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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19 views

How to determine the direction of acceleration for block A and man? [closed]

My confusion is how to determine the direction of acceleration of block and man. I know that in the same direction. acceleration of Man wrt rope/block will be Acceleration of Man minus Acceleration ...
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63 views

Conserved quantities of a simple Lagrangian

Suppose the following Lagrangian with 2 degrees of freedom: $$L = \frac{3}{2}\dot{q}^2_{1} \ + \frac{3}{2}\dot{q}^2_{2} \ + \dot{q}_{1}\dot{q}_{2}$$ My aim is to find all the conserved quantities of ...
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54 views

Show for $r \in \mathbb R$, $e^{(a_1 ^\dagger a_2^\dagger - a_1a_2)r}|0,0 \rangle = \frac{1}{\cosh r} \sum_{j=0}^\infty (\tanh r)^j |j,j \rangle$

Let $ a_1, a_2 $ be annihilation operators for the first and second component in the product state $|m,n \rangle$ using Fock basis. Following "Quantum continuous variables, A primer of Theoretical ...
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Determining whether I hit the bed when jumping from a cliff [closed]

For simplicity, assume a perfectly spherical object with uniform density falling from some height to a lake. How can I determine whether I hit the bed of the lake? Maybe this has something to do with ...
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28 views

Relation between current (not at saturation) and voltage in photoelectric effect

This is the question I got for an assignment. How do I determine stopping potential from this data? I can see that the relation between $V$ and $I$ seems to be linear, so can I just use the equation ...
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31 views

The exact location of normal force and friction vectors [on hold]

I am struggling with a following question: "A cylinder of radius $r$ and height $h$ is standing on an inclined plane pitched at an angle $\theta$ to the ground. Given the coefficient of friction $\mu$ ...
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35 views

Please check my problem about SI prefixes [closed]

2.2 A single logic gate in a prototype integrated circuit is found to be capable of switching from the “on” state to the “off” state in 12 ps. This corresponds to: (a) 1.2 ns; (b) 120 ns; (c) 1200 ns; ...
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33 views

Change of variable in 4D space-time

I was reading Sidney Coleman's article "Fate of the false vacuum: Samiclassical theory" and i stumbled upon a change of variables that i can't seem to prove. The problem is this: trying to solve the ...
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Why the sum of deformations in given figure is zero?

When a vertical block is kept between two fixed support and when the bottom support is removed, it has the possibility of facing a deformation downwards which was impeded by the upward reaction force ...
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23 views

Toilet Paper roll [closed]

Why we don't replace R in formula (RT=(1/2)m(R2+r2)(a/R)) into (R,outer diameter +r,inner diameter)? Does the inner roll also rotate?
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42 views

Inverted pendulum, EOM

Consider the inverted pendulum shown below: where $F$ is an external force, $B$ is the CoM of the rod, $A$ is the position of the joint where the rod attaches to the car. Angles increase in the ...
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external pressure vs internal volume plot of 1. expanding and 2. contracting cylinder-piston-gas system that obeys Boyle's law [closed]

A gas which follows Boyle's law, is enclosed inside a standard piston-cylinder system having volume V and pressure P. If an external pressure is applied to that massless piston to 1. slowly compress ...
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28 views

How to solve for stable/unstable equilibrium in this question [closed]

A solid cube of side b is at rest on curved surface of a cylinder(horizontal axis) of radius R. Assume no slipping. We have to derive condition for stable equilibrium. My approach: Slightly we can ...
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Can someone explain these circled points…?

Why is direction of friction in the direction of motion and here it is the platform that moves....the movement is not caused by friction so how is friction doing work? In the second one there is no ...
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1answer
80 views

How can i obtain the correction to the eigenvalues as a result of adding the gravitational potential to the hydrogenlike atom?

In treating the hydrogen-like atoms, we normally neglect the gravitational potential for the system. I am able to justify the above statement by comparing the gravitational potential to the ...
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30 views

What will be the equation of the path of spider? [closed]

A cobweb thread of negligible relaxed length is traced between points A and B on two opposite walls as shown in the figure. In this state the thread makes an angle $\theta$ with the horizontal and ...
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12 views

Factors effecting amplitude of damped spring

Let say we have a spring under simple harmonic motion. What are the independent variables that effect the time taken to reach half the initial amplitude during damping? I am guessing a few would be ...
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39 views

What's the shortest “safe” distance from a neutron star merger?

