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
30 views
energy and momentum problem :P [closed]
A 170 g cue ball makes a glancing blow to a stationary 170 g billiard ball. After the collision the cue ball deflects with a speed of 1.2 m/s at an angle of 30.0° from its original path. Calculate the ...
-1
votes
1answer
42 views
Electric fields problem
Why is this the case..
I would have thought it would have followed the E field?
1
vote
1answer
69 views
Two balls falling one above the other
Two balls, first with the mass $m_1$ and the second with the mass $m_2$ are falling from the heigh $h$. Suppose all the collisions are perfectly elastic and do not consider the size of the balls. $m_1 ...
0
votes
0answers
54 views
Lagrangian of three connected rods
There is free falling chain - 4 connected rods with mass m and length l:
...
2
votes
0answers
31 views
Normalizing a continuous distribution [migrated]
I work at a help/tutoring center at my university. Today a kid came in with this problem. I've only studied math and haven't drifted into physics, but he had this problem:
Let ...
-5
votes
0answers
32 views
A tank full of water has a small hole at its bottom [closed]
A tank full of water has a small hole at its bottom. If one forth of the tank is emptied in $t_1$ sec and remaining three fourth of the tank is emptied in $t_2$ sec, the ratio of $t_1/t_2$ is?
-3
votes
0answers
44 views
How much force is required to lift this car (all details/info provided)? [closed]
I have the details and info, but not the knowledge on how to determine the weight in any sensical manner.
Approximately, on or off, or exact, about how much force is need to lift this car from the ...
-2
votes
0answers
40 views
How to derive an oscillation period formula? [closed]
Given that the position function of a object flowing on a circle is $y = w-a\sin(y)$.
Why does the oscillation period $T = \int dt$ ? Why does this make sense?
-2
votes
0answers
72 views
Rotating pipe with bug [closed]
A thin mass less horizontal pipe rotates about a vertical axis with angular speed $ω$ as shown in the figure. A small bug, located at a distance $r$ from the axis, starts crawling inside the pipe at ...
-2
votes
1answer
27 views
How to take integral of a spherical function $f_{(t,r,\theta,\phi)}$? [closed]
I know that volume integral is possible for a function of $f_{(r,\theta,\phi)}$ but How to take integral of a spherical function of $r$, $\theta$, $\phi$, which depend on time too?
...
-7
votes
0answers
28 views
Mechanics Special Problem 4 [closed]
A block of mass M is pulled with a rope that exerts a force of a magnitude F, causing it to slide over horizontal ground with kinetic coefficient of friction μ (use "mu" when you input your answer). ...
0
votes
1answer
35 views
Question on static friction [closed]
This is the question, and the answer is given as 2).
Now my basic doubt is, are they asking us the direction of the total contact force on the object by the floor? Or, are they asking the direction ...
1
vote
1answer
52 views
Mechanics question (a block on top of a block)
This question is very similar to this one here.
A block of mass $m_1$ is placed on another block of mass $m_2$ lying on a smooth horizontal surface.
The coefficient of friction (static and ...
3
votes
1answer
71 views
Orthochronous Lorentz transformations are time-preserving and $SL(2,\mathbb{R})$
Let's consider the psuedosphere/hyperboloid in $\mathbb{R}^{1,2}$ given by
$$x^2+y^2-z^2=-R^2.$$
We know that the Lorentz group
$$O(1,2)=\{ A \in Mat(3,\mathbb{R}): A^tGA=G \},$$
where ...
-2
votes
0answers
16 views
What to look for in a discrete fourier transform [migrated]
I was attempting to do a discrete Fourier transform through a computer program on a list of numbers. Before doing that I decided to test it by running through a list of 1000 numbers which I created by ...
-4
votes
0answers
30 views
Please Give me the Correct Answer with Explanation. Thanks in advance [closed]
One end 'A' of a wire AB is radiated with $ \alpha $-rays and other end 'B' with $ \beta $-rays. Then:
(A) Current will flow from 'A' to 'B'
(B) Current will flow from 'B' to 'A'
(C) Current will ...
2
votes
2answers
54 views
Decomposition of this wave function in eigenfunctions
I have this wave function of a system on a central potential: $V(r)$:
$$\Phi(x,y,z)=C(x+y+z)e^{-\alpha r^2}.$$
And I'm asked a few things about probabilities. I don't have problems with that, because ...
