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.
-3
votes
0answers
54 views
Raising/Lowering Operator [closed]
The question asks; For a harmonic oscillator,
$$
\langle2|a_{-}\,a_{+}^{3}|0\rangle
$$
which equals...
And there are numerous multiple choice answers. I calculated $$2\sqrt3$$ but the answer sheet ...
-1
votes
0answers
19 views
Renewable Energy - biomass [closed]
A timber mill produces I tonne of hog fuel, with a moisture content of 45%, daily from its saw-milling operations. What is the maximum output power that can be produced from a steam turbine driven ...
-3
votes
0answers
31 views
Projectile Motion and hexagon [closed]
A projectile passes through four vertices of a regular hexagon of side "a". Find its horizontal range.
Now the problem is to find the horizontal range, and the time of flight. Can you please help?
-4
votes
0answers
20 views
Qual practice problems [closed]
I was working through the problems at:
http://zippy.physics.niu.edu/PhDexam/EM_ALL.pdf
but there are a good number I am not sure how to approach. Would there be solutions available for these ...
-3
votes
0answers
32 views
Harmonic oscillator problem [closed]
A force $\displaystyle F=F_0\sin\omega_0t$ is applied to a harmonic oscillator.
Initial conditions are $x=0, v=0$ at $t=0$
$i)$ Find $x(t)$
$ii)$ If the spring has a breaking point at $5F_0$ Find ...
0
votes
0answers
28 views
Magnetic deflection of electron beam [closed]
This question is from the Berkeley Physics Course Volume 1, for the record.
"A beam of electrons of energy W enters a region of transverse uniform magnetic field of strength B. (Neglect fringe ...
-1
votes
1answer
41 views
Understanding centripetal force vs frictional force diagrams?
I have an actual physics problem and also a conceptual question to go with it. From some test prep I was presented with this straight-forward question:
What is the minimum radius that a cyclist can ...
0
votes
1answer
34 views
Formation on image on screen?
When we first learn elementary geometrical optics, the first thing taught to us is the two broad divisions of the type of reflection.-Regular and Irregular or Diffused.
The difference in cause for ...
-3
votes
0answers
31 views
Block over block Problem [closed]
There are two blocks one over the other , both on ground , masses are 2 kg for top one and 5 kg for bottom one , coefficient of friction between both is 0.8 and between lower one and ground is 0.2 . ...
1
vote
1answer
58 views
Finding the Basis vectors of a Killing field vector space
I have solved the Killing vector equations for a 2-sphere and got the following answer. $A,B,C$ are three integration constants as expected.
$$\xi_{\theta}=A \sin{\phi}+B\cos{\phi}$$
...
1
vote
1answer
65 views
Plot of gauge coupling unification [closed]
About the result of plotting running of 3 coupling constant, we think that we should get the correct one(MSSM).
But we get discontinuity at $ M_{susy}$.
If there something wrong in our formulae?
If ...
-1
votes
1answer
60 views
Solving differential Equation for the Two-Body Problem
So, I'm following the derivation in D. Morin, Introduction to Classical Mechanics, of the equations for a two-body system. I understand all of it, aside from this one step.
When he's talking about ...
0
votes
1answer
70 views
Expectation value of momentum
I'm having a problem with an expectation value that doesn't seem to add up for me.
What I know is, that $\psi(\vec{r})$ is a wavefunction for a particle in three dimensions. The Hamiltonian is given ...
-1
votes
1answer
36 views
Dynamic equation
I'm asked to give the dynamic equations of a charged particle moving on a potential, under relativistic considerations, basically $dp/dt$, with $p$ the 4-momentum vector. The question for the three ...
0
votes
1answer
76 views
Proper time of circular motion under Schwarzschild metric
I'm trying to calculate the proper time of a massive particle circulating Schwarzschild black hole, using EL equation of the following Lagrangian:
...
0
votes
1answer
38 views
Deriving work done on a solid
For a homework problem, I've been asked to show that the work done by increasing pressure isothermally on a solid of mass m is: $$W \approx -\frac{m\bar{\kappa}}{2\bar{\rho}}(P_f^2 - P_i^2)$$
where ...
2
votes
1answer
50 views
From Euler-Lagrange equation to non affine geodesic equation
I have some problems to demonstrate the non affine geodesic equation from Euler-Lagrange's equations. I start defining the Lagrangian $L=\sqrt f$, but then I'm not able to find the Christoffel ...