Take GW170817 for example, the first neutron star collision picked up by LIGO. Given how much data we got from that event, can anyone figure out what the "blast radius" is, and how far away from the ...
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15 views

Analysing a lift moving up with acceleration from the inertial frame of the ground

A frictionless inclined plane,making angle $ θ$ with the horizontal, of length $ L $ (inclined plane is a right-angled triangle, $ L$ is length of hypotenuse) is kept in a lift which is moving up with ...
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34 views

A tug of war with different forces at each end of the rope [closed]

If a man pulls a rope with a force of 150N towards him and the other end of the rope is pulled by a small girl with a force of 50N towards her. Assuming rope to be massless. Find tension in the string....
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How am I supposed to get this answer? [closed]

This question is from the Oxford Physics book, and I didn't understand how to get the answer. I'm assuming that the equation that I'm supposed to use E=mc^2 to solve the equation.
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1answer
111 views

Which wave function should I adopt?

Suppose I have Hamiltonian $H_0(\hat{p},\hat{r})$, it satisfies $H_0\psi(p,r)=E(p)\psi(p,r)$. If I make a change from $\hat{p}\to\hat{p}+p_0$, what is the form of the wave function of the Hamiltonian $...
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2answers
76 views

Calculate escape velocity without using energy? [on hold]

Is it practically doable to calculate the escape velocity on the earth not by using the principle of energy conservation, but by calculating the velocity of the particle as a function of time using ...
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The problem was found in the book of mechanics by Kleppner and Kolenkow [closed]

If you start a coin rolling on a table with care, you can make it roll in a circle. The coin leans inward, with axis tilted. The radius of the coin is 'b' the radius of the circle it follows is R and ...
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Energy with dipole [closed]

What is the energy required to rotate an electrical dipole of $q=2e$ and $l=1.5$ nm by 50 degree when it is placed in a uniform electric field that has a magnitude of $45.2$ N/C?
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Divergence of a Vector Field - Surprising Result [duplicate]

I'm following the text Introduction to Electrodynamics by Griffiths, and I came across the following in an in-text problem: Sketch the vector function v = $\frac{\boldsymbol{\hat{\mathbf{r}}}}{r^2}$...
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38 views

Energy Eigenvalues from a given Hamiltonian [closed]

Consider the Hamiltonian, H=σX Where σ=(σx, σy, σz) is the Pauli Vector with the respective Pauli Matrices and X=(x,y,z) is the position vector. What will be the Energy Eigenvalues for the given ...
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Kinematics of a Rigid Body; Thin plate rotated about a point [closed]

I need help with this setting up this equation. So far I have after taking the moment about $O$: $$100(1-e^{-0.4t})-0.75mg\sin{\theta}= \left[\left(\frac{1}{12}m(l^{2}+l^{2})\right)+md^{2}\right]\...
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Pipe pressure drop question [closed]

Water at $20^\circ$C is flowing at $0.1$ cm s$^{-1}$ in a $5$ cm diameter pipe. If the pipe has an equivalent length of 10 m what pressure drop would be expected? Comment on any assumptions made. Is ...
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31 views

Find Pressure applied given compressibility and change in volume [closed]

The volume of a body decreases by $0.001\%$. If the compressibility is $1 \times 10^ {-5}$, then find the pressure applied.
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Bernoulli (?) question? [closed]

can you help me to solve this problem? I have a pipe with water, at a constant pressure of 10 bar. I have then 3 holes, each one of different size and on an orizontal level. Out of which hole does ...
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Physical Interpretation of an Overdamped Pendulum

Consider a damped pendulum whose equation of motion is given in general by $$m\ddot{x}=-\mu\dot{x}-kx$$ where $\mu,k>0$ Rewrite this equation as $$\ddot{x}+2\gamma\dot{x}+\omega^2x=0,$$ where $...
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1answer
42 views

Work Done and Potential Energy in Electrostatics

This is a question from class 12 Physics NCERT Part 1: I am having so much trouble with this, I can't figure out where I'm going wrong. I solved part (a) here: (a) U= -27.2 eV (b) Here, the kinetic ...
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25 views

mass m on a inclined plane [closed]

