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.

learn more… | top users | synonyms (3)

1
vote
0answers
29 views

Does the induced Electric field develop instantly or lags by $\frac rc$?

Consider a loop of radius $r_0=3 \times 10^8$ cm. A thin bar magnet is passed through its center. This implies that the magnetic flux through the loop will change. Now according to Faraday's law a non ...
-1
votes
0answers
10 views

Proving the angle of inclination of the thread to the horizontal [on hold]

The problem: Two beads of weights $w$ and $w'$ can slide with negligible friction on a circular wire in a vertical plane. The beads are connected by a fine taut thread which subtends and angle ...
0
votes
0answers
19 views

Solving for masses in a Atwood machine system

So I'm confused on this problem for my college physics class: A simple Atwood's machine uses two masses, $m_1$ and $m_2$. Starting from rest, the speed of the two masses is 10.0 m/s at the end of 6.0 ...
0
votes
1answer
35 views

Why isn't this a valid derivation of the formula for capacitors in series?

I had to derive the formula for capacitors (I decided to use m capacitors in my derivation) in series, and this is what I did. The formula for a capacitor is $$Q=CV,$$ which is the same as saying ...
0
votes
1answer
19 views

Finding the voltage of the circuit?

Capacitor 3 in Figure (a) is a variable capacitor (its capacitance C3 can be varied). Figure (b) gives the electric potential V1 across capacitor 1 versus C3. The horizontal scale is set by C3s = 20 ...
-1
votes
0answers
23 views

Finding period of wave using its velocity [on hold]

I am trying to find the period of the oscillation wave. The string is 0.59 m long with tension 10.00 N. The total mass of the string is 13.42 g. Wave: I found the u (m/L) to be 0.0227 kg/m, from ...
-1
votes
1answer
22 views

How to calculate objects velocity after ataching to surface with a pole [on hold]

How do I calculate object's velocity after it has attached it self to a surface with a stick (by stick I mean it is not a spring or rope, it does not bend)? I need it for the video game I am making. ...
1
vote
2answers
41 views

Potentials with no sources

I have been reading Electrostatics from Panofsky's book. One of the exercises in his first chapter is Functions of the type $\phi = x$, or indeed $\phi = x^2 + 2 y^2 - 3z^2$ , satisfy Laplace's ...
-1
votes
1answer
37 views

Tension of string attached to ball on inclined plane [on hold]

A sphere of weight 50N and radius 4cm is held by a string of length 8 cm against a smooth wall inclined at an angle of $70^{\circ}$. Find the tension in the string and the force between the ball and ...
1
vote
0answers
22 views

Beat Frequency for Police Radar with Special Relativity

"A radar speed trap operates on a frequency $v_o = 109 Hz$. What is the beat frequency between the transmitted signal and one received after reflection from a car moving at v = 30 m/s toward the ...
0
votes
0answers
35 views

Energy-Momentum Tensor of Spinors on Curved Spacetime

Well, I am trying to derive the stress-energy tensor for Dirac fields on a curved spacetime using tetrads, despite knowing how to calculate it using another formalism. The thing is, I already ...
-1
votes
0answers
13 views

A problem related to the Temperature Coefficient of Resistance [on hold]

I'm having some problem understanding this temperature Coefficient α. I have some questions. I think it doesn't always constant. It just stays constant for a small variation in temperature. Am I ...
-1
votes
1answer
20 views

Speed of efflux of an ideal fluid [on hold]

My situation: I have to calculate the speed of efflux where the water runs into the bottle. I tried to apply Bernoulli's principle but this doesn't work out as I end up with $0 = ...
-1
votes
2answers
37 views

What is the shape of a gravitation field for a square or cubed mass (say, size of a planet)?

most gravitation models assume a round object as most large masses in space (planets) are more or less round. It is simple to envision that it gravitation pull is also [nicely spherical and diminishes ...
-1
votes
1answer
29 views

Help understanding “Pushing blocks against headwind” [on hold]

I am new to StackExchange Physics so I apologize if I do any mistakes. I have been given a problem in dynamics and I have been working on it for a while but I am just getting nonsense. The problem ...
-2
votes
0answers
28 views

A tank of the shape of a right circular cylinder $5$ feet across the top and $9$ feet deep is full of water. [on hold]

A tank of the shape of a right circular cylinder $5$ feet across the top and $9$ feet deep is full of water. How much work is done by pumping the water out of the tank, over the top edge? I need your ...
-1
votes
0answers
44 views

Mechanics; find the equation's path [on hold]

I'm beginning in Mechanics and trying to solve this exercise : We have an orthonormal plan, the coordinates of a moving point M are defined according to time by : $$x(t)=a \sin(\omega t)$$ $$y(t)=b ...
0
votes
1answer
25 views

Steel rod compression under gravity [on hold]

A steel rod with length lying down of 100m (youngs modulus = 200GPa, density 7.85g/cm^3) is stood upwright. How much does it compress by after it is stood upwright. So far I'm just using the formula ...
3
votes
1answer
90 views

What is the force required to move a raindrop?

