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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1answer
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Finding the torque on a dipole affected by electric field

A $H_2$ molecule with charges $\pm p$ separated by $d=10^{-10}$m and masses $1.66\times 10^{-27}$kg is put into an electric field with uniform strength $E$, making an angle $\theta$ with this field. ...
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1answer
22 views

Pulling a bar through a magnetic field

This is a question on magnetic flux and induced voltage. I believe that this problem's answer key is incorrect, and I want to determine whether my opinion is sound. I also want to explore one ...
1
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1answer
10 views

2D square lattice, nearest neighbor and next-nearest connected by springs

For my field theory class I am trying to build the Lagrangian for the following system. Consider a 2D square lattice where the nearest and next-nearest neighbor interactions are modeled by springs ...
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0answers
22 views

Finding force acting on an object using work energy theorem

An object of mass 5kg passes through the origin at $t=0$. $x$-component of velocity is 4 and $y$-component is -3. At a later time $t=3$ the object is located at $x=9$ and $y=5$. What is the force ...
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1answer
40 views

Using differentials to optimize a function

I've read in a paper by Tevian Dray an alternative way to solve optimization problems manipulating "differentials". Here is an example of how it works (next I quote the paper). Consider the ...
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0answers
30 views

Calculation of angular acceleration [on hold]

Hi I am doing a physics question and it's like this: Two identical blocks, each of mass M, are connected by a massless string over a pulley of radius R and rotational inertia I . When the system is ...
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0answers
17 views

Calculating the entropy of a monatomic ideal gas

I am looking at the start of the consider how to calculate the entropy of a monatomic ideal gas. We need to determine the number of microstates in $E \leq \mathcal{H}(\Gamma) \leq E+\Delta$. The ...
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1answer
32 views

How do i correctly go from a two variable function to a function of difference?

I would like to know how I can go from a two argument function $g(x_1,x_2)$ formally correct to a function of the difference of the parameters $g(x_1-x_2)=g(x)$ this seems to involve integration over ...
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0answers
14 views

Equivalent force–couple system STATICS Meriam 6th exer. 2/71 [on hold]

I need a bit of help to clarify what I couldn't see here. 2/71 The system consisting of the bar OA, two identical pulleys, and a section of thin tape is subjected to the two 180-N tensile ...
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0answers
27 views

When does a balloon burst?

I'm working on a project and I need to know something. and that's : When does a balloon burst? I mean, does it have any relation to its internal pressure or its volume? for example can we say a volume ...
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0answers
13 views

Find the length of time for which the direction of motion is between 20 degree above and below the horizontal [on hold]

A particle is projected with speed $65\, m s^{−1}$ from a point on horizontal ground, in a direction making an angle of $\alpha$ above the horizontal. The particle reaches the ground again after $12\, ...
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3answers
50 views

What is meant by a “sodium line”?

What speed should a galaxy move with respect to us so that the sodium line at $589.0\ \mathrm{nm}$ is observed at $589.6\ \mathrm{nm}$? In the above question what's meant by a sodium line? The ...
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0answers
23 views

Acceleration of an incompressible fluid along a conical pipe [on hold]

I've been reading Theory of Flight by Richard von Mises and early on I came across this problem. The full text of the problem is as follows: "Show that along a conical pipe the acceleration of an ...
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2answers
28 views

Pendulum point in polar coordinates for Lagrangian

So I'm really stumped with this. I have a particle in a cone, like pictured. The particle orbits the z axis on the dotted line for $r$. So knowing that $\alpha$ and $r$ remain constant in this ...
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2answers
20 views

Radiometric dating calculation [on hold]

If a sample of zircon initially contains no Lead, find an expression for the ratio $$\frac{N_U}{N_{Pb}}$$ as a function of time? How do I do simplifications from this? Do I just go: ...
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0answers
14 views

Force and tension on a set of ropes [on hold]

I'm having trouble figuring out what to do after getting the force acting on lines AB and BC (I'm getting about 117N), how do I figure out the forces on BC, BD, and CE? Since the system is ...
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1answer
20 views

How to calculate error of this powers? [on hold]

How to find the error of this? 3*{10^ ([m sun - m c]/2.5)} If m sun or the apparent magnitude of the sun=-26.7and doesn't identify its error. And m c =23.79+- 0.26 My work is: For m sun-m c= -50.49 ...
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1answer
27 views

