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.

learn more… | top users | synonyms (1)

2
votes
1answer
19 views

Pushing a crate on a friction floor

A man is pushing a crate at a constant velocity. there is a friction between the floor and the crate of $$\mu =0.41.$$ The pushing force is directed downward at an angle $\theta $ below the ...
1
vote
1answer
63 views

Difficulty with the usage of Cauchy's integral formula in Griffiths QM book

On page 410 of Griffiths QM 2nd Ed. book, he begins an analysis to evaluate the integral: $$\frac{1}{2i}\int_{-\infty}^\infty \frac{s \sin{(sr)}}{(s-k)(s+k)}\mathrm{d}s.$$ To exploit Cauchy's formula, ...
0
votes
1answer
69 views

Doubt in a certain equation of a research paper [on hold]

In the following research paper (link provided) , I am not able to figure out how do we get the equation (7) . Please help me out. Also , please recommend the necessary pre requisite text to ...
0
votes
1answer
26 views

Expected value $<\hat{x}>$ of: $\Phi(x,t)=Ne^{-a[(Mx^2/\hbar)+it]}$ is infinite, why?

The problem says: A particle of mass $M$ is described by the wave function: $$\Phi(x,t)=Ne^{-a[(Mx^2/\hbar)+it]}$$ where a is a positive constant. Asked to determine such things as the ...
0
votes
0answers
4 views

How to calculate the electrostatic force applied on an object that is along the axis of a charged tube's surface?

Let's say there is a charged tube(a cylinder with no top and bottom) with radius r and length l, charge q1 which also made out of insulating material. And also if there is an object with charge q2 ...
1
vote
0answers
17 views

Very short physics question (electromagnetic field): Just draw the figure of the problem? [on hold]

Can you please draw me the figure of the problem? I dont want the solution,just the figure? A straight, stiff, horizontal wire of length 25 cm and mass 50 g is connected to a source of emf by light, ...
0
votes
0answers
43 views

Molecular simulation - Lennard-Jones potential [on hold]

For 2 atoms separated by a distance $r$, the potential function is given by $$u(r) = 4\epsilon [ (\sigma/r)^12 - (\sigma/r)^6]$$ (Lennard-Jones potential). Give the equation that define how pressure ...
0
votes
0answers
24 views

calculating electrostatic force [on hold]

I am trying to answer this question: Calculate the electrostatic force on a metal ion carrying a charge of $3.2$x$10^-$$^1$$^ 9\ \text{C}$, and which is in an ionic solution between two parallel ...
1
vote
0answers
20 views

How to calculate the electrostatic force applied on an object that is along the axis of a charged tube?

Let's say there is a charged tube(a cylinder with no top and bottom) with radius r and length l, charge q1 which also made out of insulating material. And also if there is an object with charge q2 ...
0
votes
0answers
56 views

Integrating a Dirac delta function with the argument dependent of a parameter [migrated]

How can I handle the integral $$ \int_{t_1}^{t_2} \delta(D - x(t)) dt, $$ with $D$ a constant. I want to do a change of variables to perform the integral over $x$ but I am not sure how to proceed.
0
votes
0answers
31 views

Complex Conjugate of Wave Function's Derivative

I am reading Griffiths QM textbook and I got confused by the following identity: How to prove from $$\frac{\partial \Psi}{\partial t} = \frac{i\hbar}{2m} \frac{\partial^2 \Psi}{\partial x^2} - ...
-6
votes
1answer
46 views

calculating distance traveled - I do not have anyone to teach me this [on hold]

Find the resultant displacement of a bear searching for berries on the mountain. The bear heads 55.0º north of west for 15.0 m; then it turns and heads to the west for another 7.00 m.
1
vote
1answer
17 views

Given the spring constant & maximum kinetic energy; length of spring extension? [on hold]

I need to understand the following question before i right my exam tomorrow. A body attached to a spring with spring constant 100 N/m executes simple harmonic motion. The maximum kinetiv energy of ...
0
votes
0answers
26 views

Calculating height and evaluating the vicinity of a peak in a multiplicity function for a two-state paramagnet

I have to calculate the height and width of the multiplicity function for a two-state paramagnet. I'm supposed to do this analogously to the method in the text book, which I will try to outline below. ...
0
votes
1answer
31 views

Moment of inertia of half a thin disk around oo' axis [on hold]

How do I calculate the moment of inertia of this object around the oo' axis. I know how to calculate a whole disk (with or without the hole) around: 1. the center axis 2. the oo' axis (using the ...
1
vote
1answer
43 views

How can I derive the Hamiltonian of simple harmonic oscillator from this Lagrangian?

