1answer
143 views

Showing that a given matrix provides the desired Lorentz transformation

I am working on problem 5.12 in Halzen and Martin’s Quarks and Leptons. We are asked to show that the matrix $$ S = 1 - \frac{i}{4} \sigma_{\mu \nu} \varepsilon^{\mu \nu} $$ represents the ...
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3answers
4k views

Convert acceleration as a function of position to acceleration as a function of time?

Suppose I have acceleration defined as a function of position, $a(x)$. How to convert it into a function of time $a(t)$? Please give an example for the case $a(x)= \frac{x}{s^2}$.
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0answers
489 views

Amplitude of a Forced Harmonic Oscillator

For an assignment in one of my maths units at uni, I've been asked to derive and solve the differential equation of motion for a forced harmonic oscillator, with the forcing function having the form ...
2
votes
1answer
778 views

infinite parallel conducting planes

two infinite parallel conducting planes grounded and are separated by a distance d. place a point charge "q" between the two planes, using the "green teoerma reciprocity" how I show that the total ...
2
votes
1answer
626 views

Superposition of wavefunctions

Suppose you have 2 normalized wavefunctions $\psi_1=Ne^{iax}e^{if(x)}e^{i\omega t}$ and $\psi_2=Ne^{-iax}e^{if(x)}e^{i\omega t}$ defined on $x\in [-x_0,x_0]$ and vanishes for $|x|>x_0$. What then ...
2
votes
1answer
336 views

Finding Speed with the Energy Principle - Nuclear Fission

The question goes along the lines: Uranium-$236$ fissions when it absorbs a slow-moving neutron. The two fission fragments can be almost any two nuclei whose charges $Q_1$ and $Q_2$ add up to ...
4
votes
1answer
1k views

Hooke's Law question

I have the following question to answer: a force of160 N stretches a spring 0.050m from its equilibrium position. A. what is the spring constant of the spring? The equation for Hooke's Law in my ...
4
votes
1answer
936 views

Infinite-range 1D Ising model + Hubbard-Stratonovich-Transformation

I have a probably quite simple question RE the HST. After some work, I obtain as the partition function for the infinite range 1D Ising model $$Z = \int_{-\infty}^\infty \frac{dy}{\sqrt{2\pi / ...
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2answers
435 views

How do you choose the locations of forces when calculating moments?

A uniform bridge of weight 1200kN and of length 17m rests on supports at each end which are 1m wide. A stationary lorry of weight 60kN has it’s centre of mass 3.0m from the centre of the bridge. ...
3
votes
4answers
325 views

How are we able to view an object in a room with bulb..?

This is a very basic question on optics. How are we able to view an object kept in a room with a bulb? From what I understand, light rays from bulb will hit the object and some colour will be ...
3
votes
1answer
494 views

How to set up a very simple experiment in optics?

This might come across as a very rudimentary question. My fundamentals of Optics are weak. In the optics chapter of my physics text book I saw diagrams each depicting an object on the left and a lens ...
3
votes
2answers
677 views

How do I calculate the position on the Bloch sphere of a quantum gate with a given diagonal matrix?

In quantum computation there are several principal quantum gates that have corresponding matrix representations. One of these is the Z gate, whose matrix is $\left[\begin{smallmatrix} 1 & 0 \\ 0 ...
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votes
1answer
11k views

How do you find the uncertainty of an weighted average?

The following is taken from a practice GRE question: Two experimental techniques determine the mass of an object to be $11\pm 1\, \mathrm{kg}$ and $10\pm 2\, \mathrm{kg}$. These two ...
0
votes
1answer
311 views

Fluid Mechanics Problem - Ball in Reservoir

I'm having a problem starting and solving the following problem: My attempt at the solution was to realize you need to balance the upward forces with those of the downward forces in which case you ...
2
votes
1answer
5k views

Best way to solve P-V-T Question

Typically in an exam or problem set we have a problem that's like this: Determine the specified property at the indicated state of water. Locate the state on a sketch of the T-v and P-v diagram. p= 3 ...
0
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1answer
342 views

Calculating vector of plane resulting from tailwind

In some basic physics homework I have, it asks what the resulting vector would be for a plane traveling at x m/s in y direction that is affected by a tailwind going in z direction at w m/s. How would ...
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3answers
151 views

Question about orthonormal decompositions over unitary operators

I'm teaching myself quantum information theory using Nielson and Chuang's "Quantum Computation and Quantum Information" and I'm at a point in the book where the formalism is starting to make my eyes ...
2
votes
4answers
36k views

Heat transfer calculated from the specific heat formula

Say I have 10g of silver, whose specific heat is known to be 0.235. I've heated it up from 50.0C to 60.0C. How much heat has been transferred? The equation is: $$ Q = C_pm\Delta t $$ where Cp is ...
3
votes
1answer
3k views

Reversible adiabatic expansion

I am confused with adiabatic expansions. I have a homework problem wherein 2.75 moles of an ideal gas at 375 K expands adiabatically with an initial pressure of 4.75 bar and a final pressure of 1.00 ...
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2answers
2k views

Calculating uncertainty in the final result (combining uncertainties)

I'm struggling to determine the uncertainty in $F$ so it would match the textbook answer. The problem statement is: A force F is obtained using the equation: $F = \frac{mv^2}{2\pi(x_2 - x_1)}$. The ...
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2answers
6k views

Not sure of a homework solution involving average acceleration

A 50.0 g Super Ball traveling at 25.0 m/s bounces off a brick wall and rebounds at 22.0 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 3.50 ms, what is the ...
3
votes
2answers
583 views

Paramagnet: Negative specific heat?

for a simple paramagnet ($N$ magnetic moments with values $-\mu m_i$ and $m_i = -s, ..., s$) in an external magnetic field $B$, I have computed the Gibbs partition function and thus the Gibbs free ...
3
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4answers
997 views

How can I explain why the weak nuclear interaction between individual nucleons is 'weak'?