2
votes
2answers
53 views
Are higher order mixed partial derivatives of wave function with different ordination equal?
For example, given two operators:
$$A = \frac{\partial}{\partial x}+\frac{\partial}{\partial y},$$
$$B =\frac{\partial^2}{\partial x^2}+\frac{\partial^2}{\partial y^2} + 1.$$
Deriving commutator ...
2
votes
0answers
27 views
Is there an equation that tells you more about the amplitude of an object which is in resonance?
I'm a high school senior and I have to write a paper about resonance and differential equations. I've been searching the Internet for a long time, but I haven't found an equation that is properly ...
-4
votes
0answers
29 views
Physics question based on motion in one dimension [closed]
2 trains $A$ and $B$ are moving in same direction at same track with $B$ ahead of $A$ with speed $u$ and train $A$ with speed $v$ ($v>u$). The driver of $A$ sees $B$ and starts decelerating with ...
-2
votes
2answers
50 views
Magnitude of force to keep stick in equilibrium
Problem statement
A straight and homogenous stick with mass m is pressed against a wall with the force F. The stick is horizontal perpendicular against the wall. Given that the friction between the ...
0
votes
1answer
33 views
Energy of a cylinder rolling down a path
Problem statement:
A cylinder rolls without slipping down a hill. It is released from height h. What is its speed when it come down? The cylinder mass may be completely concentrated on the radius R, ...
2
votes
0answers
50 views
Infinitesimal $SO(N)$ transformations [migrated]
An infinitesimal $SO(N)$ transformation matrix can be written :
$$R_{ij} = \delta_{ij}+\theta_{ij}+O(\theta^2)$$
Now it has to be shown that $\theta_{ij}$ is real and anti-symmetric.
I've started ...
-2
votes
1answer
23 views
Tension in parallel springs [closed]
A block of mass $200$kg is connected to a horizontal ceiling by four identical light elastic ropes, each having natural length $7$m and stiffness $180$N/m. It is also connected to the floor by a ...
1
vote
0answers
48 views
How to absorb a characteristic line in a spectrum
I have an x-ray tube. When I see the spectrum, I notice the characteristic lines of the anode. What do I have to do if I want to absorb a characteristic line?
I have thought that I can add a filter. ...
-2
votes
1answer
31 views
Elastic Spring And Energy Issue
I`m trying to write an expression ( Work & Energy ) of spring that is not loose and it has a box on it with a weight of 1Kg.
how its should be? this is what I tried to do:
$$\frac{kx^2}{2}-mg$$
...
-2
votes
0answers
26 views
Young's double slit question [closed]
An ideal Young's double slit( i.e. identical slits with negligible slit width) is illuminated with a source having (lambda)1=418.6nm & (lambda)2=421.4nm. The intensity at lambda1 is double of that ...
2
votes
1answer
37 views
Kahn-Penrose metric
the following line element defines the Kahn-Penrose metric with coordinates $(u,v,x,y)$ and constraints $u \geq 0$, $v < 0$
$$ds^2=-2dudv+(1-u)^2dx^2+(1+u)^2dy^2$$
If we restrict ourselves to ...
-1
votes
0answers
37 views
If Galileo had an electronic scale [closed]
If Galileo had an electronic scale, capable of absorbing the collision (without breaking) of 1 Kg sphere dropped from the top of Pisa tower what would had been the maximum measurement registered after ...
-5
votes
1answer
23 views
charge placed on a capacitor [closed]
a parallel plate capacitor has plate area of 0.0025 m^2 and distance between the plate of 2.0 mm. Determine the maximum charge that can be place on the capacitor if air is the dielectric substance
-1
votes
1answer
57 views
Problem from Sakurai about a delta-function potential [closed]
Can you help me with this problem from Sakurai:
A particle of mass m in one dimension is bound to a fixed center by an attractive delta-function potential:
$$V(x) ~= ~-a\delta(x) , \qquad ...
0
votes
0answers
37 views
Plane area as a vector?
Which according to you is the most incorrect statement?:
1)Plane area can be treated as a vector only if it is very small.
2)Plane area can be added as vector, i.e. using triangle or parallelogram ...
-7
votes
1answer
41 views
Time it takes 1 gallon of water to flow out of 2" pipe? [closed]
A 2"diameter pipe that is 10' in length with a vertical orientation. The pipe is filled to the top with water. The pipe is open to atmosphere at the top(no additional pressure other then gravity). ...
