Tagged Questions

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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0
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0answers
7 views

Separation distance of bright fringes in double slit experiment

so I'm working on homework problem that seems like it should be pretty straight forward but the computer won't accept my answer. The question is below. A double slit aperture with slit separation ...
0
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1answer
21 views

tangential acceleration and angular acceleration

$$r= 2 \text{ m}$$ $$a_{\text{tangential}}=\frac{\pi}{4} \text{ m/s}^2$$ for half a turn What is the angular velocity from rest of the circular path? $$a_{\text{angular}} = ...
1
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1answer
29 views

Energy in harmonic oscillator

The expectation value of the potential energy is exactly half the total according to Griffiths. Is that case always true for quantum harmonic oscillator? Is that the case also for classical harmonic ...
1
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0answers
12 views

Heat Transfer and Thermal Energy

Some hot water radiators have a single pipe connected to them. The steam comes to the radiator and the water leaves in the same pipe. The steam and the water are both at a temperature of 100°C. Where ...
2
votes
0answers
28 views

1D Finite potential well: solutions with $\sinh$ and $\cosh$?

So I am studying the (one dimensional) quantum mechanical finite potential well defined by: $$ V(x) = \cases{0, &|x|>a\cr -V_0, &|x|<a} $$ where $V_0>0$ is a real number. I know ...
0
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1answer
49 views

Difference between a hydrogen ion and a proton

I've run into a bit of a problem on this weeks coursework. A proton and an electron initially at rest combine to form hydrogen. Find the wavelength of the emitted photon? So, as far as I can ...
1
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0answers
25 views

Finding conserved quantities from Hamiltonian when Symmetry is not evident

A particle is moving in 3D space, under a potential $$V = -\frac{\alpha}{r}-\frac{\vec{r} \cdot \vec{\mu}}{r^3 } $$ where $\vec{\mu}$ is some constant vector. I need to show there are three ...
-2
votes
2answers
25 views

What does $\tau$ = $\Delta E_{c}$ mean? [on hold]

What does $\tau$ = $\Delta E_c$ mean? Can anyone help? I'm finding it difficult to find on the internet.
0
votes
1answer
39 views

Pushing over a block [on hold]

Consider a rectangular block of mass $m$ and uniform density resting on a frictionless surface. The height is $h$, the width $w$, the length $l$. Consider one of the faces with dimmensions $l$ by $h$. ...
0
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2answers
34 views

Forces and acceleration on rotating objects? [on hold]

Suppose you have an object undergoing uniform circular motion, with force vector pointing towards the center and another force vector tangential. Can it be said that the net force pointing in the ...
1
vote
1answer
87 views

Deriving a Useful Solution of the Schrödinger Equation [on hold]

How does one derive the fact that $$\psi(t,x) = (\tfrac{2 \pi \hbar t}{m})^{-d/2}\int_{\mathbb{R}^d} e^{im\tfrac{(x-y)^2}{2\hbar t}}\psi_0(y)dy$$ is a solution of the time-dependent Schrödinger ...
-1
votes
0answers
25 views

Stuck on Snell's Law [on hold]

I'm currently studying triple science at GCSE level and we have just learned Snell's Law. I have been given homework on the topic, but I'm a little bit confused as to when I used sin, inverse sin, ...
3
votes
3answers
270 views

Should a Gaussian Curve Always Be Drawn Symmetrically?

This question is more about the appearance of a curve that comes up while I am analysing my data rather than an actual physics question, but I think it's relevant. I have analysed some data from an ...
-1
votes
1answer
24 views

Find the impulse momentum [on hold]

A boy of weight 40 kg stands on a board of weight 60 kg. The board is on ice (friction force =0): Find the velocity of the movement of the boy and the board when he moves from one side to another.
0
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0answers
16 views

Convert this to a Hamiltonian system and find Hamiltonian [on hold]

I tried solving this by using the conjugate momentum and position formulae: but could not get the answer. EDIT: I have used the same procedure as mentioned in this Phys.SE answer but the ...
0
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0answers
42 views

Help with my schoolwork [on hold]

I have to do project about Newton's Movement Laws, and I decided to write about the situations, where do NML not work. For example, why does photon have force and momentum, when it has 0 mass. It's ...
1
vote
1answer
48 views

By what force does a man attract Earth? [on hold]

By what force does a man attract Earth? a) 800N b) 80N c) he doesn't attract it By putting some values into the formula for gravitation force I get about 785N. Is it (a) then?
-2
votes
0answers
8 views

Solving for initial velocity required to launch a projectile to a given destination at a same height formula [on hold]

with the premise that gravity (gravity is 10m/s) is the only force acting on it after initial launch (no air friction) the angle is 30 deg and the destination is 40 meters
0
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0answers
21 views

Ames Room, how to construct properly?

