Questions tagged [homework-and-exercises]
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.
23,433
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What are the hermitian operators in cylinderical coordinates?
In cylindrical coordinates which of the below are hermitian.
1/i*(ծ/ծs)
1/i*(ծ/ծs+1/s)
1/i*(ծ/ծs+1/2s)
(ծ/ծs+1/s)
the answer says "3" but i don't understand how. The difference in option &...
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0
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13
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How fast would you need to go for five years to become roughly half an hour in relative time?
I'm trying to write a story involving time dilation (came up with it before Lightyear）and one plot point is that an important character was missing for five years, but to them, only a little while had ...
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18
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Translational Equilibrium
The diagram shows two possible choices for a multiple choice question that I used from a test bank. My gut tells me that the answer is B, but I am unable to come up with an explanation as to why ...
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0
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0
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17
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Angular velocity of a physical pendulum [closed]
I'm having trouble solving this problem:
"A pendulum consists of a rod of length 2 m and mass 3 kg connected to the bottom of a solid sphere of mass 1 kg and radius 0.3 m. The axis of rotation ...
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-1
votes
1
answer
47
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Acceleration due to gravity having non uniform density of a solid sphere [closed]
A solid sphere of mass M and radius R has a non uniform density in such a way that the density is proportional to r² at a distance r from the centre. Find acceleration due to gravity at a distance r ...
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0
answers
16
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Electrostatic force between two Non-conducting spheres that are close [closed]
I wanted to find the electrostatic force between two spheres with radius $R_1$, $R_2$, and charge density $\rho_1$, $\rho_2$, and the distance between them is $R$. Also, $R_1$, $R_2$, and $R$ are all ...
0
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0
answers
12
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Poynting vector on a rotating cylinder [closed]
A long cylinder of radius $R$ has a surface charge density of $\sigma$. An externally applied torque causes the cylinder to rotate with a constant angular acceleration: $\omega = \alpha t$ about the ...
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0
votes
2
answers
85
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Finding the Expectation Value of Position for Generic $|n\rangle$ State
For a homework problem I had to write the position and impulse operators in terms of the creation and annihilation operators. The result is as follows:
$$\hat{x} = \sqrt{\frac{\hbar}{2 m \omega }} (a +...
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-1
votes
0
answers
42
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How can i find the electric field? [closed]
A square area of edge length L is located in the XY-plane and centered at the origin. This area is filled with
a uniform surface charge of 10-4 C/m2.
• Find the electric field (magnitude and direction)...
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votes
0
answers
28
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Tangential Velocity of a Wheel Connected to a Rigid Link While Passing the Ramp [closed]
As seen in the figure, the rigid link moves at constant velocity (V) on the x-axis. This rigid link is connected to the tractor on the x-axis from one end and to the wheel from the other end with ...
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votes
0
answers
31
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Centre of mass (two mass block and spring problem) [closed]
Consider the situation of the previous problem. Suppose the block of mass m1 pulled by a constant force f1 and the other block is pulled by a constant force F2. Find the maximum elongation that the ...
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0
votes
0
answers
43
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Trajectory Equation for Pitched Baseball [closed]
I am working with a [NASA Curveball simulator] (https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/ballkiosk/) and am trying to come up with equations to match its results. Unfortunately, [NASAs ...
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1
answer
62
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How to find the optical path difference between two non-parallel light rays?
Consider this Thin Film Interference diagram here.
The Optical Path Difference (${OPD}$) between the reflected light rays from ${C}$ and ${A}$ is
$$OPD = n_{2}({AB} + {BC}) - n_{1}{AD}.$$
I can ...
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0
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32
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AC Node analysis [closed]
i want to ask about the concept of ac anlysis
in the following question,i want to find the value of Vc
here is the soluion
Here is the equation to find out the value of Vc
I know i1+i2+i3=0
in the ...
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votes
1
answer
31
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Difference between friction force and force because of friction?
I'm doing some physics studying right now and the wording of an example question really confused me so I was hoping to get help in figuring it out. It says that " The coefficient of friction ...
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0
answers
55
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Explicit Form of Feynman Propagator for a Scalar Field in Position-space: Derivation Details
This is Problem (6.1) from Schwartz's QFT and the Standard Model. I am trying to directly calculate, by performing the integral over momenta, the explicit position-space expression of the Feynman ...
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-1
votes
0
answers
34
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Capillary Rise and Orientation of the beaker
When a capillary is dipped vertically inside a liquid, the liquid rises upto a height $h$. In the same capillary, the same liquid is filled in horizontal position, then it is kept in a vertical ...
