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.

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0
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1answer
202 views

a metal bar on a pair of conducting rails that carries a current

This is a homework question, and I solved it already, but something bugs me. So the problem is stated as following: A metal bar of mass M sits on a pair of long horizontal conducting rails separated ...
-1
votes
1answer
173 views

New to physics and need some help with understanding acceleration [closed]

The free fall acceleration of an object under earth's gravity is directed toward? When the same amount of force is applied to two different masses, the smaller mass will be accelerated ____ than the ...
2
votes
3answers
720 views

Maxwell Stress Tensor in the absence of a magnetic field

I'm having some trouble calculating the stress tensor in the case of a static electric field without a magnetic field. Following the derivation on Wikipedia, Start with Lorentz force: $$\mathbf{F} = ...
0
votes
1answer
96 views

Potential energy and average force? [closed]

A body of mass $15\,kg$ originally at rest $5\,m$ above the ground falls and penetrates $15\,cm$ into soft earth. Determine the loss of potential energy Determine the average resistance of the ...
2
votes
1answer
709 views

Static Friction in Free Body Diagram (FBD) of Car parked on Incline

I'm working on a sample problem and it asks on how steep of an incline can a car park? From what I learned the friction is in the opposite direction if there was motion in said friction-less ...
0
votes
4answers
279 views

Why is there a potential difference?

The question then asks for the potential difference between $X$ and $Y$, which is claimed to be $3.6\text{ volts}%$. Why would there be a potential difference in this case? If I connect a lightbulb ...
1
vote
2answers
799 views

Finding maximum speed in a work-energy problem

I have the following problem: The Royal Gorge bridge over the Arkansas River is $310\text{ m}$ above the river. A $57\text{ kg}$ bungee jumper has an elastic cord with an unstressed length of ...
1
vote
1answer
298 views

Two Qubit problem

A two-qubit system was originally in the state $ \frac{3}{4}|00\rangle-\frac{\sqrt{5}}{4}|01\rangle+\frac{1}{4}|10\rangle-\frac{1}{4}|11\rangle $ , and then we measured the first qubit to ...
1
vote
1answer
102 views

Distance traveled in a simple two body problem [duplicate]

I'm trying to program an $N$-body simulation and I'd like to be able to test it with a known solution to a simple, two-body problem. I've looked at multiple sources, but I just don't know how to apply ...
2
votes
0answers
145 views

Internal moment in the hull of a pressure vessel

This question is related to the course structural analysis. As part of our exam grade every student has been given different multiple homework assignments which we have to solve. One of the problems ...
4
votes
3answers
82 views

Length of day of a gas giant

How can the rotational speed, or the length of a day be determined or estimated in a planet which is composed entirely of non homogeneous fluids? There must be internal forces (pressure gradients, ...
1
vote
3answers
193 views

How does upwards acceleration affect tension on whirling mass?

Consider the following setup and problem: When solving this problem, I had the intuition that the string tension $T_A$ would be equal to $T_B$, which does not agree with the solutions. What would ...
1
vote
3answers
459 views

kirchhoff's law.Simple question [closed]

So far I calculated total resistance and it is 4.66 ohms and there is 12 volt voltage across them, what is the best way or HOW to calculate current for each resistor ?
1
vote
0answers
81 views

Problem in average height

Let, diameter of cylinder hole of height 30m and diameter 2m filled with water. In a book, when author tried to find out the power for lifting all of the water then he used average height. why is ...
0
votes
2answers
757 views

Young's Double Slit experiment question

Q-A beam of light consisting of two wavelenghts 600 nm and 450 nm is used to obtain interference in Young's Double Slit experiment (YDSE). Find the least distance from the central maximum where the ...
3
votes
2answers
283 views

Find work done by force along a path - is parameterization the only way?