I'm working through Leonard Susskind's Theoretical Minimum: Classical Mechanics and I can't seem to understand how the Hamiltonian of a simple harmonic oscillator is derived from the following ...
0
votes
0answers
34 views

Given the Gas, Temperature and Pressure find Volume? [on hold]

Give the specific volume of carbon dioxide at -20 C for 2000 kPa and for 1400 kPa. I am getting ready for Thermodynamics class so I've been reading the textbook and doing some questions, I can ...
-4
votes
0answers
24 views

About one dimensional motion [on hold]

A particle moves in a straight line and its position x at time t is given by x^2 = 2+t. Its acceleration is given by -2/x^3 -1/4x^3 -1/4x^2 1/x^2
-2
votes
0answers
28 views

Wondering what textbook is this problem from? [on hold]

Wondering from what textbook is this problem for?
0
votes
1answer
53 views

Massive ropes and tension

Consider the diagram bellow, a massive string hanging in equilibrium My question is this: Can we take any 2 random point on the rope, say A and B and then use $\sum F=0$ on the rope between them: ...
-3
votes
0answers
24 views

Find out angle of a projectile [on hold]

For a projectile launched from a point on horizontal ground, the speed when it is at the greatest height is 25−−√ times the speed when it is at half of its greatest height. Determine the angle of ...
0
votes
1answer
22 views

What is the work done below proportional to? [on hold]

A raindrop falls from a certain height to the ground, with a terminal velocity u. The viscous force is F = 6*3.14*n*r*v, where n is the coefficient of viscosity, r is the radius of the raindrop, and v ...
3
votes
3answers
55 views

Ampere's law and external currents

In Ampere's law the current outside the curve taken is not included in the expression. Does this mean that only the currents crossing the area bounded by the curve taken contribute to the magnetic ...
1
vote
0answers
24 views

Similarity in two events from Dynamics point of view [on hold]

What is similar from dynamic point of view between book lying stationary on horizontal table and rain drop falling down with constant speed? I can find two similarities Force acting on them is ...
0
votes
4answers
84 views

Dot product of vector and its derivative with respect to time? How does $L \cdot\frac{dL}{dt} = \frac{1}{2}\frac{d(L^2)}{dt}$? [on hold]

How does: $$L \cdot\frac{dL}{dt} = \frac{1}{2}\frac{d(L^2)}{dt}$$ where L is a vector (I dunno how to make it bold in the equation). How do they reach to this right hand side equation? And what is ...
1
vote
2answers
59 views

How is the integrand concluded to be identically zero?

In expanding the classical Klein-Gordon field in Fourier space to write it in terms of $\phi(\mathbf{p})$ instead of $\phi(\mathbf{x})$, I reached the following result. $$\int ...
-1
votes
1answer
48 views

Finding dv/dx when given x and v as functions of t [on hold]

This isn't a homework question, I tried to word this as a physical problem and it got re tagged as homework by someone Say I am given the equation of position in one dimensional kinematics. Say its ...
1
vote
0answers
29 views

How to find momentum of different pieces of the same object after it explodes?

If a stationery object explodes into a specific number of pieces due to internal force, how can I find the momentum of these pieces?
1
vote
2answers
29 views

Finding coefficient of friction between block and plane [on hold]

An inclined plane makes angle $\theta$ with horizontal. Upper half plane is perfectly smooth where as lower half is rough. The block of mass m starts sliding from top. If the block again comes to rest ...
1
vote
1answer
27 views

Two spherical cavities hollowed out from the interior of a conducting sphere. At the center of each cavity a point charge is placed

From Griffiths: Two spherical cavities, of radii a and b, are hollowed out from the interior of a (neutral) conducting sphere of radius R. At the center of each cavity a point charge is placed – ...
1
vote
2answers
78 views

Determining the Wave Function From Initial Conditions

This is Problem 2.6 (b) in Griffiths, Intro to QM: A particle in an infinite square well has its initial wave function an even mixture of the first two stationary states: $\Psi(x,0) = ...
1
vote
0answers
36 views

Heat transfer to a cube from one of the faces [on hold]

Heat Flux= 10 MW Inlet water temperature = 28 degree centigrade for cooling purpose through a tube passing through the centre of retangular block of length 50 mm,height 30 mm and width 30 mm inner ...
3
votes
3answers
51 views

What is the relative velocity of this plane relative to the helicopter? [on hold]

