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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.

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18 views

Determine the mass and radius of colloidal particles through centrifugation [on hold]

This exercise was given to me recently as homework: A centrifuge is used to determine the mass $m$ and radius $R$ of spherical colloidal particles. By rotating the centrifuge at an angular velocity $...
1
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0answers
25 views

Rolling Ball on an Inclined Plane with Spring [on hold]

I would like to solve the following mechanics problem and would like to get few hints. There is an inclined plane with angle $\alpha$. A ball of radius $r$ rolls on the inclined plane that has a ...
-1
votes
1answer
24 views

Oscillating Bar on rollers [on hold]

I'm currently preparing for my exam and am stuck at the following scenario. Suppose we have two rollers rotations against each other and now place a bar on top. The distance between the rollers is $L$...
2
votes
1answer
48 views

$N$ Independent Oscillators Entropy and Number of States

I have been working on building intuition and experience with solving problems related to the microcanonical ensemble, but I haven't been able to solve the following problem: If you have $N$ ...
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1answer
48 views

Quantum Computation - Finding joint state given partial properties of two pairs of qubits [on hold]

I have a problem I need to figure out how to solve for an exam in a few days and I'm struggling to find any advice online I need to find the joint state of two pairs of entangled qubits following the ...
1
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0answers
19 views

Microcanonical Ensemble Entropy of System with Degeneracy

So, I have been trying to find the entropy of the following system as a function of energy: the system consists of N atoms, N much greater than 1. Each atom has three energy levels: the ground state ...
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1answer
8 views

Basic labeling of the hyperfine structure of $^{133}$Cs

I am practicing some questions in preparation for an upcoming exam and the following has me stumped: The D2 line of $^{133}$Cs involves transitions between the ground state $6S_{1/2}$ and the ...
3
votes
1answer
59 views

Why does mass not affect the time and maximum steepness in which an uphill roller rolls?

While investigating the classic mechanical problem of an uphill roller, I realized that the mass of the uphill roller does no affect the steepness of how high the roller can roll and also the time it ...
-2
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0answers
30 views

Question on reflection via plane mirrors [on hold]

two plane mirrors A and B are aligned parallel to each other, as shown in the figure. A light ray is incident at an angle 30 degree at a point just inside one end of A the plane of incidence coincides ...
-1
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0answers
26 views

Electric flux through y-z plane in a dipole [on hold]

A dipole lies on the $x$-axis with positive charge $+q$ at $x=d/2$ and the negative charge $-q$ at $x=-d/2$.find the electric flux $Φ$ through y-z plane placed midway between between the charges. My ...
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1answer
12 views

Finding intensity of laser after round trip in cavity with single mirror [on hold]

I came across a question in a text book today, and was wondering if someone could maybe check to see if my physics and workings are correct, as I am getting a intensity value greater the what going ...
2
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0answers
18 views

Velocity of fluid dividing to two different paths [on hold]

Fluid of density $\rho$ is flowing through a pipe with area $A$ with velocity of $V$. The pipe divides into two different pipes of area $\frac{1}{2}A$ and $\frac{3}{2}A$ with the right end opened. All ...
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3answers
70 views

Divergence, gradient and differentiation - radial irrotational fluid flow

Given a fluid with the steady spherically symmetric flow with only radial velocity $\vec v(r)$. We need to evaluate $ \vec v \cdot \nabla \vec v $. From vector calculus $$ \vec v \cdot \nabla( \vec ...
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votes
1answer
23 views

Number of particles needed when equilibrium energy is given [on hold]

N particles obeying classical statistics are distributed among three states having $\epsilon_0=0$, $\epsilon_1=k_BT$ and $\epsilon_2=2k_BT$. If the total equilibrium energy of the system is $1000k_BT$,...
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0answers
26 views

Designing a potential well [on hold]

Design a potential well in which the probability that the particle in the first excited state can be found in $x \in [-\frac{x_0}{2}, \frac{x_0}{2}]$ is equal to $\frac{1}{2}$.$$$$ So the first ...
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0answers
24 views

How do I use the amplitude of two transmission pulses from different length cables to determine the attenuation of the cable? [on hold]

I need to determine the attenuation of a cable. To do this I took two different measurements using two cables with the same characteristic imedance ($50 \Omega$). One was length $22.93$m and the other ...
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0answers
18 views