If the figure shows a smooth inclined plane what should be the minimum magnitude of acceleration which the mass m dropped freely vertically to the ground.
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27 views

How to solve the following problem of particle dynamics involving Hooke's law? [closed]

I cannot solve the problem below: A particle hangs at rest at the end of an elastic string whose unstretched length is $a$. In the position of equilibrium,the length of the string is $b$ and $2\pi/...
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38 views

Motion in Uniform Magnetic Field

Sorry for asking an exercise question here, but I'm really having difficulty figuring this one out. Quick summary of the problem: a charged particle moving in a uniform magnetic field will experience ...
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45 views

A Simple RC Circuit [closed]

This is the most simple Rc circuit (i have just started learning) .My questions regarding this is- (This is a dc voltage supply) Will capacitor get charged by the potential drop of resistor or ...
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26 views

Vacuum restructuring for superconductivity

I have posted several questions about superconductivity recently and all of them are related to vertex function but these questions were incorrect. I have found the following statement in book ...
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1answer
70 views

A doubt in a question of mechanics [closed]

Question: A mass of 2 kg is when kept on a ground,the ground yields steadily and the block goes down with an acceleration of 1 $m/s^2$. Find the reaction force on the block by the ground. I know ...
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54 views

Taylor expansions giving different answers before and after applying Euler-Lagrange equation

I have the Lagrangian $$\alpha(\boldsymbol{\dot{r}} -\boldsymbol{v}(\boldsymbol{r}))^{2} + \beta \nabla \cdot \boldsymbol{v}(\boldsymbol{r}),\tag{1}$$ where $\boldsymbol{r}$ is the position and $\...
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1answer
51 views

If two hooks support weights on a string across a span, how much weight can it support?

Assume there are two hooks, each rated as able to hold 5 pounds. They are both mounted to a wall, one at the north end of the wall and the other at the south end of the wall. The wall is 10 m long. If ...
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23 views

Wavefunction and associated energies of particle in uniform magnetic field [closed]

I'm trying to find the wavefunction and associated energies of a charged particle in a uniform magnetic field . We have the following hamiltonian: $$ H = \frac{(-i\hbar\nabla -q\vec{A})^2}{2m} $$ ...
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25 views

A form factor problem for high energy electrons

Assuming a uniform charge distribution within a nucleus of radius R=$r_{0}$$A^{1/3}$, show that the form factor for $F(q)$ for high energy electron is given by $$F(q)=\frac{3}{q^2r_0^3A}\left[\frac{\...
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35 views

Young's double-slit in Sound waves [closed]

I am going my physics extended essay and I am stuck in explaining my hypothesis. So I am doing an experiment where I have 2 sound sources emitting specific frequencies and I am trying to find fringe (...
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1answer
40 views

What's wrong in my approach towards solving this problem?

This is the problem that I have to solve: The figure shows a block $A$ of mass $6m$ having a smooth semicircular grove of radius $a$ placed on a smooth horizontal surface. A block $B$ of mass $m$ ...
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1answer
63 views

An Evil Vector Problem! [closed]

A person is walking on straight road starting with a velocity $v$, the direction of of air ,observed by him makes an angle $\alpha$ with his is direction of motion. Now during the race, he finds ...
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1answer
103 views

Doubt in quantum mechanics [closed]

My lecturer said that when a oscillating body loses energy in the form of radiation the natural frequency of oscillation is equal to the frequency of the emitted radiation. Can someone explain why?
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1answer
73 views

How can I calculate the equivalent resistance of this circuit with resistors in parallel with wires? [closed]

Problem: Calculate the equivalent resistance, $R_\text{eq} ,$ of this circuit: $\hspace{50px}$. My solution attempt Тhe $12 \, \Omega$ resistor and the $6\, \Omega$ resistor are in parallel, ...
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52 views

How would I calculate the gravity on the surface of a large rectangular solid? [closed]

This story on Reddit involves a 1 km by 1 km by 1.79 lightyear block of lead in deep space, and I was wondering if it was at all feasible (though that question is probably out of scope). To ask a more ...
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1answer
83 views

Energy eigenvalue with Potential $-e^2/ x$

If I have potential which are very well-known like, square barrier, or square well, or step potential, What I do is to set the boundary conditions in Schrödinger's equations. Sometime, the ground ...