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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.

0
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2answers
29 views

Magnetic field of long cylindrical wire

i have been studying electromagnetism on my own and I got a question about an exercise in David Griffiths, Introduction to Electrodynamics book. So I'm asked to calculate the magnetic field both ...
0
votes
1answer
29 views

A circular motion problem

A car goes on a horizontal circular road of radius $R$, the speed increasing at a constant rate $\frac{dv}{dt}=a(constant)$. The friction coefficient of the tyre is $\mu$. Find the speed at which the ...
-1
votes
1answer
49 views

Proof for $\langle i[A,B]\rangle$

I have to prove the following equation: $$ \langle i[A,B]\rangle = 2\mathfrak{Im}\left[\int dV(\overline{B\psi)}(A\psi)\right]\,,$$ where A,B are hermitian operators. Here is my calculation, but I don'...
0
votes
1answer
19 views

Qualitative Argument in a Projectile Motion Question

Essentially, my qualms are with Part (a). The argument I’ve come up with are as follows: The ball was launched perpendicular to the plane. That means that the launch angle, which is the angle with ...
-3
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0answers
18 views

Dynamics - Masses on Inclined Planes [on hold]

Calculate the coefficient of friction between the block and the ramp if the block reaches a velocity of 0.45 m/s at the bottom of the ramp. Given values: Block has a mass of 60 kg The inclined plane ...
1
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0answers
23 views

De Sitter spacetime affine parameter

I am reading Chapter 8 in Carroll's "Spacetime and geometry " textbook and I was lead to exercise 8.2, given as: Consider de Sitter space in coordinates where the metric takes the form $$ds^{2} =...
0
votes
1answer
19 views

Formula manipulation [on hold]

What is the potential energy of a metric ton (1000 kilograms), 3 meters above Earth's surface (at sea level), expressed in Kilowatt Hours? Assume that the mass will end travel when it contacts Earth. ...
0
votes
1answer
14 views

Thermal Equilibrium in bucket water with Al piece

Sorry in advance for the poorly formulated title. I am currently going through some assigments in Phyics and came across this one: Question: The heat capacity of a bucket is 1200 J/K and contains 2,...
-1
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0answers
22 views

Acceleration of a pulley [on hold]

In the figure shown, m1=1kg, m2=2kg, m3=0.5kg and m4=4kg. On solving, I observe that the pulley P accelerates downwards. Why does that happen when P has lesser mass hanging from it than Q does? The ...
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0answers
18 views

EM- waves in anisotropic medium

When ElectroMagnetic waves from vacuum enter the anisotropic medium. If the $\epsilon$(permittivity) matrix is diagonal (with not all diagonal entries being equal). There'll be two waves in the ...
0
votes
0answers
20 views

Flux through a cylinder located inside another perpendicular to it's axis [on hold]

A long cylindrical volume contains a uniformly distributed charge of density rho. Find the flux due to the elctric field through the curved surface of thr small cylinder whose axis is OP, and whose ...
0
votes
1answer
44 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
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0answers
33 views

Rain Car problem [on hold]

Rain falls with a speed of $10√2$ m/s. It makes 45° with vertical and 45° with a line drawn towards the north. Find the velocity with which car has to travel in the east direction so that for a person ...
7
votes
1answer
414 views

Escape velocity for Schwarzschild metric

I can't fill in the gaps in my solution to this and assistance or a reference would be appreciated. The question begins with the straightforward derivation of the EoM for a massive particle orbiting ...
0
votes
1answer
1k views

Relative acceleration of bodies on opposite sides of a pulley

This is a problem that I encountered while solving problems related to constrained motion: With all the data given in the above question, I believe that the monkey just holds on to the rope and does ...
0
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0answers
20 views

Young's Double Slit, phase difference and path difference

To produce an interference pattern, the light sources must be coherent right? Coherent by definition means constant phase difference between waves of the same frequency so that means waves can be ...
1
vote
1answer
652 views

What is the effect of volume on liquid temperature during evaporative cooling?