Conserved current in a complex relativistic scalar field

For my field theory class I have the following Lagrangian density $$\mathscr{L}=\frac{1}{2}\eta^{\mu\nu}\partial_\mu\phi^*\partial_\nu\phi-\frac{1}{2}m^2\phi^*\phi$$ Where $\eta^{\mu\nu}$ is the ...
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1answer
30 views

How does the equation $1/I = r/E +R/E$ relate to $ y=mx+c$? [duplicate]

I have a graph of $1/$current against resistance, which is a straight line of positive gradient. I know that the gradient represents $1/V$ but I can't work out how the equation $1/I= r/E + R/E$ ...
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0answers
31 views

Potential difference between Earth's surface and 2 meters above

Assuming Earth is a charged sphere of radius $R = 6400.10^3 m$ with uniform surface charge density $\sigma = -10^{-9} C.m^{-2}$ and with $\epsilon_0 = 8.85.10^{-12}F.m^{-1}$ I find that ...
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3answers
43 views

Tension Problem: Finding an angle when only given the tension in two ropes [on hold]

A crate is hanging from a rope which is attached to a metal ring through which a second rope runs, as shown to the right. What is the angle $\theta$ if the tension in rope 1 is $1.19$ times the ...
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2answers
32 views

Calculating the time constant for charging a capacitor in a circuit [on hold]

Problem: Calculate the time constant for charging the capacitor in the shown circuit. What is the maximal charge on the capacitor? Attempt at a solution: Let current $I_1$ flow from the emf ...
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0answers
19 views

What would be the formula for the time to impact of an object travelling at a constant velocity? [on hold]

What would be the formula for the impact time of an object? Assuming that the object is falling at a constant velocity, for example, the object is falling at 5 m/s, and is 50 meters away from the ...
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1answer
30 views

Potential energies of charges and spring

I wonder if someone could sanity check this very simple calculation. Consider a pair of charges $+q$ at rest separated by a spring of length $d$ and stiffness $k$. The spring provides the force that ...
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0answers
20 views

Moment of inertia question 11 [on hold]

A circular disc of radius $R$ and mass $M$ has non uniform surface mass density $ar^2$ where $r$ is the distance from the center of the disc and $a$ is a constant.what is the moment of inertia about ...
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1answer
28 views

Relativistic addition of velocities in the y-direction? [on hold]

I've been having some difficulty with the problem described below, please have a look: Two particles with identical masses (m) undergo a collision. Before the collision they move with velocities ...
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1answer
62 views

How to calculate the energy required to rotate a planet?

How to calculate the energy required to rotate a planet from non-rotating state? Say the planet is Venus with equally distributed mass of $4.8676 \times 10^{24}$ kg, and desired rate of 1 rotation per ...
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0answers
27 views

Identity for the product of propagators

Working in 1 spacial dimension, it has been written that $$\begin{align} \int K(x_f,x,t_2)K(x,x_0,t_1)dx &= \int \langle x_f|e^{-\frac{i}{\hbar}\hat{H}t_2}|x\rangle \langle ...
0
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0answers
32 views

How to write the energy for a system of beams? [on hold]

Goodmorning to everybody. In my problem I would like to write the energy of a system of 3 beams (see the link below), clamped together in A, positioned at 120° one to each other. ...
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0answers
14 views

What is the minimum required length of mirror to view full object if the mirror is convex?

i want to find the Radius of curvature of a convex mirror. i have all the factors to calculate except for image height of an object and image distane. so i can find the image height of an object from ...
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0answers
36 views

Feynman Propagator in Position Space through Schwinger Parameter

So I am aware of a thread at Propagator of a scalar in position space but it does not answer my question, which is more about poles in position space. Starting from $$D_F(x_1-x_2) = \int \frac{d^4 ...
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0answers
20 views

Inquisitive please help me!! Finding charge on plastic spheres [on hold]

A piece of wool is used to charge two plastic spheres. When the spheres are held 300mm apart, they repel each other with 9.00N of force. If the wool ends up with a surplus positive charge of 29.5μC , ...
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0answers
18 views