I have been assigned to create an Ame's Room for a physics project. However, the teacher told us very little about it, and wanted us to figure it out through trial and error. Today I spend 6 ...
0
votes
0answers
9 views

Transistor Series Regulator [migrated]

I am in the 6th week in Navy school and we are on voltage regulators or circuits that have components that maintain a constant voltage output. I need an explanation on how to work out this problem ...
1
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2answers
178 views

Triple integral $\iiint_{\mathbb{R}^3} d^{3}q ~\delta^{3}(\vec{q})\frac{(\vec{p}\cdot\vec{q})^2}{q^{2}} $ involving Dirac Delta function

I am trying find $$\iiint_{\mathbb{R}^3} d^{3}q ~\delta^{3}(\vec{q})\frac{(\vec{p}\cdot\vec{q})^2}{q^{2}},$$ where $\vec{p}$ is some fixed vector. The answer should be $\frac{p^2}{3}$. Below is ...
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0answers
35 views

Allowed Values of Angular Momentum for a Rotating Mass

I am attempting to calculate all possible values of angular momentum, $L_z$, which can be found by making a measurement on the following system: A small mass, $M$, is attached to the end of a rigid, ...
1
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1answer
19 views

Calculating energy density in the early Universe

I've been told to calculate the energy density in the early Universe. It states that it is completely dominated by neutrinos (3 species), photons, electrons, and positrons. Now, I've found an ...
0
votes
1answer
25 views

Finding acceleration only with known acceleration distance, final velocity, and mass for Newton's Third Law [on hold]

So I have this problem that I am trying to figure out. I need to find the acceleration of a 4 kg object, that is accelerated through a distance of 1 m to the left to a final velocity of 6 m/s. This ...
0
votes
2answers
21 views

How to determine the difference between object distance and image distance? [on hold]

How do we derrive the last equation? Whatever I tried it didn't work... Oh man I just saw, that all the did is write $b=3m-g$, how was is it possible for me to miss it...
-1
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0answers
42 views

how to prove the following equations? [on hold]

Equations in this image include some confusing steps for me, I tried but no results came out. please if some one can solve it I'll be very thankful.
0
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0answers
50 views

Writing this in a neater more compact way [on hold]

If one has $$ (\frac{d\omega^2}{dx^1} - \frac{d\omega^1}{dx^2}) (\theta^1 \wedge \theta ^2) +(\frac{d\omega^3}{dx^2} - \frac{d\omega^2}{dx^3}) (\theta^2 \wedge \theta ^3) +(\frac{d\omega^1}{dx^3} - ...
1
vote
2answers
127 views

Why is $\nabla\cdot(\hat{\bf r}/r^2)$ giving 0 as answer? [on hold]

While I was reading I encountered the statement $\nabla\cdot(\hat{\bf r}/r^2)$ (r cap divided by $r$ square) is 0. Can anyone explain proof of the statement why is it giving 0?
-1
votes
0answers
21 views

Find angular speed? [on hold]

The propeller blades of an airplane are 4.0 m long. The plane is getting ready for takeoff, and the propeller starts turning from rest at a constant angular acceleration. The propeller blades go ...
0
votes
0answers
41 views

Geometric optics question

This question appeared on this site Q17: here A concave mirror is broken into two parts and these parts are separated by a distance if 1 cm. The focal length of the mirror is 10 cm. Find the ...
0
votes
2answers
14 views

What happens to the electric charge of a rod and a cloth if the rod is rubbed with a cloth? [on hold]

We have a rod and we rub it with a cloth. Will the rod have a positive charge and the cloth have a negative charge? Will both the rod & cloth have a positive charge? Both rod & cloth have a ...
0
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0answers
15 views

Antiunitary operator, momentum operator [on hold]

Assuming the time-reversal operator $T$ $T|x>=|x>$ Now I want to calculate $TpT^{-1}$ So, $TpT{-1}|x>=Tp|x>=\int\int T|x'><x'|p|p'><p'|x>=\int\int ...
0
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0answers
26 views

Metallic coin over wooden block in glass of water

So there is some water inside a container; the height of water inside the container is $l$. I placed a wooden block on the water and it's floating to some height $x$, on top of the block is a metallic ...
1
vote
1answer
54 views

Eigenvalues of hamiltonian [on hold]