Imagine two evaporative cooling experiments: In the first, a beaker contains a known volume of liquid. The liquid starts at ambient temperature. The temperatue of the body of liquid remaining in the ...
0
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0answers
12 views

Accurate derivation of electron-phonon scattering contribution to metal resistivity

My lecture derived the expression for this contribtuin using the collision integral approach but I missed lot of details. He considers the lowest order correction to distribution function $f=f_0+\...
0
votes
1answer
28 views

Homogeneous cube rotating around its edge

I'm trying to solve the following problem from the book "Analytical Mechanics" by Nivaldo Lemos: Given the cube above, rotating around the edge that coincides with the z axis, find: i) Vector ...
1
vote
1answer
71 views

Time dilation caused by gravity and special relativistic velocity [closed]

I am working on an exercise for my Relativity class. The exercise is: Two atomic clocks are transported in two aeroplanes once around the Earth in either eastern or western direction. For ...
0
votes
0answers
16 views

Bessel differential equation from integral [migrated]

It is a relatively well-known fact that $$\int_{0}^{2\pi}e^{-ikr\cos\theta}d\theta=2\pi J_{0}(kr),$$ where $J_{0}$ is the Bessel function of the first kind and order zero. I'm trying to show that this ...
0
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0answers
8 views

Magnatic flux through a disk with inner and outer radius [on hold]

Hi guys i got this question in my exam today: What is the magnitude of the magnetic flux through the circular loop shown in the figure, containing a uniform B within a region of an area ab. The inner ...
-1
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0answers
19 views

Is Frictional force on each block 3kg or 12kg? [on hold]

Two blocks P and Q of masses m1= 2 kg and m2 = 4 kg are connected to a third block R of mass M as shown in Fig. 3.16 For what maximum value of M will the system be in equilibrium? The frictional force ...
7
votes
1answer
493 views

General motion of a cone on an inclined surface

Suppose that a solid cone is placed horizontally on an inclined surface and is initially at rest. How will the cone move when it starts motion due to its weight? I know that its motion depends on the ...
0
votes
0answers
20 views

Analysis on gamma-ray spectrum [on hold]

I am having trouble with the analysis portion of my experiment. My group has performed gamma-ray spectroscopy on several radio active sources. I am to identify these materials through our analysis. ...
3
votes
1answer
57 views

Circular Orbits Around a Reissner-Nordstrom Black Hole

I'm doing some practice problems on GR and came across this which I'm totally stuck on: The worldline of a photon orbiting a RN black hole is desribed by: \begin{equation} \left(\frac{dr}{d\sigma}\...
0
votes
0answers
18 views

How is the effective mass of electrons related to the specific heat of an electron gas? (in uniform magnetic field)

Just to make it clear, this is related to solid state physics. QUESTION How is the effective mass of electrons in uniform magnetic field related to the specific heat of an electron gas? DETAILS ...
0
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2answers
58 views

Question on using calculus in physics problem [on hold]

I did the following question: A smooth ring of mass $m$ can slide on a fixed horizontal rod. A string tied to the ring passes over a fixed pulley $B$ and carries a block $C$ of mass $M =2m$ as ...
0
votes
3answers
527 views

Current from Middle Battery in a Two-looped Circuit

With this question, as with many tutorials of similar questions I’ve found online, my textbook only mentions three currents: $I_1$, which flows through the left loop from and to the 19 V battery, $I_2$...
0
votes
1answer
30 views

Derivation of gradient of the expectation of local energy

Background: In Variational Monte Carlo, given a Hamiltonian $H$ and a wave function $\psi_\alpha$ dependent on some parameter(s) $\alpha$, we have defined a quantity known as the local energy, $$E_L =...
0
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0answers
10 views

What is the gravitational torque on a square frame?

A rigid wire is in the shape of a square of edge-lenth L, mass m and it carries a current I. The square lies on a flat horizontal surface, with a magnetic field of magnitude B is parallel to two edges ...
1
vote
2answers
60 views

Why is this method of solving this capacitor problem wrong?

The problem was to solve for the capacitance of this system if initial capacitance was C. I solved it using the method which has been given as wrong.My question is that why is potential difference ...
0
votes
1answer
350 views

Coordinate transformation problems

Two questions here, both related to one another. SOLVED Question 1. I am looking to transform a dual vector $p_a$ from spherical polar coordinates to Cartesian coordinates. My dual vector is given ...
3
votes
1answer
101 views

Time evolution of a Gaussian wave packet, why convert to k-space?