There is a plane moving 100 m/s due east relative to the ground without vertical motion. There is a helicopter facing north moving straight up at 20 m/s. From the perspective of the helicopter, is the ...
1
vote
1answer
49 views

An electromagnetic induction problem [on hold]

The question goes like this : A thin non conducting horizontal disc of mass $m$ having total charge $q$ distributed uniformly over its surface, can rotate freely about its own axis. Initially ...
1
vote
0answers
21 views

What is the angle of projection when at maximum height the speed of a projectile is half the speed at half the maximum height? [on hold]

I have been struggling with this problem: The speed of a projectile when it reaches its maximum height is one half of its speed when it is at half its maximum height. What is the initial ...
-1
votes
0answers
27 views

Yaw, pitch, roll: iOS -> android? [on hold]

The title contains names of mobile platforms but they are just examples and the question is independent from them. The problem. Yaw, pitch, roll and azimuth - all represent rotation angles around ...
1
vote
1answer
28 views

Modeling a stool with three legs pushed on one leg

If a stool with three legs is pushed (horizontally) on one leg in the direction of the axis passing through the other two legs, it starts both moving and rotating. Is it correct to assume 1/3 of ...
1
vote
3answers
43 views

Finding the density of gold crown using archimedes principle [on hold]

Question: As shown in diagram below the crown has a mass of 14.7kg when measured above water and 13.4kg when measured in water. Is the crown made of gold? I have this following solution provided: ...
0
votes
1answer
18 views

Finding height of floating iceblock above seawater [on hold]

This may be a very simple question but somehow I can't seems to solve it. For the sake of completness, I will use the same original question I am working on. Question: The density of ice is $917 ...
0
votes
1answer
34 views

Ray Tracing and Combination of Lenses [closed]

I was looking at this problem. Does the problem assume that the focal point of the divergent lens is right next to it? The answer is c, saying that the focus point will be further away: but that ...
0
votes
2answers
39 views

Given a slanted pipe

Question: I have a pipeline that is tilted. I know the length of the pipeline, and the pressure (90psi) that is felt at the very bottom. I'm trying to find out how much liquid has leaked out if the ...
0
votes
0answers
30 views

How to calculate the electric field for a charged tube? [closed]

Let's imagine there is a non-conducting charged tube with uniform charge distribution. (Simply a cylinder with no top, bottom and inside. I mean a roll of 2 dimensional paper but there is no inside. I ...
0
votes
0answers
38 views

Making a substitution to transform into a diffusion equation [closed]

I've derived the following equation for an accretion disk for fluid orbiting a central object at radius $R$: $$\frac{\partial\Sigma}{\partial t}=\frac{1}{R}\frac{\partial}{\partial ...
1
vote
1answer
37 views

Calculating the magnetic field due to a rotating ring using Biot–Savart law

I wish to calculate the magnetic field due to a charged ring rotating about an axis perpendicular to the plane of the ring and passing through a point on its circumference $(P)$. I arrive at something ...
0
votes
1answer
16 views

how to find max shear stress at a given point? [closed]

The state of plane-stress at a point is given by σx = -200 MPa, σy = 100 MPa, σxy = 100 MPa The Maximum shear stress (in MPa) is: A) 111.8 B) 150.1 C) 180.3 D) 223.6 Explain Procedure also with ...
1
vote
1answer
43 views

Will A Vertical Projectile Travel the Same Distance as A Horizontal Projectile

If a projectile is fired vertically from an initial height, $h$, above ground level, and an identical projectile is fired with equal initial velocity from the same initial height in the horizontal ...
1
vote
2answers
69 views

Force applied to an inclined plane

Below is a picture of the problem. Any guidance would be helpful. This problem isn't actually from any assignment, per se. I'm hoping that, by understanding this, it'll help me to understand a ...
0
votes
1answer
66 views

Finding equilibrium of mechanical system

A system is described as follows: Consider a system consisting of two rotating bars of length $l$ and with uniform mass density and each with total mass $m$. The bars are attached to a common ...
0
votes
1answer
42 views

Computing average force exerted by ground when jumping

Problem: A man of mass $m$ jumps vertically into the air from a sitting position in which his center of mass (CoM) is at a height $h_1$. When his feet are just about to leave the ground his CoM is at ...
0
votes
0answers
29 views

Find the relation between the displacements [closed]

Let there be a pulley moving downwards. It has mass $m_1$ to the left and $m_2$ to the right(latter has greater mass). Let in time interval $t$ , the pulley moves from $C$ to $C^`$ ; $m_1$ moves from ...