$F = x^3y^4 \hat i + x^4y^3 \hat j$ from $(0,0)$ to $(1,1)$. I am given different paths. For example, "first along x axis and then along the y axis" is one of the paths. Is this problem solvable ...
1
vote
0answers
163 views

I need help with the following Physics' questions [closed]

I need to know which formulas and the step-by-step answers for the following physics questions: 1. You throw a ball upward with an initial speed of 7.0 m/s, and it returns to your hand o.92 ...
1
vote
0answers
103 views

A 0.1kg ball of dough is thrown up with a velocity of 15m/s. What is the momentum halfway up? [closed]

I know that $p=mv$ and (0.1kg)(15m/s)=1.5 kg m/s and the momentum at the vertex is 0, but what is the momentum halfway up?
4
votes
2answers
675 views

Constant magnetic field applied to a quantum harmonic oscillator

I have a spinless particle of mass $m$ and charge $q$ which is an isotropic harmonic oscillator of frequency $\omega_0$, then I apply a constant magnetic field in the $z$ direction. We can show the ...
1
vote
1answer
277 views

Quantum Circuit, example of the Bernstein-Vazirani problem

This question is regarding the quantum circuit in the picture below. Suppose we have the set up below, where U performs the operation $U:\mid x \rangle \mid y \rangle \rightarrow \mid x \rangle\mid y ...
0
votes
1answer
296 views

Combining Conservation Laws ~ Homework Problem Guidance

Problem 8.79 - Combining Conservation Laws A 5.00-kg chunk of ice is sliding at 12.0 m/s on the floor of an ice-covered valley when it collides with and sticks to another 5.00-kg chunk of ice that is ...
0
votes
2answers
319 views

Lagrange-Euler equations for a bead moving on a ring

A bead with mass $m$ is free to glide on a ring that rotates about an axis with constant angular velocity. Form the Lagrange-Euler equations for the movement of the bead. Solution: Let us ...
2
votes
1answer
460 views

Covariant derivative

I would very much appreciate some help in The following: What is 2nd order covariant derivative $$\nabla_i\nabla_jf(r)$$ in terms of $r,\theta, g(r)$ and partial derivative, given that the metric ...
1
vote
0answers
315 views

Point charge moving towards a conducting plane

A point charge $q$ of mass $m$ is released from rest at a distance $d$ from an infinite grounded conducting plane. Show that the charge hits the plane after an amount of time given by: $ \Delta t= ...
1
vote
1answer
3k views

Needed Energy For Lifting 200 kg weight

I'd like to learn how much energy I need to lift a 200 kilograms weight on normal earth conditions? For example how much electric power do we need? I'm not a physicist and not a student and this ...
1
vote
0answers
47 views

Height of a piston in a heated cylinder containing H2O

I'm a first time user and I hope I won't be too enigmatic asking the following question: I have a cylinder (radius= $6$ $\text{cm}$) with a frictionless piston on top of it and inside $30$ $g$ of ...
1
vote
1answer
227 views

Thin lens formulae

Hi I have a question about applying the thin lens formula $$ \frac{n_1}{s_o} + \frac{n_2}{s_i} = \frac{n_2 - n_1}{R} \,\text{thin lens formula}$$ for a single lens emerged in medium $n_2$ in the ...
3
votes
1answer
219 views

How deep is the well, given this data?

A rock is dropped into a well. A timer starts when the rock is dropped and is stopped when the noise of the rock hitting the ground of the well is heard. How deep is the well? Here's what I have so ...
2
votes
1answer
614 views
1
vote
1answer
240 views

Finding the electric field on a point (x,y,z) using Coulomb's Law

Using Gauss' Law, the answer is $$\frac{Q}{4 \pi \epsilon R^2}.$$ However if I were to do the integration using Coulomb's Law, I get $$ \int_0^{2\pi} \int_{0}^{\pi}\int_r^a \frac{\rho \sin\theta dR ...
8
votes
9answers
10k views

What's the core difference between the electric and magnetic forces?

I require only a simple answer. One sentence is enough... (It's for high school physics)
1
vote
1answer
785 views

Finding the Electric Field (and other information, besides)

The problem I am working on is: Two parallel plates having charges of equal magnitude but opposite sign are separated by 29.0 cm. Each plate has a surface charge density of 33.0 nC/m2. A proton is ...
5
votes
3answers
1k views

Why isn't average speed equal to displacement over time?

I'm in an introductory Physics course and I need help! During a one-hour trip, a small boat travels 80.0km north and then travels 60.0km east. What is the boat's average speed during the one-hour ...
5
votes
2answers
331 views

Technical detail in the solution of the hydrogen atom

I'm trying to do an exercise in which you solve the Schrödinger equation for the hydrogen atom. Through the exercise, I've already shown that the wavefunction is: $$ \psi_{n\ell m}(r,\theta,\varphi) ...
0
votes
1answer
181 views

What is the momentum of these emitted photons?