By considering the energy-time uncertainty principle, estimate the range of the weak nuclear interaction at low energies. Compare this range to the size of a typical nucleon (for example, a proton) ...
4
votes
2answers
112 views

Balmer lines and their positions

I have two stars, both of which have Balmer lines at the same wavelength positions. The depths of the Balmer lines on each star are different, and the stars are different as well. Why does this ...
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4answers
5k views

Why do we test electric fields with positive charges and not negative ones?

Is there any difference between using a positive versus a negative charge to test an electric field?
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2answers
237 views

Can the process $u\overline{u} \rightarrow s\overline{s}$ be mediated by the EM interaction?

I’m working on a homework problem which asks for the dominant contribution (e.g. EM, strong, or weak) to the process $p + \overline{p} \rightarrow \Lambda + \overline{\Lambda}$). I know that the EM ...
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vote
2answers
448 views

Vectors, Component Addition, and Significant Figures

I have two vectors $\vec{A}$ and $\vec{B}$ and I need to find the x- and y-components of $\vec{C} = \vec{A} + \vec{B}$. Here's what I have so far: $$|\vec{A}| = 50.0 \mathrm{m}, \theta = ...
6
votes
2answers
778 views

How do Leptons arise from Lambda decay?

I have a question for an assignment: Use your understanding of the quark model of hadrons and the boson model of the weak nuclear interaction to explain how leptons can arise from lambda decay, ...
3
votes
1answer
217 views

Equation of Motion in a Non-Inertial (Rotating) Frame

Let me preface my question by informing you this is for an assignment, so I would rather not have explicit answers but rather be given guidance in arriving at the correct solution. The question is ...
0
votes
1answer
617 views

Changing magnetic flux graph?

In regards to a graph of the changing magnetic flux in a generator such as this one: a) The equation of the graph should be $\Phi = BA \cos \theta$. As $\theta=\omega t$ (angular velocity*time), ...
6
votes
2answers
339 views

Conservation of energy in a non-linear oscillator

I have a homework question about a "non-linear oscillator". I actually have an answer to this question, but the answer I get is stronger than what is needed according to the question. The question ...
2
votes
1answer
3k views

Degeneracies of the first excited state

I have a box with $x,y,z$ all ranging from 0 to $l$. It has $V(x)$=0 inside and =$\infty$ outside. By extending the 1D Schrodinger equation, I have that the allowed energy eigenvalues are ...
4
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1answer
284 views

Projection of states after measurement

Continuing from the my previous 2-state system problem, I am told that the observable corresponding to the linear operator $\hat{L}$ is measured and we get the +1 state. Then it asks for the ...
0
votes
1answer
345 views

Two-state system problem

Given a 2-state system with (complete set) orthonormal eigenstates $u_1, u_2$ with eigenvalues $E_1, E_2$ respectively, where $E_2>E_1$, and there exists a linear operator $\hat{L}$ with ...
0
votes
1answer
394 views

Functional Derivative of Convolution

How to carry out the following functional derivative? $$\frac{\delta F}{\delta n(r)}$$ where $$F=\int dr n(r) \int C(|r-r'|) n(r') dr'$$ is it simply: $$2 \int dr' C(|r-r'|) ...
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1answer
382 views

Representations of gamma matrices

I have to do this exercise for homework. Find a representation of the gamma matrices unitarily connected to the standard representation for wich the spinors $u(p)$ that satisfy the equation $(p_\mu ...
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0answers
342 views

Understanding 1D Kinematics and Uniform Acceleration? [closed]

So I was given the following homework problem: You land on an unknown planet somewhere in the universe that clearly has weaker gravity than Earth. To measure g on this planet you do the following ...
3
votes
3answers
3k views

Why is the central maximum the brightest?

This is a question directly from a homework sheet, however I can't find any decent answers online so hopefully someone can help! In single slit diffraction, why is the central maximum double the ...
2
votes
1answer
728 views

Lean angle of a turning bicycle

I'm asked to derive a relationship for the leaning angle of a bicycle with the following specs: Center of gravity for bike and rider is a distance $L$ above the ground when vertical, and the total ...
6
votes
1answer
573 views

Magnetic field from a half-cylinder [closed]

I am preparing for an exam, on this problem I had the opposite direction of the magnetic field. A conductor-cylinder with radius R has been cut in half ($\phi \in [0,\pi]$) A DC current $I$ runs ...
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vote
1answer
228 views

Lenz' law versus $-\frac{d\Omega}{dt}$

I am preparing for an exam, on one problem my answer differ from the solution. The current $i(t)=I_0e^{-\alpha t}$ runs in a long straight conductor along $\hat z$. Point A,B,C,D forms a triangle. ...
3
votes
0answers
173 views

Matter-wave interference from free falling cold atoms

and another exam question, this is about current research: Interference of matter waves has been studied using ultra-cold atoms. The phase of a matter wave for free-falling cold-atoms at time $t$ ...
3
votes
2answers
420 views

The quantized energy level E depends on which power of n?

A particle in one dimension moves under the influence of a potential $V(x)= ax^6$, where $a$ is a real constant. For large $n$, what is the form of the dependence of the energy $E$ on $n$?