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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15 views

momentum operator and uncertainty

I want to calculate expectation value of momentum vector(3d) using two ways, one is momentum space wave function and the other is p operator. I think the value is vec(p_0) but the result from ...
-2
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0answers
12 views

sonometer application.distribution of frequency along the length h [on hold]

the total length of a sonometer wire between fixed ends is 110cm.two bridges are placed to divide the lenght of wire in 6:3:2.the tension in wire is 400N and mass per unit lenght is 0.01kg/m.what is ...
0
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0answers
10 views

Induced EMF question. Not sure what I'm doing wrong.

The question: A circular conducting loop of radius 17.0 cm is located in a region of homogeneous magnetic field of magnitude 0.100T pointing perpendicular to the plane of the loop. The loop is ...
0
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0answers
14 views

Concept based on boltzmann constant [on hold]

A gas molecule of mass $M$ at the surface of the Earth has kinectic energy equal to 0 degree Celsius. If it were to go straight without colliding any molecules, how high would it rise? Assume that the ...
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1answer
14 views

Resolution of force vectors

For example in a simple pendulum problem.. the forces that act on the bob are tension and gravitational force. but while the resolving the vectors to find T(tension) at any given angle x with the ...
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0answers
8 views

SC or FCC lattice?

One problem in a course on solid state physics asked me to find the reciprocal lattice of the (110) plane of an Fe (BCC) lattice. This plane looks like a two dimensional FCC lattice: It is supposed ...
-2
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0answers
17 views

Simple Harmonic Oscillator [on hold]

How do I show that X, Y and Z are all solutions of the TISE for the 1D SHO? In addition to this, how may I find the eigenfunctions and eigenvalues for this system?
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1answer
68 views

Prove that $(e^{i\lambda A})^\dagger=e^{-i\lambda A^\dagger}$ [on hold]

Prove $$(e^{i\lambda A})^\dagger=e^{-i\lambda A^\dagger}$$ where $A$ is an operator. Can anyone explain how to go about this question? Writing it as a power series gets confusing. So basically I ...
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1answer
21 views

Stair well descent

I am trying to understand the science behind lowering a person down a flight of stairs on a sled. My tensile strength only says it can hold 250 pounds but I have seen it lower people that weigh 300 ...
0
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1answer
18 views

Relative acceleration question for pendulum [on hold]

http://postimg.org/image/t3x0s5wjh/full/ In this picture of an inverted pendulum, I am trying to find the acceleration of point G relative to O, using the formula. I wanted to know if the angle ...
0
votes
1answer
29 views

Thevenin equivalent circuit [on hold]

Obtain the Thevenin source form equivalent to the circuit in figure 2 assuming that points A and B are the source terminals of the Thevenin source. Could u explain it step by step?
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1answer
44 views

Product of deltas in kinetic second quantization hamiltonian

I am trying to derive the result for a kinetic hamiltonian in second quantization in term of the fields, that is: $\hat{H} = \int - \Psi^\dagger (r) \frac{\hbar^2\hat{\nabla}^2}{2m} \Psi(r)$ I start ...
-3
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0answers
23 views

I need a help in my homework please [on hold]

In a U tube containing mercury,we pour a quantity of water. If the height of the column of water is 13.6 cm, calculate the difference of levels between both surfaces of mercury in the two tubes.
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0answers
9 views

Roughness of the Surface and the time that a toy hovercraft hovers?

My question is about a toy CD hovercraft. I want to know that how does the time that the hovercraft hovers scale with roughness of the surface? Thanks in advance
0
votes
1answer
19 views

effort required to move the trolley [on hold]

the problem is, a 500kg load is supported on a trolley which has 4 wheels.i want to calculate the effort to be put in order to move the trolley. can someone help me with this problem?Assume data If ...
-1
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0answers
24 views

Generating hysteresis curve online [on hold]

For my final year project I have to design a code in which numbers from -10 to +10 are incremented in steps of 0.5. Using a code or model, I have to get a number. The graph between the two numbers ...
-1
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0answers
22 views

Color changing or becomes darker? [on hold]

Please read this question and tell me your idea . This question is different from WHY WET IS DARK? QUESTION : Clothes can look darker or change colour when they get wet. Investigate the phenomenon. ...
0
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2answers
38 views

Rocket Altitude Calculation

Assignment Basic data I was launching a rocket model and I tried to calculate the reached altitude. The engine (C6-0) impulse is 10 Ns Total weight is 65,7 g (includes the engine) I calculated ...
-2
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0answers
25 views