5 x 10^7 kg of radioactive material emits energy in the form of photons of red light (700 nm). (Note: photons have no mass.) What is the momentum of each photon? ...
4
votes
1answer
876 views

Infinite-range 1D Ising model + Hubbard-Stratonovich-Transformation

I have a probably quite simple question RE the HST. After some work, I obtain as the partition function for the infinite range 1D Ising model $$Z = \int_{-\infty}^\infty \frac{dy}{\sqrt{2\pi / ...
1
vote
1answer
87 views

Mean value of the force in a collision problem

I have the following problem: A point with mass $m$ and speed $v$ collides with a fixed obstacle and penetrates it, stopping in a space $\Delta x$. Calculate $\Delta t $. I understand the way my ...
-1
votes
1answer
383 views

Internal forces in a truss and its geometry

I'm to work out the internal forces in a truss, but I can't get my head around the geometry of the truss itself. I'm starting to think there may have been information on the diagram which I missed. ...
0
votes
1answer
189 views

Component of force field tangent to a curve

I recently had to solve the following problem: A force $F=10\hat x- 8\hat y$ is applied to an object that is constrained to travel towards increasing values of x along the path defined by $y=x^2$ ...
1
vote
1answer
252 views

Shift operator (integral calculus involving Hermite polynomials) [closed]

I didn't know whether to pose this question on Physics.stackexchange or Math.stackexchange. But since this is the last step of a development involving the eigenfunctions of an Harmonic oscillator and ...
0
votes
0answers
117 views

Number of microstates of discretized paths

Let us consider a square grid, which has been rotated by 45deg. On this grid we define a path, the directed polymer, which starts at the origin ($t = 0$) and extends in the positive $t$-direction ...
0
votes
2answers
1k views

How much work is done when pushing against a brick wall?

So this is one of the questions on my physics assessment and I would like to know how to calculate how much work is done when pushing against a brick wall. My teacher has told me the calculation is: ...
1
vote
0answers
235 views

Computing with qubits [closed]

We have a qubit in the state $|\psi \rangle= √3/2 |0\rangle + 1/2 |1\rangle$, which we want to measure in the $cos \theta\ |\theta\rangle + sin \theta |1\rangle, sin \theta |\theta\rangle - cos θ ...
3
votes
2answers
391 views

Metric coefficients in rotating coordinates

Let $(t,x,y,z)$ be the standard coordinates on $\mathbb{R}^4$ and consider the Minkowski metric $$ds^2 = -dt^2+dx^2+dy^2+dz^2.$$ I am trying to compute the metric coefficients under the change of ...
1
vote
0answers
21 views

Kingston corners [closed]

It is approximately 275km from WVWHS to Kingston corners. If your car gets 30.0 miles per gallon and gas costs 3.85 per gallon, how many cents of gas is burned from going from school to Kingston ...
1
vote
2answers
168 views

Additional mass of block on inclined plane

I would like some help in solving this problem. Height is 15 cm , base is 88 cm My attempt: $$(119.3 + m)(\sin(\theta)) = (88*9.8)$$ $$ 15^2 + 88^2 = 89.269^2 $$ $$ \sin^{-1} = 15/89.269 $$ $$ ...
1
vote
0answers
143 views

Plane vector problem [closed]

Problem statement A jet is flying at 600 mi/h in a direction of 450 North of West. 2.5 minutes later it is flying at 450 mi/h in a direction of 300 North of East. a) Sketch a vector ...
3
votes
1answer
265 views

Find the Hamiltonian given $\dot p$ and $\dot q$

I have these equations: $$\dot p=ap+bq,$$ $$\dot q=cp+dq,$$ and I have to find the conditions such as the equations are canonical. Then, I have to find the Hamiltonian $H$. To answer to the first ...
-1
votes
1answer
358 views

Find generating function $F_1$ for canonical trasformation

I'd like to know the steps to follow to find the generating function $F_1(q,Q)$ given a canonical transformation. For example, considering the transformation $$q=Q^{1/2}e^{-P}$$ $$p=Q^{1/2}e^P$$ ...
0
votes
1answer
117 views

Is it necessary to know initial y velocity to solve this projectile motion problem?

A marble is launched horizontally off a 93.0-cm high table causing the marble to land on the floor 1.85 m from the base of the table. a.) How long was the ball in the air? b.) With what ...