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
5 views

Rolling on a frictionless pond

I have a doubt about one of the questions in my textbook. Q- You are standing with your bag in your hands in the middle of a friction-less pond. How can you come out of the ice? There is of ...
0
votes
0answers
26 views

Derivative of unit vectors in polar coordinates

My book shows an example on how to differentiate the 2 polar plane unit vectors but they deduce it from a graph that dosen't make any sense to me what so ever. Is there an algebraic way? Or if not, do ...
1
vote
2answers
29 views

Expectation value with plane waves

Hey guys Im a little confused with the concept of plane waves and how to perform an expectation value. Let me show you by an example. Suppose you have a wave function of the form ...
0
votes
1answer
35 views

Question on Einstein's derivation of the equation of the geodesic line?

While reading one of the original paper on general relativity written by Albert Einstein, titled the foundations of general relativity, I came across the following passage in pages 167-168, or pages ...
-1
votes
0answers
10 views

The conservation of energy with pulleys and belt on a support turning

A big pulley (radius 3R) turns clockwise at -2w. A small pulley (radius R) turns clockwise at -6w. These pulleys are put on a support (green), the support turns clockwise at -w. A motor fixed on the ...
0
votes
0answers
27 views

How do I combine three spins?

So I've just learnt about coupled and uncoupled bases and the like. I'm trying to solve a problem that deals with combining three spins (I haven't done this before). The spins are $1, 1/2$ and $1/2$. ...
0
votes
1answer
14 views

Flow rate through hole at bottom of tank, estimate time for depth to reach 1 foot

I am a structural engineering student and have limited experience in fluid dynamics. I'm not quite sure if I'm going about the problem in the correct way. The question is: An open cylinder of ...
-1
votes
0answers
39 views

Moments question

I tried and tried to do this question but cannot get the right answers. Can someone help me in determining the free body force diagram, and confirm whether or not it is best to take moments at C, ...
0
votes
1answer
31 views

Transformation of $q_k$ and $p_k$ from invariance of Hamiltonian

This is a step in Nakahara's Geometry, Topology and Physics, 2nd edition, 2003, on pages 7-8: Given that $q_k ' = q_k +\epsilon f_k(q)$, we have that $$\Lambda_{ij} = \frac{\partial q_i'}{\partial ...
-1
votes
1answer
26 views

Concept of the working of friction?

I have been trying to solve the exercises of HC Verma- Concepts of Physics. Can't understand the solution of one of the questions on friction. Question The friction coefficient between an a pair of ...
0
votes
1answer
27 views

Diffraction grating problem [on hold]

We have 8 slits, each separated from its neighbour by $ 0.05$mm. We use light of wavelength $576$nm. The problem is to calculate at what angle the first minimum occurs. The answer is given: ...
-1
votes
0answers
51 views

Coupled harmonic oscillators

I'm given the following exercise: Consider two identical particles (mass $M$ and spin $1/2$) in a harmonic oscillator potential, and the interaction between them is a harmonic oscillator depneding ...
0
votes
2answers
44 views

Optimal method for solving circuit

This problem seems quite simple, and I can easily find a way to solve it but the possibility of error in my method is extremely high. This is just a sub-task of a bigger task but this is the only part ...
0
votes
4answers
45 views

Current and voltage word problem [on hold]

If a conductor with a current of 200mA passing through it converts 40 J of electrical energy into heat in 30 seconds, what is the potential drop across the current ? The answer is 6KV, but I don't ...
-2
votes
0answers
27 views

Two site Hamiltonian matrix [duplicate]

So I am trying to write a matrix for a Hamiltonian and am having problems figuring it out. So the Hamiltonian is $$\epsilon_1\sigma^+_1 \sigma^-_1 + \epsilon_2\sigma^+_2 \sigma^-_2 + V_{12} ...
-5
votes
0answers
27 views

Distance of golf ball [duplicate]

Okay so I got number a magnitude by using $\mathtt{x} = \mathtt{v_0}\cdot\mathbf{t} +\dfrac{\mathtt{a}\cdot{\mathbf{t}}^2}{2}$ and for the horizontal as well which equals $16.19$. I also figured ...
-3
votes
0answers
21 views

Magnitude of initial velocity and horizontal distance [on hold]

please help me figure out how to solve the magnitude and number b. thanks
-1
votes
1answer
51 views

Two site Hamiltonian [on hold]

So my question is I have this Hamiltonian: $$ H = \sum_i \epsilon_i \sigma^+_i\sigma^-_i + \sum_{i\neq j} V_{ij} \sigma^+_i \sigma^-_j, $$ and I want to write it out for two site. Is this correct?: ...
0
votes
3answers
46 views

Vector question, differentials, Electromagnetism

I was reading this demonstration of electric potential in my book: Let $q$ be a point charge at point $P$ The Electric field created at point $M$ by $q$ is : $$\vec{E}(M) = ...
2
votes
1answer
47 views

Does equality of operators on vacuum imply equality of operators on the whole space?

Consider a field operator $\Phi(x)$ which generates states from the vacuum such as $$ \tag 1 | x \rangle = \Phi(x) | 0 \rangle.$$ Consider also how a translation is implemented on such a state: $$ ...
0
votes
2answers
286 views

Olympiad physics 1996 problem [on hold]

I don't understand the official solution of the first problem of the 1996 International Physics Olympiad. They give this circuit: Each black box is a resistor of resistance $1\Omega$. They then ...
-1
votes
1answer
23 views

Statics question: Calculate thrust force [on hold]

First and foremost can someone explain what is being asked here please?
-1
votes
0answers
33 views

Electric field of two charges in point (0,0) [on hold]

I have a question about calculating electric field. In the given image you have two line charges which are not infinite. “a” is a radius, and angle “alfa” is given. How to calcululate electric field ...
0
votes
1answer
37 views

Duality and 1 forms

If a Killing vector is equal to: $$X= -\frac{1}{\sqrt{2}}\partial _t + \frac{\alpha}{\sqrt{2}}\partial_1.$$ But as far as I know is that the dual of a vector is a 1-form, so can I represent that ...
2
votes
3answers
67 views

Determining a temperature increase from heat energy [on hold]

A 15.0g bullet traveling horizontally at 865 $\frac{m}{s}$ passes through at a tank containing $13.5$kg of water and emerges with a speed of $534\frac{m}{s}$. What is the maximum temperature ...
3
votes
2answers
92 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
1answer
36 views

Multiplication properties about trace of two operators [on hold]

Consider two operators $A$ and $B$, their functions $e^A$ and $e^B$ and a basis that mutual diagonalizes $A$ and $B$. Can I say that $$Tr\left[e^Ae^B\right]=Tr\left[e^A\right]Tr\left[e^B\right]~?$$ ...
0
votes
0answers
26 views

Solving for masses in a Atwood machine system [on hold]

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 ...
1
vote
1answer
45 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
55 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
24 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
25 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
43 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
42 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
40 views

Energy-Momentum Tensor of Spinors on Curved Spacetime [on hold]

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
15 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 = ...
0
votes
2answers
38 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
32 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
46 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
91 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 ...
0
votes
2answers
67 views

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

(In the following constants are ommitted) Let $ M = 50, m = 5, h = 5$. Then $$ \text{Potential Energy} = \frac{50\cdot5}{5} = 50.$$ While after increasing the height $h$: $ M = 50 , m =5, h =10 ...
-1
votes
0answers
19 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
54 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
20 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 ...