Shortest time to cross river [on hold]

A river is flowing at velocity $v$ and a man who can swim with velocity $u$ in still water wants to get across in the shortest possible time. We can find true velocity of man, and width of river is, ...
0
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0answers
13 views

Calculating the probability of electrophilic attack on terminal C atoms of butadiene using its wavefunction [on hold]

I'm studying for a test and came across this question: The highest occupied molecular orbital (HOMO) of butadiene is one of the pi orbitals and it has the coefficients: ...
0
votes
1answer
51 views

Water clock in ancient time [on hold]

A Water clock used in ancient Greek is designed as a closed vessel with a small orifice O.The time is determined according to the level of the water in the vessel. What should the shape of the vessel ...
0
votes
1answer
16 views

Equilibrium Number of Vacancies [on hold]

I have a question: If the formation energy for a vacancy in platinum is 1.62eV per vacancy, calculate the equilibrium vacancy concentration at the temperatures: 300 & 2000K. Compare the results, ...
0
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0answers
15 views

Modelling a pendulum [on hold]

I have an inverted pendulum here: http://postimg.org/image/agptuob0l/ and am just wondering how equation (2) on this page ...
0
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0answers
17 views

Photoelectric effect and work function relation

Let's consider the graph above for two metals $M_1$ and $M_2$ showing relation between photocurrent and potential. First question that I want to ask here is that how do you relate stopping ...
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1answer
54 views

Covariance of the Dirac Equation

i want to show that the following equation holds: $$ \frac{1}{8}\left[\gamma^{\mu},\omega_{\mu \nu} [\gamma^{\mu},\gamma^{\nu} ] \right] = \omega^{\mu}_{~~~\nu}\,~ \gamma^{\nu} $$ $\gamma^{\mu}$ ...
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1answer
47 views

Newton's Law problem with friction [on hold]

I'm trying to answer the following question: A force of $50~\text{N}$ acting at $37^\circ$ above the horizontal pulls a block along the floor with constant velocity. If the coefficient of ...
0
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0answers
15 views

Perpendicular Current Carrying Wires Forces?

Hi guys, I'm having trouble understanding the effect of sides BA and CD on the straight wire. With an amperian loop around the straight wire, the magnetic field on BA and CD is into the page, and ...
16
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6answers
4k views

Is it possible to shoot bullets in space or would the recoil of the gun be too strong?

I've read a few articles that say that astronauts have already brought guns in space and that shooting bullets in space is possible. But won't the recoil of the gun be too strong? Law of ...
0
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0answers
22 views

Magnetic field of cylinder equal to two current loops?

I was reading a text about the magnetic field of a uniformly magnetized cylinder when I came across this. The author states that since \begin{equation} A_{\phi}(\rho,z) = \frac{\mu_0 a M}{4\pi} ...
5
votes
3answers
122 views

What would it take to cause lightning to jump between the Moon and the Earth?

This question comes from @Floris' speculation at the end of his excellent answer about what it would take to kill everyone on the Earth with electricity. Doing all this in 1/10th of a second ...
-3
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0answers
17 views

plot of h(a function of redshift). vs angle of rotation of plane polarised light over cosmological distances [on hold]

um doing a project on cosmic optical activity,trying to explain the cosmic optical activity using U(1) chern simons term.Trying plot the data. as far as theoretical part is concerned,I've worked out ...
0
votes
1answer
35 views

How to calculate the expectation value of position vector?

$$\psi (\vec{x})=Ae^{-(1/4a^2)|\vec{x}-\vec{x}_0|^2}e^{i\vec{p}_0\cdot \vec{x}/\hbar}$$ The wave function is like this, then how is the expectation value of position vector (not position) calculated? ...
0
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1answer
36 views

Force and initial height of thrown object [on hold]

You stand at the earth's surface, and you throw a ball of mass m1 into the air perpendicular to the surface. Let g at the surface be 9.81m/s^2. You know two points (height:h1, h2 and time:t1,t2) of ...
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0answers
40 views

Equivalence of delta functions when calculating decay rate [on hold]

$\newcommand{\bs}{\boldsymbol}$ Hello, I'm currently working through the lecture notes of my Theoretical Particle Physics course, and there, we are calculating the decay rate of the following process ...
-3
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0answers
31 views

Size of upward force actin on the rocket! [on hold]