-1
votes
0answers
19 views
Writing right and left polarized waves in terms of parallel field components
How can I write:
in terms of:
(or vice verse - I can't see how they relate).
I don't see how you can right and left polarized waves in terms of parallel E and B components?
-3
votes
0answers
31 views
Determination of the capacitance of a capacitor [closed]
This is the physics taught in here in Lebanon , by the old french system it may look somehow unfamiliar to some, can some solve it ?
Circuit : Low Frequency Generator,Resistor,Capacitor (in series)
...
0
votes
1answer
26 views
Power radiated by a star, black body model
let's say I want to model a star of radius $R$ at a distance $r$ from the Earth. I need to show that the apparent luminosity for frequency $\nu$ is equal to
$$\ell(\nu)=\frac{2\pi h}{c^2}\left( ...
-3
votes
2answers
151 views
Newton Laws of Motion + Effective spring Constant [closed]
!
Can someone please help me in solving this question:
What is the effective spring constant for the system of the two springs, perfect pulley, and string shown on the left for it to be modeled ...
-1
votes
0answers
32 views
Calculating Apparent Depth at any angle: am I doing it right?
just wanted to check my understanding was right as scientific & mathematical equation notation is all a bit new to me - familiar as I am with equations in a programming context. I need to be able ...
3
votes
1answer
61 views
Integrable equations of motion
Suppose that a force acting on a particle is factorable into one of the following forms:
...
4
votes
2answers
85 views
Is there a general form for heat capacity?
Can you derive a general form (not keeping either volume or pressure constant) for heat capacity from the first law of thermodynamics? Do you have to make any assumptions to do so?
It sounds trival, ...
-1
votes
0answers
32 views
Possible outcomes of measurement on a state
I having some trouble understand a question I'm handed. I doesn't seem to be difficult, I think, but I'm having some trouble understanding what I actually have to do.
I have the following variable ...
0
votes
1answer
52 views
Showing Dirac Hamiltonian is hermitian
I'm trying to show that $H_D = -i\boldsymbol{\alpha}.\nabla+\beta m$ is hermitian.
Its given that
$$
\gamma^{0\dagger}=\gamma^0
$$
$$
\boldsymbol\gamma^\dagger=-\boldsymbol\gamma
$$
What i've done ...
3
votes
2answers
99 views
Do I think or listen - physics talks [closed]
I am just a student, still I have already listened to a few talks on physics. In my study program everyone has to give a talk of about 45 minutes what he did in his about 1-2 month reach project ...
1
vote
0answers
27 views
Superradiance of electromagnetic waves
I have to do a calculation (problem 5 of chapter 12 in Wald) verifying the super-radiance of electromagnetic waves incident on Kerr black holes and have a few preliminary questions.
As background: ...
1
vote
1answer
61 views
Pressure in Bernoulli's equation
!
I've been reading an introductory physics textbook. It has a chapter on fluids which I'm finding quite confusing. Specifically, I don't understand the meaning of the pressure terms $P_0$ and $P_1$ ...
-5
votes
0answers
41 views
Jumping into the water from certain [closed]
a person who, starting from rest at the top of a cliff, swings down at the end of a rope, releases it, and falls into the water below. There are two paths by which the person can enter the water. ...
2
votes
0answers
46 views
Current to cancel Earth's magnetic field
I'm making a lab report where I've used a Helmholtz coil and a magnet to find Earth's magnetic field intensity in the area by relating the frequency of oscillation of the magnet when a certain current ...
2
votes
1answer
36 views
Probability for harmonic oscillator outside the classical region
I'm having some trouble finding an expression for the probability to find the particle outside the classical area in the harmonic oscillator.
I have a wavefunction defined as:
$\psi \left( x,\,t ...
-2
votes
0answers
30 views
Angles of Two Rotating Beams Connected by a Rod [closed]
Two beams with radii $R_s$ and $R_m$ are hinged a fixed distance $d$ apart. They are connected at their tips by a rod of fixed length $x$. If the beams start out parallel to each other and ...
1
vote
1answer
40 views
Average force and pressure in a 3D box due to quantum non-interacting particles
A gas of non-interacting quantum particles occupies a box with lengths $L_1, L_2, L_3$. Calculate its energy and thus the average force and pressure exerted by the gas on the walls of the box.
I have ...
