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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Discuss, in your own words, the phenomenon of standing waves in a stretched string. Explain how standing waves are produced in vibrating string exp.? [closed]

Discuss, in your own words, the phenomenon of standing waves in a stretched string. Explain how standing waves are produced in the vibrating string experiment?
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Unit's conversion

Hey Physices stack exchange I'm new here. I'm doing math project and I've been asked to do some unit conversion but not sure if I'm right. My project is about molecules, I would like to convert all ...
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How to calculate the centroid for this cross section?

Question: A rack is made from roll-formed sheet steel and has the cross section shown. Determine the location $(x, y)$ of the centroid of the cross section. The dimensions are indicated at the center ...
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Calculate magnetic field $B$ in an infinite magnetized sheet

I'm having some trouble when I'm trying to do this exercise: An infinite sheet of parallel faces with thickness $d$ is uniformly magnetized. Its magnetization is 10 A / m and forms an angle of 60º ...
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Expressing this result in different coordinates

Is there a neat way to express this in Cylindrical and Spherical coordinate systems? $(\vec{A}.\nabla)\vec{B}$ Reference: this occurs quite frequently in Electrodynamics books including Griffiths. ...
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I am trying to rearrange the doppler effect equation to solve for $v$ (the speed of sound)

I am given the doppler frequency (Fd), the original source frequency (Fo), the source velocity (Vs) and the observed velocity = 0 (Vo). The question is about a stationary observer with an object ...
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Unknown incorrect step in derivation for pendulum with rotating pivot

Intro/background Consider a massless rod of length $L$ with mass $M$ rotating vertically about a pivot. The pivot is fixed to a circle which is forced to rotate at $ \omega$. Find the Lagrangian. Call ...
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Differences between observations of light versus gravity for a satellite traveling by the sun

A satellite travels in a geodesic by the sun with sufficient velocity to escape the sun's orbit. The distance of closest approach is 100 light seconds when the satellite's velocity is perpendicular ...
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Charging capacitor, with series and parallel resisters

I understand how equations for charging capacitor are derived and what they represent. But here is my problem: if you want to experimentally see how voltage on capacitor changes with time, you have to ...
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1answer
40 views

OPE in linear dilaton theory

I'm trying to do the following question from David Tong's problem sheets on string theory: A theory of a free scalar field has OPE $$\partial X(z)\partial X(w) = \frac{\alpha'}{2}\frac{1}{(z-w)^2}+......
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Newton's law of motion problem [closed]

Attractor pull two carts of equal mass behind it. A rope couples the first cart to the second cart. Ignoring friction, show that when the two carts move with constant acceleration, the tension in the ...
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When direction of rotation of alternator is reversed, why the induced emf will also be reversed?

There is a questio in my textbook: Below show the structure of a bicycle alternator: And the output terminal is connected to CRO to show the induced emf. When the magnet is set to rotated in one ...
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1answer
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Equivalency of conditions involving angular momentum of a rolling ball hitting a wall

(59th Polish Olympiad in Physics) A ball of mass $m$, radius $r$ and a moment of inertia $I = \frac 25 mr^2$ is rolling on the floor without sliding with the linear velocity $v_0$. It hit the wall ...
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$SU(3)$ irreducible representations with tensor method

I am dealing with the tensor product representation of $SU(3)$ and I have some problems in understanding some decomposition. 1) Let's find the irreducible representation of $3\otimes\bar{3}$ we have ...
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1answer
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Forced oscillation resonance frequencies [closed]

Given this forced oscillator: $$ \ddot{x}+\gamma\dot{x}+\omega_0^2x=\frac{F(t)}{m} $$ Where $F(t)$ is: $$ F(t)=\sum_{n=1}^{\infty}\frac{4F_0}{n\pi}\sin\left(\frac{2n\pi t}{T}\right) \hspace{0.4cm} \...
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Electric field lines and Gauss law [closed]

I have found a formula for maximum height attained by any field line which is starting at an angle of “t” between +q and -q separated by a distance of 2L. This height is referred to the maximum ...
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Does autoionization constant stays the same even if we add $\rm HCl$ and $\rm NaOH$ to water? [closed]

In a homework, I am asked to calculate the constant Ka of this reaction: OH- + H3O+ ===> 2H2O (it is a titration of a strong base NAOH with a strong acid HCl) while I don't have the concentrations ...
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What would be the maximum distance we could observe the sun if it had zero bolometric correction?

it is known that the apparent bolometric magnitude of a star at a distance d is given by $$m_{bol} = M_{Bol}\log(d/10pc)\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;(1)$$ where $M_{bol}$ is the ...
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Curl of Magnetic Field in Cartesian Coordinates [duplicate]

I'm struggling to understand why the curl of this magnetic vector field would be zero: $$B(x,y,z)=\left(\frac{-y}{(x^2+y^2)},\frac{x}{(x^2+y^2)},0\right)$$ This cartesian field was derived from the ...
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3answers
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Can the initial wavefunction be discontinuous?