1
vote
1answer
46 views
Proving Simple Harmonic Motion (direction of acceleration)
A particle of mass $m=0.5kg$, is attached to a spring of natural length $l=0.6m$ and modulus of elasticity $\lambda=60N$, and the setup is on a horizontal smooth table. The other end of the spring is ...
-1
votes
0answers
35 views
Quantum mechanics, harmonic oscillator [closed]
A particle of mass m moves in a harmonic oscillator potential. Theparticle is in the first excited state.
Calculate < x > for this particle.
Calculate $<p^2>$ for this particle.
At which ...
5
votes
1answer
90 views
Aharonov-Bohm Effect in Torus
I had a very brief introduction to the Aharonov-Bohm effect in class. The lecturer introduced the notion that $H(\Phi=\Phi_0)$ and $H(\Phi=0)$ gives identical energy spectrum and that the Hamiltonians ...
-2
votes
0answers
44 views
Capacitors connected [closed]
Two capacitors of capacitances 3 $\mu{F}$ and 6 $\mu{F}$ are charged to a potential of 12V each.
They are now connected to each other, with the positive plate of each joined to negative plate of the ...
-5
votes
1answer
91 views
How to derive the Time Dilation formula given: [closed]
Since I do not have 10 reputation I will fit this all in one image:
If you have any questions please dont hesitate to ask.
EDIT: http://img16.imageshack.us/img16/8604/myquestion2.png
-6
votes
0answers
62 views
solid state physics [closed]
Show that the expression for the average energy of a system can be given by the relation $E=\dfrac{KT2d\log z}{dt}$ where Z-partition function for classical one dimensional system and is given by z= ...
-3
votes
0answers
54 views
Finding equivalent capacitance between points in a cubic arrangement of capacitors [closed]
Each of the edge of a cube is containing a capacitor of capacitance 'C'. Find the equivalent capacitance between:
1 and 7
1 and 4
1 and 8
I am done with the first part to ...
-4
votes
0answers
41 views
solid state physics [closed]
One gram molecule of a certain polar substance is dissolved in to $1000 \ cm^3$ of a non polar liquid.The liquid itself has a dielectric constant of $3.0$ at 27 degrees. whereas the solution has a ...
0
votes
0answers
70 views
finding minimum electrostatic energy [closed]
There are 2 small metal balls of radius $r_1$ and $r_2$ which are kept at very large distance. What should the ratio of charges on them be for the electrostatic energy to be minimum?
In this problem, ...
0
votes
0answers
24 views
How can I get the focal length from the given information? [closed]
A man looks at a tree of height 20m a distance of 300m away. The reduced model of the eyes assumes that the cornea has a radius of curvature of 7.7mm, the eye is composed of the material with a ...
5
votes
1answer
80 views
How to derive the velocity in the double ball drop problem?
The double ball drop problem is as follows:
A ball of mass $m$ is placed on top of a ball of mass $M$ (where $m < M$), and the balls are dropped simultaneously from some height $h$. When the ...
-4
votes
1answer
30 views
From the top of a 400 m high rock by the sea, a ball is shot out in the horizontal direction. The ball speed is 100 m / s [closed]
From the top of a $400 m$ high rock by the sea, a ball is shot out in the horizontal direction. The ball speed is $100 m / s.$
a) After how much time the ball hits the water?
b) At what rate does ...
-2
votes
0answers
35 views
How large a force is needed for a wooden block to tip over? [closed]
I just need the formula. Tried.. Force * perpendicular distance = force * [Perpendicular distance from the line of action of the force to the axis of rotation], but the answer still is not the same ...
-1
votes
0answers
37 views
Reference Request: Mantle Cloaking, Invisibility and Metascreen [closed]
Reference Request: Mantle Cloaking, invisibility and Metascreen.
I'm really interested in Mantle Cloaking but I've difficulties in finding some basic references in order to study foundamental ...
1
vote
0answers
22 views
Calculate the acceleration of the trailing muon bunch
Two separate suitably short but intense bunches of muons, "A" and "B", are both supposed to be constantly accelerating (in an otherwise sufficiently flat region) with constant proper acceleration ...
2
votes
1answer
44 views
How are excess charges distributed over non-spherical conductors?
My textbook gives the following explanation on how excess charges are spread over conductors:
The excess charge on an isolated conductor moves entirely to the
conductor's surface. However, ...
0
votes
2answers
54 views
How does symmetry allow a rapid determination of the current between $A$ and $B$?
The following was originally given to me as a homework question at
my physics 2 course:
Consider the following circuit
The difference of potentials between the point $V_{1}$and the ...