I'm trying to do a homework problem where I'm time evolving a Gaussian wave packet with a Hamiltonian of $ \frac{p^{2}}{2m} $ So if I have a Gaussian wave packet given by: $$ \Psi(x) = Ae^{-\alpha x^...
0
votes
0answers
43 views

Light path in a Schwarzschild spacetime

This might be a silly question for the physicist as I'm not one but I've have watched this YouTube video which shows the steps needed to simulate light path in a Schwarzschild spacetime, what I failed ...
0
votes
1answer
19 views

Velocity of a rotating wheel with axle unlocked from wheel vs locked

For a bike wheel rolling down an incline as like the image, initially the axle of the wheel is not locked to the wheel, so the axle rotates as it moves down the incline but the wheel itself possesses ...
0
votes
1answer
464 views

Adiabatic volume change of an ideal gas thought process

I am struggling with trying to solve the following problem, attempting just (a) and the first part of (b) for this exercise: During a reversible adiabatic volume change of an ideal gas, $PV^{\gamma}...
0
votes
1answer
28 views

Properties of Expectation Values Under Variable Substitution

I am working on a homework problem from Griffiths QM (Problem 2.11, 3rd Edition). Specifically, I'm working on finding $\left<x^2\right>$ for the ground state and the first excited state of the ...
0
votes
1answer
62 views

Integration by parts, Weinberg Cosmology p.526

How do I perform this integration by parts done explicitly? $$0 = \delta I_m = \int d^4 \sqrt{-g} T^{\mu \nu} \left[- \frac{\partial \epsilon^\rho}{\partial x^\mu} g_{\nu \rho} - \frac{\partial \...
2
votes
0answers
23 views

Normal force at junction [on hold]

Question is to compare normal forces at A,B and C. I found out theta subtended by arc AB to be $30°$. Problem is at point B. As for a point just before B, normal force is $mg\cos30° + mv^2/100$. But ...
0
votes
0answers
31 views

Gravity and propulsion [on hold]

If a body (m) weighs 200 lbs (90.7185 kg) at sea level and gravity diminishes as the distance between it and the earth (M) increases, what would the body's relative weight be at an altitude of 128,000 ...
1
vote
0answers
16 views

Radius of curvature of a spherical mirror using only magnification?

Given that an object of heigh 1cm is placed in front of a spherical mirror and produces an upright image of height 0.2cm, find the radius of curvature of the mirror. I know that $ M = \frac{h_i}{h_o}...
-1
votes
0answers
22 views

Explain why the angle of incline of the ramp affects friction between the surface of the ramp and the object [on hold]

Experiment: the object is placed on the ramp and the angle between the ramp and the floor is changed.Explain why the angle of incline of the ramp affects friction between the surface of the ramp and ...
0
votes
0answers
21 views

Intensity, power and efficiency question help

The solar Intensity in the Netherlands is $1.0e3\ W/m^2$ at a maximum sunshine and a perpendicular incidence. On average, about $10\%$ of this peak power can be utilized. The efficiency of the ...
0
votes
2answers
29 views

What is Work Done against the Atmosphere

{Assume it's a Spherical Balloon} The answer on the book states (7pV), but I'm definitely missing something. I've looked up online on what 'Workdone against atmosphere' means but there is little to ...
1
vote
0answers
70 views

Earth's surface area

Here we are trying to calculate the earth's surface area via geodetic coordinates: \begin{align} x&=(R\,p(\lambda)+h)\sin\lambda\,\cos\phi\\ y&=(R\,p(\lambda)+h)\sin\lambda\,\sin\phi\\ z&...
1
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0answers
28 views

Electron-positron annihilation into proton-antiproton

How can I obtain the differential cross-section of the process $e^{+}e^{-}\rightarrow \bar{p}p$ from the cross section of $ep$-scattering? I have calculated the amplitude of $ep$-scattering and see $...
0
votes
0answers
9 views

How do Oort's constants relate to shear and vorticity?

I am told to show that Oort's constants represent shear and vorticity in the velocity field of an orbiting star. I know that Oort's constants are defined as: $A = \frac{1}{2}(\frac{v_{\bot,0}}{R_{0}}...
-1
votes
1answer
33 views

Please tell me how to solve star resistance network [on hold]

Please tell me how to solve star resistance network I have tried solving it, but the connection between the crossed resistances is confusing me.
0
votes
1answer
38 views

A pseudo force problem [on hold]

I got the following question in an app, while I was preparing for the exams. A wedge is placed on a smooth horizontal surface. Wedge contains a circular quadrant of radius 25 cm as shown. An insect ...