I'm doing some research on how much force is required to move a typical raindrop (assuming that it is falling straight down) off to the side of X distance. This is for a school project on creating our ...
-1
votes
2answers
53 views

How does gravitational potential energy increase, if field decreases as $h$ increases?

(constants're ommitted) 1-) M=50, m=5, h=5 then Potential Energy = (50*5)/5 = 50 After increasing height 2-) M=50, m=5, h=10 then Potential Energy = (50*5)/10 = 25 Field strength decreases amount ...
-1
votes
0answers
18 views

Compton scattering - going from $θγ^*$ to $θ_{elec}$ [on hold]

I do have the following problem about compton scattering: Find a formula for $$θ_{elec} = f(E_{beam}, \lambda, \theta \gamma^*=90).$$ In other words, how can I go from the rest frame of the photon ...
-2
votes
0answers
20 views

physics - kinematics [on hold]

Two particles one with constant velocity 50m/s and other with uniform acceleration 10m/s2,start moving simultaneously from the same plane in same direction.they will be at a distance of 125m from each ...
0
votes
1answer
51 views

What is the covariant basis around a Schwarzschild black hole?

First of all, I'm not interested in time for this question. So lets consider a 3-manifold whose metric is the spatial part of the Schwarzschild metric, so it has the event horizon and the singularity ...
-1
votes
0answers
19 views

Calculate weight of one object suspended on a wire given angle of depression of wire and weight of another object [on hold]

Suppose I attach two objects to the left and right end of a sturdy wire whose folcrum is in the middle. The wire can't fall off. Using a horizontal line as my guide, I pull out a protractor and ...
-1
votes
0answers
16 views

Commutative Observables Expressed as Functions of a Third Observable [on hold]

For my Quantum assignment, I have to prove that, if two observable operators A and B commute $\exists C $ s.t. A = f(C) and B=g(C) for some real-valued functions f and g. I'd appreciate any amount of ...
2
votes
0answers
33 views

Rod rotated by elastic string [on hold]

A uniform rod $AB$ of length 2m and mass 1kg, has a mass of 1kg attached at $B$. It can rotate freely about a horizontal axis through $A$. The end $B$ is attached by means of a light elastic string ...
-2
votes
0answers
17 views

Finding the overall speed of the car? [on hold]

A car drives $10~\text{km}$ to the east in $15~\text{min}$. Then it turns around and drives $4~\text{km}$ to the west in $15~\text{min}$. What is the overall speed?
0
votes
1answer
58 views

What is the total matter equivalent of the Sun's output per year?

Say we can collect all the energy from the sun's output and all the particles from the solar wind. If we had an energy to mass converter and turned everything into say, carbon, how many kilograms of ...
-2
votes
0answers
17 views

I need help with this question requiring the distance of null electric field [on hold]

The question goes: Two charges q1=-10^-5 C and q2=-9x10^-5 C are placed respectively at two points A and B, 40 cm apart. The electric field is null at point C. Find AC I have tried getting the force ...
-4
votes
0answers
17 views

I need help with this question on electric fields [on hold]

Two charges q1=-10^-5 C and q2=-9x10^-5 C are placed at two points A and B, 40 cm apart. The electric field is null at point C. Find AC
3
votes
0answers
73 views

Calculation of water bulk modulus using equation of state

I simply want to calculate the bulk modulus of water at 50C and increasing pressures. I think I am correctly calculating the new specific volume from the original conditions at (25C and 1atm) to 50C ...
0
votes
0answers
42 views

Plasticine experiment [on hold]

I am doing an experiment in my high school, with plasticine (I did not choose it, it was stupidly given to us). So my idea is to see how the diameter of a plasticine ball (flat bit) varies with the ...
2
votes
2answers
43 views

Basic Relativistic Question - length measurement

A while ago we did an easy, introductory exercise on length measurement. Back then it seemed pretty straightforward but now when I look at it I have trouble understanding the assumption which led to ...
1
vote
0answers
27 views

Exercise about Bethe Ansatz for $N=3$ particles on a ring of length $L$

Suppose there are $3$ bosons living on a 1-dimensional ring of length $L$. The Hamiltonian is given by $$H=-\sum_{i=1}^3\frac{\partial^2}{\partial x_i^2}+\sum_{1\leq j<k\leq ...
0
votes
0answers
31 views

