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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1answer
58 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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1answer
56 views

Calculate escape velocity without using energy?

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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0answers
23 views

The problem was found in the book of mechanics by Kleppner and Kolenkow [on hold]

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 ...
2
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2answers
76 views

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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0answers
35 views

Energy Eigenvalues from a given Hamiltonian

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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34 views

A bead of mass moves with constant speed $v$ along a thin and smooth wire bent to form a curve defined as $y=(0.5/m)x^2$ [on hold]

A bead of mass $m$ moves with constant speed $v'$ along a thin and smooth wire bent to form a curve defined as y=(0.5 m^-1)x^2.The wire lies in horizontal plane.The impulse imparted on the bead while ...
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0answers
21 views

Kinematics of a Rigid Body; Thin plate rotated about a point

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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26 views

Pipe pressure drop question [on hold]

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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0answers
28 views

Find Pressure applied given compressibility and change in volume [on hold]

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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20 views

Bernoulli (?) question? [on hold]

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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8answers
754 views

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
41 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 [on hold]

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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25 views

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

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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0answers
34 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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0answers
40 views

A Simple RC Circuit [on hold]

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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0answers
14 views

Kinetic energy of daughter nuclei after decay given the Q value [on hold]

Assume that we know the Q value of the decay ${}^{230}_{90}\rm{Th}\rightarrow {}^{226}_{88}\rm{Ra} + \alpha$, and we make the simplification that the total mass of a nucleus is the number of nucleons ...
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0answers
23 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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0answers
57 views

How Do I solve Newton’s law of gravity problem? $F = G (M1 * M2) / r^2$ [on hold]

I have been give this problem: F=(6.67∗10−11 (Nm^2/kg^2)) ∗ ((5.64∗1024kg) (1.99∗1031kg)) / (1.51∗1015∗m)^2 I do not understand (Nm^2/kg^2) but I do understand everything else
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1answer
67 views

A doubt in a question of mechanics [on hold]

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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0answers
12 views

MOSFET I - Vg curve [on hold]

Below graph shows the I - Vg curve in the subthreshold region, Quadritica region, and linear region for 5 different transistors. I was asked to determine which I - Vg curve in the below graph is ...
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0answers
12 views

Circular Motion and Force [on hold]

The maximum breaking strength of a piece of cord is 250 N. What is the maximum rpm at which the line can retain a 3 kg mass swung in a 1.8 m radius circle?
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18 views

Speed of Transverse wave and frequency in sitar wire [on hold]

I have a problem to solve though i am not clear on concept. I know, $V = C (T/m)^{1/2}$ Where $C$ is constant, $T$ is tension , $m$ is mass per unit length. Here is the problem A sitar wire in ...
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0answers
16 views

MOSFET Band Diagram from surface to substrate [on hold]

The question below asks to identify the band diagram of MOSFET at different Vg. This band diagram is drawn from oxide-silicon surface to silicon substrate. my understanding is that the band diagram ...
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0answers
25 views

What force per unit of length does each line charge exert on the other? [on hold]

What force per unit of length does each line charge exert on the other? I have Two identical uniform line charges that are $d=0.8\,\rm m$ apart. They are parallel to the z axis. They have an ...
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0answers
10 views

$C$-$V$ characteristics of MOS capacitors for different material [on hold]

For C-V curve below for 3 different materials, (Si, InAs, InSb). What material will be corresponding to curve A/B/C? My understanding is that C is inversely proportional to the dielectric constant in ...
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0answers
13 views

P-I-N Semi-Conductor Cell Efficiency [on hold]

I am working on this home work problem (See graph below), asking which curve I/V has higher efficiency. Question 1 : My understanding is that cell efficiency is related to Isc * Voc * n, How could I ...
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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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0answers
22 views

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

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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0answers
32 views

Young's double-slit in Sound waves [on hold]

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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0answers
33 views

Find the maximum amplitude of oscillation of the spring mass system [on hold]

A platform of mass m is supported by a spring of force constant k as shown. When the platform is slightly pressed and released, it performs simple harmonic motion. Find the maximum amplitude of ...
1
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1answer
34 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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0answers
24 views

Work done In equipotential surface [on hold]

ABCD is an equipotential surface. Point P1 and P2 are on the surface and P3 is on a line perpendicular to P1. what is the work done to displace a test charge from p1 to p3
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1answer
59 views

An Evil Vector Problem! [on hold]

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 ...
-1
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1answer
101 views

Doubt in quantum mechanics

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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0answers
28 views

Linear and rotational forces [on hold]

Given a solid body accelerated by gravity, in contact with a cylinder of radius $r$, whose axis cannot translate, how to account for the forces acting on both? Assume the mass of the solid is 1 kg ...
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1answer
71 views

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

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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0answers
51 views

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

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 ...
1
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1answer
81 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 ...
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0answers
17 views

Mathematically modelling the non-planar double inverted pendulum

Using Lagrangian mechanics, how would I go about trying to model the double inverted pendulum that can swing out of plane. A lot of existing work has been done on the planar double inverted pendulum. ...
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0answers
22 views

Finding magnetic flux density of a point a certain distance away from the curved face of a disc magnet [on hold]

I have used this website here because I am trying to find a formula that will tell me the magnetic field strength (B) of a point a certain distance away from the curved part/round face of a circular/...
3
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1answer
65 views

Symmetry of the hamiltonian $H = \frac{1}{2m}p^2 + V(r) + a \, \vec{s} \cdot \vec{l} $

Consider the hamiltonian \begin{align} H& = H_0 + a\, \vec{s} \cdot \vec{l} \\& = \frac{1}{2m}p^2+ V(r) + a\, \vec{s} \cdot \vec{l}, \end{align} where $V(r)$ denotes an arbitrary central ...
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0answers
43 views

I got the answer but I suppose I did not understand the question very well [duplicate]

See as per the question, The Inductor pretty much will induce emf due to magnetic field and not due to other coil/current nearby. Thus I used $E= - d(phi(t))/dt$ as the induced emf. Then using (...
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1answer
35 views

Understanding distances and unit vectors in this problem

A charge $-q$ is at $x = -a$ and a second charge $+q$ is at $x = a$ Between the charges, the contribution from each charge is in the negative direction. An expression for $${\overrightarrow{E}} = \...
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0answers
30 views

How hard is it to lift a car? [duplicate]

You have a car and would like to lift one side (so that two of the wheels don't lay on the ground). How hard would that be? I am talking about a car close to the average dimensions: 1200kg, 4m20(...
0
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1answer
58 views

Solid in Liquid Heat Transfer (Temperatures/Entropy Changes)

Suppose we have a solid of temperature $T_s$ and heat capacity $C_p$ submerged into a pool of water that has temperature $T_w$. If $T_s \gt T_w$ and the pressure of the isolated pool-solid system is ...
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2answers
36 views

Why can I use conservation of momentum to understand a bag getting dropped on a moving truck, if the ground provides an external force?

Please help me with this sat question from released test A toy truck with a mass of $0.6$ kg initially coasts horizontally at a speed of $2$ meters per second. A child drops a beanbag with a mass ...
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0answers
23 views

Central force fields [closed]

A particle of mass m moves In a central force field given in magnitude by f(r)= -Kr, where k is a positive constant,if the particle starts at r=a,theta=0, with a speed v in a direction perpendicular ...
0
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1answer
62 views

Normalizing a set of eigenfunctions with different domains [on hold]

Maybe it seems so easy, but it is not! How can we obtain the normalization constant $N$ for a set of eigenfunctions with different domains? For example, we have $\psi_{1}=N(f_{1}e^{-\kappa x}+g_{...