Q: THe hamiltonian which describes the motion of a particle in an one dimensional potential V(x) is $H_0=\frac{p^2}{2m}+V(x)$ , where $p=-i\hbar \frac{d}{dx}$ is the momentum operator. $E_n^0$ , ...
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0answers
27 views

Uniqueness of the Einstein tensor

This is related with an exercise 17.4-a in MTW Here what i want to show is the Einstein tensor $G_{\alpha\beta} = R_{\alpha\beta} - \frac{1}{2} R g_{\alpha \beta}$ is the only second-rank, symmetric ...
0
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0answers
22 views

Constructable components on metric and its derivatives [on hold]

This is exercise 17.2 in MTW Show that there exists no tensor with components constructable from the ten metric coefficient $g_{\alpha\beta}$ and their 40 first derivatives, ...
0
votes
1answer
26 views

Polarisation vectors in the quantization of electromagnetic field [on hold]

How can we prove $ \sum^{3}_{\lambda =0} \sum^{3}_{\lambda^{'}=0} \epsilon^{\lambda}_{\mu}(k)\epsilon^{*\lambda^{'}}_{\nu}(k) g^{\lambda \lambda^{'}} = g_{\mu\nu}$ where the $\epsilon$ are the ...
0
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0answers
10 views

Introducing a conductor in a capacitor [on hold]

1) A capacitor is taken and a Conductor (Not a dielectric) is inserted in between the plates (made of a different material other than the conductor) like: What will be the new capacitance, How much ...
1
vote
1answer
15 views

Identification of massless, chargeless $x$ in a nuclear reaction

On Friday, we had our Physics test. We (the tenth grade students) have the basic introduction to Radioactivity and a few nuclear reactions in our syllabus. In the test, the following question was ...
-2
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0answers
13 views

Diffusion Equation [on hold]

Please give me some guidance on my following assignment of Simulations in fluid flow: Thank you. Solve the following differential equation for transport of f(x,y,z,t) by MS Excel ∂f/∂t+Ux ∂f/∂x+Uy ...
0
votes
0answers
15 views

How to simplify logic circuit? [on hold]

Only the AND, OR, NOT gates are there in my course and I know only how to write results including only a single of these, but my course has no mention of solving these: I just wrote ...
1
vote
0answers
144 views
+250

Horrifying electron gas model

I am given the Hamiltonian, in an exercise called plasmons, and where $\langle, \rangle $ denotes the expectation value. $$ H = \sum_{k} \varepsilon_k a_k^{\dagger} a_k + \sum_{k_1,k_2,q} V_q ...
1
vote
1answer
30 views

How to determine velocity of two objects after they collide? [on hold]

Let's say an object of mass 1 kg is moving 10 m/s. A second object of mass $m_2$ is at rest. When the two objects collide, they stick together and move 8 m/s. what is $m_2$? I understand how to solve ...
-1
votes
0answers
14 views

How to relate the height from which a object can fall with the young modulus of that object? [on hold]

How to relate the height from which a object can fall without breaking with the Young modulus of that object?
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0answers
21 views
1
vote
0answers
16 views

Suspended mass in motion free-body diagram [on hold]

A 20kg mass is held by two ropes which span 90 from each other. The mass is being accelerated at 1m/s^2 to the right. Draw a free body diagram for the mass and find the numerical values for each ...
0
votes
0answers
19 views

Determine coefficients so that $f(x,y)$ is a conserved quantity [migrated]

Given the function $f(x,y) = ax^2y + by + ct^2 $ with $x(t)=2t$ and $y(t)=3t^2$ I shall determine the coefficients a,b,c so that $f(x,y)$ is a conserved quantity. My approach is $$\frac{df}{dt} = ...
0
votes
0answers
62 views

Computation of spin connection 1-form [on hold]

If stationary metric is given by $$ds^2 = e^{2U}(dt+\omega_idx^i)^2 - e^{-2U}dx^2$$ and I want to try to solve for this. After doing the effort to find the metric and its inverse, I used the tetrad ...
0
votes
1answer
34 views

Deduce the 3 dimensional Anti de Sitter space from the 4 dimensional case [on hold]

From $$AdS^4=\big\{(u,w,x,y,z) \in \mathbb{R} | -u²-w² +x² + y² + z²=-1 \big\}$$ parametrized by $$f(t,\rho, \theta, \phi) = (\sin t \cosh \rho, \cos t \cosh \rho, \sinh \rho \cos \theta, \sinh \rho ...
0
votes
1answer
63 views

Uncertainty Principle and single-slit diffraction [on hold]

A beam of 50eV electrons travel in the x direction towards a slit of width 6 micro metres which is parallel to the y direction. The diffraction pattern is observed on a screen 2 metres away. Use ...