0
votes
2
answers
47
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Confusion in calculation of power [duplicate]
Question-
Sand is being dropped from a stationary dropper at a rate of 0.5 kg s$^{-1}$ on a conveyor belt moving with a velocity of 5 ms¹. The power needed to keep belt moving with the same velocity ...
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votes
0
answers
26
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Quantum mechanics Synchronous Oscillator [closed]
Consider the harmonic oscillator of pregnancy (with electric charge) in the external constant electric field Ɛ , which is given by the following Hamiltonian:
$$H=p^2/2m+1/2(mw^2x^2)-qxƐ$$
In any way ...
-1
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0
answers
22
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At absolute zero temperature when $E$ is equal to Fermi energy $E_f$ at $t=0$ then Fermi direction probability distribution function will be______? [closed]
How you can explain it properly with proper derivation
-1
votes
1
answer
79
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Linear Momentum conservation [closed]
Take a 1kg point mass at the end of a 1 meter massless rod, free to rotate about a pivot at the other end of the rod. If I apply 1 unit of force to the point mass at a right angle to the rod, the ...
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2
votes
1
answer
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3-dimensional 3-state Potts model critical temperature
I was given that the free energy per lattice site of the 3-dimensional 3-state Potts model in the mean field approximation is
$$f\equiv \frac{F}{\text{# sites}} = \sum_{k=0}^{2}(-3Kx_k^2 + \frac{1}{\...
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0
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29
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What will happen if we change all the resistances in an infinite resistance ladder to their double value? [closed]
Let's have a circuit as below:
If the equivalent resistance of above circuit is $Z$ and if we have another circuit as below:
And if the equivalent resistance of above circuit is $R$.
Now my question ...
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0
votes
1
answer
29
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What happens when we integrate angular displacement $θ$ (question picture given below)? [closed]
Here I was trying to Solve this question and I thought what if we integrate both $\alpha$ (angular acceleration) and the value we get when we equate torque with Iα. If we do so We get the desired ...
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0
votes
0
answers
15
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Electric flux through spherical gaussian surface due to a charged non conducting cylinder [closed]
I tried integrating the Electric field component and the elemental ring differential area in 2 parts . First when the Elemental ring radius is greater than R and once when Its less the R because the ...
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-1
votes
0
answers
24
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Fresnel's Equation - Area Terms in Power Expression
I have a lecture note about Fresnel Equations and related power ratios of the reflected and refracted rays. But I cannot understand how the area on the boundary is related to the areas of the rays, e....
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0
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0
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16
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Calculating the capacitance [closed]
Two charged identical spherical objects are hung by two threads in a medium from a point and they become balanced at a linear distance from each other. In another medium, their positions remain all ...
0
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0
answers
19
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How can I calculate the approximate air volume to obtain neutral buoyancy per 1 kilo of weight in Salt water? [closed]
I have a solid round object that weighs 5 kilos. I want to calculate how many liters of air in a plastic bottle is needed for neutral buoyancy in sea water.
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1
vote
0
answers
31
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Problem regarding open systems and a compression [closed]
Say we have a cylinder of height $h_0$ and transversal area $S_\perp$ filled with water vapour and covered by diathermic walls, as well as a mobile diathermic piston on the top, which is in contact ...
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1
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0
answers
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External leg correction to 3-point QED Green's function
I am trying to calculate the following diagram to solve the Callan-Symanzik equation for the three-point Green's function (two massless fermions and a photon).
The counterterm to the photon ...
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26
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Projection of an object towards a planet [closed]
An object (of mass m) is projected from outer space with a velocity v, making an angle $\theta$ with the position vector from the centre of a planet of mass M and radius R. The object is at a distance ...
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Momentum and Impulse Sample Question [closed]
Jonathan and Jane are sitting in a sleigh that is at rest on frictionless ice. Jonathan's weight is 800 N, Jane's weight is 600 N, and that of the sleigh is 1000 N. They see a poisonous spider on the ...
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37
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What's the amount of force needed to push a object on a inclined surface with a particular constant velocity? [closed]
Suppose there is no friction and the angle of inclination is $\theta$. We first need to apply a force of $g \sin(theta)$. I know that this will cause it to start moving forward with no acceleration as ...