0
votes
0answers
32 views
Confusion in connected pulleys problem
I'm having some troubles in understanding why my reasoning doesn't work in the following problem:
Problem Two pulleys of mass $m_1$,$m_2$ and radius $r_1,r_2$ are connected by a belt (like chain ...
0
votes
1answer
54 views
Expectation value of position in infinite square well
I'm looking for some help to a question.
I'm working in the infinite square well, and I have the wavefunction:
$$\psi(x,t=0)=A\left( i\sqrt{2}\phi_{1}+\sqrt{3}\phi_{2} \right).$$
For every time t, ...
2
votes
1answer
97 views
How do I find the energy of this Hamiltonian?
So, I have a (confusing) Hamiltonian:
$$H = \int \mathrm{d}k\,\omega_{k} a^{\dagger}\bigl(\vec{k}\bigr)a\bigl(\vec{k}\bigr)$$
where $\omega_{k} = \sqrt{k^{2} + m^{2}}$ and the measure is ...
-10
votes
1answer
42 views
Chapter 35-Electricity and Magnetism [closed]
A light bulb connected to a 3.0-V battery draws 1.2 A of current. Calculate the resistance of the bulb.
0
votes
1answer
34 views
Calculating torque with gears and wheel-axles
For my homework in engineering, I was given a question like this: There is an axle attached to a gear, which is meshed with another gear, which has an axle attached to it. I am given the diameter of ...
0
votes
0answers
51 views
heat conductivity experiment [closed]
We did an experiment at University which I feel very confused about:
The image should explain it well. One end of a metal bar insulated in a cover is left in touch with a $160\,\mathrm{W}$ heat ...
0
votes
0answers
44 views
First-order pertubation theory
I'm having some trouble figuring this out, so I was hoping someone could help.
I need to show that the first-order pertubation of the ground state energy is not changed by the pertubation $H'$, given ...
1
vote
2answers
47 views
Photon gas kinetic theory
Suppose a black body as an enclosure of volume $V$ with a hole of section $A$. In the interior there is a photon gas, whose energy density $u$ is, at temperature $T$.
$$ u=cT^4$$
How can I show that ...
-1
votes
1answer
24 views
Averaging energy density
Let we define energy density by,
$$E= a^2 \cos2 t +b^2 \sin2 t+ c^2 \cos 3t$$
where, $E=$ total energy, $a,b,c =$constants, and $t$ is the time.
I'm confused from someone's statement that `
There ...
-4
votes
0answers
91 views
Problem in understanding quantum physics [closed]
Is Heisenberg Uncertainty Principle (HUP) only Uncertainty in measuring the position-velocity? If it is so, then how we explain quantum fluctuations, Hawking radiation and so on. Please relate how ...
-4
votes
0answers
29 views
Find amount of force to move a 18 kg mass 0.1 seconds [closed]
Force is coming from two pistons pushing at 45 degrees applied to two adjacent corners of a square (0.6 m x 0.6 m) rigid plane. Mass of the plane is 18 kg. Piston stroke is 20 cm, piston bore is 40 ...
5
votes
1answer
149 views
Magnetic force doesn't do work and therefore can't change the KE of a particle?
I am having a real hard time understanding the principles behind a question I've come across during test prep. Here is the question:
Q: A proton and an electron are traveling in the uniform ...
0
votes
1answer
41 views
Total current of two sources in series? [closed]
Here is a question that a friend asked me. He had to an experiment in school and do some calculations afterwards. Those calculations require maximal current that the DC source can produce. He has ...
0
votes
1answer
66 views
Vectors on Different Coordinate Systems? [closed]
Consider the product of vectors coordinated relative to a given coordinate frame, defined by
$$\vec{a}\square\vec{b}=((a_{1},b_{1})\square(a_{2},b_{2})):=(a_{1}b_{1},a_{2}b_{2})$$
Explain why ...
0
votes
1answer
47 views
Electromagnetic Tensor in Cylindrical Coordinates
I understand that the Electromagnetic Tensor is given by
$$F^{\mu\nu}\mapsto\begin{pmatrix}0 & -E_{x} & -E_{y} & -E_{z}\\
E_{x} & 0 & -B_{z} & B_{y}\\
E_{y} & B_{z} & ...
-1
votes
1answer
35 views
Vectors and motion in a plane [closed]
A particle travels with speed $50 m/s$ from the point $(3,-7)$ in the
direction $7i-24j$ . Find its positional vector after 3 seconds.
My approach:
It has travelled a distance of 150m in the ...