Jeans equation for a fully isotropic velocity dispersion tensor

Given a known spherically symmetric gravitational potential, $\Phi(r)$, I need to calculate the value of the velocity dispersion tensor $\sigma_{rr}$. To calculate $\sigma_{rr}$ I am using Jean's ...
-1
votes
0answers
15 views

How to find entropy $s_1$ and $s_2$? [on hold]

Hey guys i am looking thermodynamics chart but i don't find entropy value.Help me guys. How did you find entropy of this question?
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0answers
27 views

Finding the wave function of a particle under varying potential (QM) [on hold]

Given: a particle with mass m is under potential of $$V(x)= \begin{cases}-\frac{A}{x} & \text{for}\ \ x\geq 0 \\ 0 & \text{elsewhere} \end{cases} $$ Show that the wavefunction ...
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1answer
47 views

What is the wavelength of radio waves, if the radiation power is 1kW? [on hold]

The radio station emits every second photons. What is the wavelength of radio waves, if the radiation power is 1kW? So here is what I did: t=1s n= P=1kW= W After that I calculated E=? But ...
-2
votes
1answer
81 views

How do I solve this Laplace equation? [on hold]

I'm stuck with the following problem: Suppose we have an infinitely long box whose cross-section has a rectangular shape of dimensions 2×3. Take the four last digits of your student ID number as a ...
-2
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0answers
21 views

Oscillations and Vibrations [on hold]

Please someone help me solve this question.
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0answers
17 views

Photoelectric effect and emission

How would I calculate the number of electrons emitted from say a given intensity of light. For instance number of electrons emitted per unit time interval (second) in a $\text{mm}^2$ metal surface? ...
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0answers
33 views

The question is given in the image please help me find the solution [on hold]

I'm unable to understand how come the answer is in tan form please help!! The answer given is C. Thank you all in advance for your help
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1answer
11 views

Using RHR for Integration of Amperes Law

My professor breifly mentioned in passing that one can use the RHR for amperian loops such that the thumb is pointing current in any conductor and the fingers and curling in the integration of ...
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1answer
44 views

Is the addition of a Christoffel symbol and the partial derivative of a vector a tensor?

The partial derivative of a vector $V^\lambda , _\nu$ is not a tensor. Neither is a Christoffel symbol $\Gamma^\lambda _{\mu \nu}$. Is the addition of these two objects a tensor? If they were ...
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0answers
90 views

Torque vector: what's up with the signs? [on hold]

I'm trying to calculate the torques produced by the following 4 force vectors: Left: rear view. Right: side view. The figure is not to scale. The positions vectors of the 4 force vectors are: $$\...
1
vote
1answer
41 views

How could I derive the Noether charge for a real scalar field?

I know for a (free) complex scalar field $\psi$ the Lagrangian is: $$ \mathcal{L} = \partial^\mu \psi^\ast\partial_\mu \psi$$ and that Noether's theorem from the $U(1)$ symmetry of the system gives a ...
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0answers
39 views

Force on trapezoidal tank

I'm stuck with this problem that I have almost solved but the last bit seems impenetrable. Please take a look at the problem on the image i provided. Plan: I started by calculating the momentum flow ...
2
votes
2answers
41 views

What is the significance of maximum compression in spring?

A block of mass $m$ sliding on a smooth horizontal surface with a velocity $v$ meets horizontal spring of spring constant $k$ fixed with wall. Find maximum compression of spring. Why is the word ...
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0answers
43 views

Pendulum struck by moving mass [closed]

One of the problems I was given as practice is as follows: I am curious as to how I would approach this problem if perhaps the mass m that strikes the mass M is not approaching at an angle orthogonal ...
0
votes
1answer
52 views

Pendulum general case [closed]

How to prove that the general moviment of a pendulum, considered as point mass suspended from a fixed point with an inextensible rope, is an ellipse? What is the relation between the pendulum's ...
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1answer
31 views

Elastic collision respect to a CM frame [closed]

Two particles, m1 and m2 collide one-dimensionally, if the collision is elastic. show that with respect to the cm frame, the particles reverse their velocity directions, maintaining the magnitudes.
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0answers
34 views