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1
vote
2
answers
91
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Finding error in Choi matrix calculation which suggests a CP map is not CP
The question
Consider the following linear, trace preserving quantum map over $d \times d$ quantum states $\sigma$,
$$\Phi(\sigma) = \Pi_R \sigma \Pi_R + (1 - \text{Tr}(\Pi_R \sigma)) \frac{\Pi_R}{R}$$...
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0
answers
18
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Circular motion string at highest point [closed]
So why is the tension in the string at the top most point of a circular motion equal to zero ?
-2
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2
answers
47
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What is the moment of inertia of an I-beam? [closed]
A thin rod of length L and mass m, perpendicular to the axis of rotation, rotating about its center. Its moment of inertia would be $I=(1/12)mL^2$ (see picture). If I want to use an I-beam instead of ...
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0
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14
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Problem of optic [closed]
i need help with a problem and idk how do it, please if someone can help me gonna be great, i want learn how do this problem
Certainly, here's the translation of the problem into English:
Problem of ...
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1
answer
49
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Clarification Needed for The Klein-Gordon Field Acting on the Vacuum State (Peskin and Schroeder)
In Peskin and Schroesder's Introduction to Quantum Field Theory, section 2.3, the Klein Gordon Field has the expression
$$
\phi(x,t) := \int \frac{d^{3}p}{(2\pi)^{3}} \frac{1}{\sqrt{2\omega_{p}}} [a_{...
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0
answers
20
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Newtons Law of Cooling with a coupled system of equations [closed]
I am working on a problem that involves using newtons law of cooling as a coupled system of equations.
Im asked to find the equilibrium temperature of the system, when T(0)=7, and B(0)=3, and state ...
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0
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24
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Differing answers from Kinematics and Law of Conservation of energy [closed]
So I was doing a problem that read:
Given a block of mass m sliding on a horizontal frictionless surface runs into a spring with a spring constant k, and comes to a stop after a distance x, what is ...
0
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0
answers
61
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Relativistic particle inside a moving relativistic frame [closed]
Special Relativity problem:
In the laboratory frame, a particle at rest starts moving with a speed $c/2$ from one corner of a square (see figure) and traverses the four sides of the square so that it ...
1
vote
1
answer
63
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Order of magnitude of $v=\sqrt{q^2/Mr}$
I'm developing a problem and already found the solution, I know is correct to assume in my problem that the velocity of an electron is:
$$v=\sqrt{\frac{q^2}{Mr}},$$
where $q$ is the charge of the ...
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3
votes
3
answers
386
views
Conceptual misunderstanding in Buoyant forces [closed]
This is the problem:A piece of ice floats in a vessel with water above which a layer of a lighter oil is poured.
How will the level of the interface change after the whole of ice melts? What will be ...
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0
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26
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What was Grant Holloways top speed in his 12.81s 110m hurdle run using kinematics? [closed]
I am a currently a introductory biophysics student and I am attempting to analyze Grant Holloway's 12.81s 110m hurdle run. I thought the best approach would be to break the run into stages due to the ...
0
votes
1
answer
64
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Pendulum equation [duplicate]
idk if that kind of question is allowed here, if not, my bad. i alway seen the massless pendulum equation, where at end of all deduction you have something like
$$\frac{d^2\theta}{dt^2}+\frac{g}{L}\...
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0
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Small Oscillations aproximation for gravitational potential in cartesian coordinates [closed]
Hi I have a question concerning the following problem, where masses 1 and 2 slide frictionless on the x axis, while mass 3 hangs from two springs connected with the other two (only the horizontal ...
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0
answers
43
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Calculating eigenvalues symbolically [closed]
I'm reviewing this paper and towards the end I came across this problem and I have no idea how to solve it properly. I constructed the matrix $M$ and calculated the eigenvalues as;
\begin{equation}
M =...
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0
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How to do this question? [closed]
From a solid sphere of mass $M$ and radius $R$, a smaller solid sphere is cut with its diameter as the radius of the bigger sphere. Calculate gravitational field at the centre of hole due to remaining ...
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0
answers
46
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Verification of Electric Field from Infinite Line Charge [closed]
Problem:
I am currently tackling a problem involving the derivation of the electric field $\mathbf{E}$ at location $(0,y)$ induced by an infinite homogeneous line charge $\lambda$ (refer to the ...
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0
answers
37
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How does normal force play a role in this equation? [closed]
While searching online, I found the question.
A uniform rod of mass 30. kg and length 4.0 m is supported from underneath at its left end and at a point a distance of 0.80 m from the middle. Calculate ...