Dipole moment of a specific charge distribution

A negative charge cloud distribute as a ellipsoid and a positive point charge situated at the centre of the ellipsoid.What should be the dipole moment of charge distribution.I mean, if the negative ...
0
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1answer
32 views

Solving for the density operator in the quantum Brownian motion master equation

I want to solve for the density operator in the quantum Brownian motion master equation, \begin{align} \begin{aligned} ...
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2answers
57 views

Orbital Velocity Question

I have a satellite in a stable trajectory around Earth, of a Mass $m$. I know that its velocity is: $$ v = \sqrt{mG/r}\, $$ But now it begins accelerating directly against the gravity vector (i.e. ...
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2answers
38 views

Convert cubic feet per sec to feet per sec

Is there a way to convert cubic feet per sec to feet per sec. Or in general volumetric flow to velocity? I want to know the time taken by water to travel from point A to point B. I have the distance ...
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2answers
79 views

Triangular barrier in infinite potential well

Suppose I am looking to solve the wavefunction for the following 1D potential: $$U(x) = \begin{cases}V_0\frac{a-|x|}{a}&\quad\text{for}\quad|x|<a ...
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0answers
38 views

How is tunneling probability? [on hold]

Let's say we have an alpha particle tunneling through a barrier of width 2 fm and height 30 MeV, and the alpha particle has an energy 1 MeV below that of the barrier. The tunneling probability is ...
-3
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0answers
13 views

Computational hydraulics [on hold]

Find the emptying time for reservoir that the water level drops from 35m to 25m using following data: - V=15000 h volume-elevation relationship for reservoir - D=2m diameter for outlet works - h' ...
-2
votes
1answer
30 views

Probability with expectational value [on hold]

How can I calculate: $$P(T)=T^2 b^2 |<n| \delta (x) |n>|^2~?$$ Where $P$ is the probability.
1
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2answers
36 views

Show that a function takes the following form using the definition for the function of an operator

If $f(z)$ is a function with a Taylor series expansion $$f(z)=\sum _{ n=0 }^{ \infty }{c_n z^n },$$ then we define $$f(M)=\sum _{ n=0 }^{ \infty }{c_n M^n }.$$ First consider ...
0
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0answers
35 views

Why is entropy in a heat flow process always positive? [on hold]

Entropy in a quasistatic heat flow process is given by $$\Delta S=C_1\ln(\frac{T_f}{T_{10}})+C_2\ln(\frac{T_f}{T_{20}})$$ Where $C_1, C_2$ are heat capacities at constant volume, $T_{10}<T_{20}$, ...
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0answers
20 views

Thermal conductivity of oak wood [on hold]

How do I calculate the thermal conductivity of a natural material (oak wood) having only the data of two considered temperatures for the heat transfer and the time that it takes for the sample to ...
0
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1answer
27 views

Equations for a collision between two particles

Say I have two particles on a 2D plane, they have a x and y coordinate, a x and y velocity, a mass, a coefficient of restitution and a coefficient of friction. What formulae would I need to determine ...
-1
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0answers
21 views

Launching a Spring from a meter stick [on hold]

In class we are engaging in 'war games'. We receive a random spring and launch it from a meterstick at a target flat on a nearby table. we will have the variables for: ...
0
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1answer
22 views

Influence of a defect on the flow field

I have a long microchannel where flows some water. The reynolds number is much smaller than one. Within the structure of this microchannel there is a big defect. It looks like a bump of size ...
1
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0answers
20 views

Decomposition into symmetric and antisymmetric form [on hold]

(a) Given a second-rank tensor Tμν, often viewed as an $N \times N$ matrix (for a space of dimension $N$), show by explicit construction that one can always decompose $T_{\mu\nu}$ into a symmetric ...
0
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0answers
33 views

Computing And Finding The Trajectory From The Lagrangian [on hold]

The Euler–Lagrange equations come from extremization of the action. So we expect the "true", dynamical trajectory to minimize (in this case) the value of $S=\int L \,dt$ For free particle motion, the ...
-3
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0answers
38 views

Generate the equations of motion for the one-dimensional Lagrangian [on hold]

Generate the equations of motion for the one-dimensional Lagrangian: $$L=\frac {1}{2}m\dot{x}^2-(Ax+B)$$ From the equations of motion (and the implicit definition of the potential), provide a physical ...