How does the gravitational force exerted on earth? [on hold]

The sun’s mass is about 2.7 x 107 times greater than the moon’s mass. The sun is about 400 times farther from Earth than the moon. How does the gravitational force exerted on Earth by the sun compare ...
-4
votes
0answers
25 views

How high above Earth's surface would you have to be? [on hold]

Using 6400 km as the radius of Earth, how high above Earth’s surface you would have to be in order to weigh 1/16th of your current weight?
-2
votes
0answers
34 views

Could you please explain whether each of the following is possible for the pilot to measure? [on hold]

An airplane has a gun that fires bullets straight ahead at the speed of 600 miles per hour when tested on the ground while the plane is stationary. The plane takes off and flies east at 600 miles ...
-2
votes
1answer
32 views

Could you please help me find another example of motion under null net force? [on hold]

There are many familiar situations in which the net force on a body is zero and yet the body moves with a constant velocity. Here is one example: A car traveling at constant speed on a ...
0
votes
0answers
28 views

Propagator massless particle in 1D [on hold]

For a condensed matter application I want to solve the following equation $$ -(\alpha^2 - i \partial_z)G(z,z') = \delta(z-z'). $$ Basically, $G(z,z')$ is the Green's function for a particle with a ...
5
votes
2answers
115 views

Lorentz transformation paradox

I got to solve a simple exercise about special relativity when I kinda came to the conclusion it doesn't stroke with my intuition. The homework-problem The problem was about two people Sam and ...
-1
votes
0answers
17 views

Lorentz force solving and integration [on hold]

I have a question on how to get gyro frequency from lorentz equation. The question is attached below. I have also attached what I have done so far, but looks wrong. How is this question done; a) ...
1
vote
2answers
84 views

Oscillations Near Equilibrium (With Linear Differential Equations)

Case I: The force acting on an object of mass m is $F(x) = F_o(1-e^{\alpha x})$ Case II: The force acting on an object of mass m is $F(x) = F_o(1-e^{-\alpha x})$ where $F_o$ and $\alpha$ are ...
3
votes
3answers
38 views

The storage of kinetic energy in a flywhell?

I am reading a book on physics demonstrations and problems, and one of the problems deals with a flywheel which rotates at maximum angular speed. The density of the flywheel is uniform and the ...
2
votes
1answer
15 views

How do I find the angle with respect to the ground that will cause a projectile launched from the origin to land at the origin? [on hold]

Given an arbitrary non-zero constant horizontal acceleration (like a breeze perhaps), how would one find the angle with respect to the ground (x-axis) that will cause a projectile launched from the ...
3
votes
1answer
62 views

Laser, wire, and a circle of light

So, when I point a laser at a piece of wire (pointed at a specific angle), a circle of light appears on a wall behind it (see image below). I am trying to see why this happens and if there are any ...
1
vote
1answer
34 views

Ladder operators evolution for fermions

For the free Dirac field we have $$ \psi(x) = \sum_s\int d\Omega_{m}\frac{1}{\sqrt{2}k_0}\left(b(\mathbf{k},s)u(\mathbf{k},s)e^{-ik\cdot x}+d^\dagger(\mathbf{k},s)v(\mathbf{k},s)e^{+ik\cdot ...
1
vote
3answers
74 views

A problem related to Work done by falling bodies : Expert's attention much needed! [on hold]

I'm having a lot of trouble with this question, that I've found in my textbook. I've solved it in my own way and it's very simple! But the solution in the book is totally different. It doesn't make ...
4
votes
2answers
103 views

Rectangular window $\psi$ wave-function and the calculus of $\langle p^2\rangle$ for it

I'm currently considering a rectangular window $\psi$ function: $$ \psi(x) = \begin{cases}\left(2a\right)^{-1/2}&\text{for } |x|<a \\ 0&\text{otherwise.} \end{cases} $$ I am interested in ...
2
votes
1answer
48 views

Transformation of the scalar field under Lorentz Boost [on hold]

Assume a Lorentz transformation $\Lambda$ is to be implemented as the unitary operator $U(\Lambda)$ in the Hilbert space of quantum states of the Fock representation upon which the scalar Klein-Gordon ...
0
votes
0answers
29 views

Deceleration of a space shuttle [on hold]

A space shuttle is decelerated by parachutes, which cause a deceleration of $a(v)=-0.04 v^2$. After what time is a space shuttle decelerated to $1m/s$ if it had a velocity of $50m/s$ when the ...