Density of state $g(e)$ Bose-Einstein Condensation system [on hold]

Consider Bose-Einstein condensation of a hypothetical system consisting of N boson particles. The energy of single-particle states is e= eo n^2, where eo is the energy of the ground state and n = 1, ...
-2
votes
0answers
17 views

Using the flux of Bremsstrahlung to analyse medium [closed]

An HII region at a distance of 400 pc is observed to emit thermal Bremsstrahlung across a wide range of radio wavelengths. Independent analysis of emission lines suggests that the characteristic ...
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0answers
26 views

Boundary conditions of spun string

Problem: Consider a string with mass per unit length $\rho$ and length $L$. It is spun about one end, with angular velocity $\omega$ , such that the motion is in a plane (we neglect gravity). Let $x$...
2
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1answer
60 views

Magnitude of vector field [on hold]

I think this is more of a mathematical question, but since it's for a physics problem I decided to ask it here. I have this complicated magnetic field in spherical coordinates $(r, \theta,\phi)$, $$ ...
-2
votes
0answers
28 views

AP Physics Multiple Choice Question [closed]

Three blocks of masses $m$, $3m$, and $2m$ resting on a frictonless horizontal surface are connected to identical ideal springs, as shown above. A force of magnitude $F$ directed to the left is then ...
-1
votes
0answers
63 views

A particle of water is travelling through a cloud [closed]

I remembered one old "Challenge" that my teacher once showed us. It asked us to prove that the acceleration of a particle of water travelling through a cloud is equal to g/7. The M and the V of the ...
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6answers
2k views

Homework question about an engine pulling a train

An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000N , calculate the acceleration of the train. To find the acceleration of ...
-2
votes
0answers
38 views

How can I find $E$-field from $H$-field? [on hold]

I found the answer to this question a little bit confusing I have two doubts 1. What is the first E field [RED UNDERLINED] obtained in the solution 2. From where did [YELLOW HIGHLIGHTED EQUATION] ...
1
vote
2answers
64 views

What is the electric flux through the flat and curved surfaces? [on hold]

My question is from Physics For Scientists And Engineers 7th: A particle with charge Q is located immediately above the center of the flat face of a hemisphere of radius R, as shown in the figure. ...
0
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0answers
38 views

A block and cylinder bodies on a rough inclined plane [on hold]

On a rough inclined plane of inclination 45° a block of mass m and a cylinder of mass 2 m are released Coefficient of friction between all the surfaces of contact is 0.5. If the acceleration of the ...
-1
votes
0answers
36 views

Calculating Magnetic flux through a surface [on hold]

A cylindrical cable (called shell) consists of an insulator up to a radius of $1 cm$ and then a non-magnetic conductive material up to a radius of $1.4cm$. , which carries a current of $50 A$ in the $\...
-2
votes
0answers
15 views

How to calculate shear stress in Cartesian coordinates for two dimension flow? [closed]

I want to calculate shear stress component in $x$ direction for two dimensional flow (Newtonian). Can anyone share and discuss a little bit?
-1
votes
0answers
12 views

Hiw to find net frictional force if the surface in contact are rotating w.r.t. each other [on hold]

A disc of radius R is kept flat on a rough horizontal surface of friction coefficient μ with its axis vertical. It is given an angular velocity ω about its vertical axis and horizontal velocity v(v
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0answers
32 views

Special relativity conceptual doubt [closed]

Suppose a beam of light is fired from an object to a planet while the object is moving away from the planet. Will an observer on the object measure the time taken for the light to reach the planet ...
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0answers
22 views

The precision of a gravitational wave interferometer [on hold]

The latest design of the space-based interferometer LISA will search for gravitational waves using three telescopes separated by arm lengths of 2.5 million km in a triangular configuration. The LISA ...
0
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1answer
33 views

Kinetic Energy Comparison Marble Question

A uniform marble of mass M rolls down a symmetric bowl, starting from rest at the top of the left side. The top of each side is a distance h above the bottom of the bowl. The bowl is rough enough to ...
1
vote
1answer
45 views

Weight and potential energy for a spring pendulum

Consider a spring pendulum like in this figure suppose the spring is arranged to lie in a straight line and its equilibrium lenght is $l$. Consider the unit vectors $e_1, e_2$, $e_x, e_{\...