A 1500 kg rocket lifts off from the surface of the Moon by expelling exhaust from its lower end as shown. The force applied to the exhaust gas is 15 000 N downwards. Since the rocket is lifting off ...
0
votes
1answer
21 views

About environmental lapse rate [on hold]

On a spring day a middle-latitude city about latitude 40N and a temperature of 10°C has a surface (sea-level) environmental vertical soundings reveal a nearly constant lapse rate of 6.5°C per ...
3
votes
1answer
63 views

Force and lions

Alright. So me and some other people right now need an answer to this. If you have 1 trillion lions traveling at 81 kilometers (top speed of a lion) towards the Sun in a pretty dense ball. (As dense a ...
-1
votes
0answers
21 views

What is the terminal velocity of a tungsten cylinder 20ft long and 2ft wide? (if it had a more aerodynamic end) [on hold]

I read somewhere that the drag coefficient of a sphere is 0.5. so I tried calculating with that and got 4150 MPH. I don't know if 1 would be a flat end or not. However I would assume if you were ...
1
vote
1answer
65 views

How can we prove this system is in a stationary state?

I'm having trouble using the given hint to solve the problem. The problem statement is as follows: At instant $t=0$, the probability distribution of a particle under a potential $V(x)$ is ...
1
vote
2answers
138 views

$\nabla^{\mu}\nabla_{\mu}$ in general relativity [on hold]

I am trying to work out $\square=\nabla^{\mu}\nabla_{\mu}$ in the metric $ ds^{2}=-A(r)dt^{2}+B(r)^{-1}dr^{2}+r^{2}d\Omega^{2} $$ My work: when applying $\square$ to a scalar $\phi$, then $ ...
0
votes
1answer
32 views

How to solve infinite square well with exponential solution (of oscillatory type)?

Given a potential well of $V = 0$ on the interval $(0,L)$ and $V = \infty$ outside the well, I am working to solve the Time Independent Schrodinger Equation $$\dfrac{d^2}{dx^2} \psi= ...
0
votes
1answer
26 views

Final charges on Capacitors connected in a curcuit

Capacitor C1 is charged to a Potential Difference of 10V. It's capacitance is 2 microFarad. Capacitor C2 is charged to a Potential Difference of 15V. It's capacitance is 4 microFarad. Now the ...
1
vote
0answers
20 views

SR: vector field and change of reference [on hold]

If $U$ and $V$ are vector fields, then the derivative of $U$ along $V$ is the vector field $\nabla _V U$ with components $$\nabla _V U=V^b \frac{\partial U^a}{\partial x^b}.$$ I would like to verify ...
0
votes
0answers
44 views

Description of charged circle with Dirac delta function in Cartesian coordinates [on hold]

I need to describe density of charge of uniformly charged circle ($x^2+y^2=R^2$; $z=0$, total charge $Q$) with Dirac delta function in Cartesian coordinates. In cylindrical coordinates it is: $$ \rho ...
2
votes
2answers
81 views

What is the Hermitian adjoint of operator $\hat{K}\psi = \psi^*$?

For many operators, their adjoint can be expressed as a function of other known operators, for example $$\hat{T}_a^\dagger = \hat{T}_{-a} \\ \hat{p}_x^\dagger = \hat{p}_x$$ where $\hat{T}_a \psi (x) = ...
0
votes
3answers
57 views

Tension on a string

A string is attached at both extremities and put under tension $T_0$ at rest. We know that if we pull the string upwards from the middle, the tension will increase. But why is it that, admittedly, ...
1
vote
2answers
38 views

Error calculation in parallel resistances

This is the question: There are two resistors with resistance values $R_1=100\pm3$ ohm and $R_2=200\pm4$ ohm. Find the equivalent resistance of parallel combination. According to what I've ...
0
votes
1answer
66 views

How to derive this equation? [on hold]

How to derive this equation? It comes from a book named Seismic Wave Propagation in Stratified Media.
2
votes
1answer
195 views

Wave on a guitar string, differential equation

The mechanical energy of an element of the string is : $$dE(x,t) = \frac{1}{2}\left[T_0\left(\frac{\partial y}{\partial x}\right)^2 + \mu\left(\frac{\partial y}{\partial t}\right)^2\right]dx$$ Where ...
0
votes
1answer
24 views

Diffraction in Circle of light? [duplicate]

I'm working on a project that refers to optics. the question says when a laser beam is aimed to a wire ( perpendicular to the surface ), a circle of light then will be seen on a the surface. I somehow ...