In a infinite potential well of width $a$, an electron starts in the left half and at $t=0$; it is equally likely to be found at any point in that region. To find the wavefunction at later times, we ...
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Wedge constrained motion, NLM [closed]

A block A and wedge B connected through a string as shown. The wedge B is moving away from the wall with acceleration 2 m/s2 horizontally and acceleration of block A is vertically upwards. Then, (A) ...
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1answer
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Ball hitting a moving wall [closed]

I am pretty new so sorry in advance for any technical issues. I was solving a problem from my book and I don't know how to solve it. If there is a ball moving at some velocity (let's say $v$) and it ...
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2answers
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On solving an RC circuit

Given the following RC circuit: it's required to calculate how the electric current varies and how the other electrical quantities vary. Based on that request, I was wondering if it was correct to ...
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Generalised ideal gas in d dimensions

I'm working through Mehran Kardar's book and I can't get the question on calculating the particle flux of an ideal gas in d dimensions, and help would be great. Show that the number of particles ...
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2answers
190 views

Integration path with opposite direction from the unit vector

The task is to calculate the voltage between points $M$ and $N$ if the electric field vector is known to be $\vec{E}=\frac{V_0\cdot x^2}{a^3} \cdot \vec{i} + \frac{V_0 \cdot y}{a^2} \cdot \vec{j}$, ...
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1answer
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Doubt in the length contraction of rod having velocity at some angle to its axis

I am reading AP French's Special Relativity, and I found an interesting problem there. A rod of proper length L points along the $x$ axis but moves in a direction making an angle of $45^°$ to this ...
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1answer
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The capacitance of two adjacent hemispheres [closed]

like the picture, two adjacent hemispheres(radius $R$, distance $d$, assume the charge is $±Q$ of each side(assume evenly distributed), can we calculate its capacitance? Then what models could we use?
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How does the pressure at point A in the tube change when the tube is accelerated horizontally?

My teacher asked me to solve this question : Suppose we have a tube with a vertical part and a horizontal part. The vertical part (open to atmosphere) of the tube is filled completely and the right ...
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Regarding thin film interference [closed]

I have been stuck on the following question for a while now: I have attached the provided solution side-by-side with the question. The correct options (given) are (B),(D). According to me, only ...
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1answer
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How can I calculate $z_1$ when the ball is on $y_1$?

I'm developing a clone of Pong game and I don't know how to compute this: There is a ball moving on axes $Y$ and $Z$. There is also a paddle on $y_1$ which can only move along axis $Z$. I don't know ...
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1answer
37 views

Electric field of a grounded cylinder capacitor

I was given this question and am confused about the dynamics of the system. Consider this problem: a perfectly conductive tube with a radius $a$ and height $h$ is put into a conducting fluid with ...
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1answer
44 views

How to formalize “does not move appreciably” in a mechanics problem?

I'm working on an exercise from Keith Symon's "Mechanics", ch.2 no.4 (self-study, not homework). The problem is about analyzing the motion of an electron, initially at rest, when a proton ...
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Doubt Regarding Vectorial summation of electric field

So the question was like this : How many neutral points are possible for a system in which N charges are placed at the N vertices of a regular N sided polygon? what I am thinking is that we may get ...
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1answer
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Using voltmeters in RLC circuit [closed]

Consider the following circuit and that we know R, L , C, $\triangle V$ and $\omega$ How can we know the reading in the voltmeters? I'm stucked in this for a while now and could use any help. I didn'...
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Bernoulli effect in gases [closed]

The vehicle moves 160 km/h. Outside is 35 degrees Celsius. Assuming that the air is the perfect gas, what will the temperature feel outside when you put your hand out?
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1answer
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Is there an easy way to treat the anisotropic harmonic oscilator?

In Quantum Mechanics we can deal with the one-dimensional harmonic oscilator by using the trick of the ladder operators. In that case, the original Hamiltonian is $$H = \dfrac{1}{2m}P^2+\dfrac{m\...
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1answer
24 views

Work along a Circle Arc Path

Consider a mass with weight W and force F acting on the horizontal direction going through an arc of a frictionless circular path of radius r and angle $\theta$. Does that mean that the work done by ...
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0answers
44 views

How can the reversal of the sign on a spatial interval between two events not be paradoxical when switching between observers in Special Relativity?

This question is based on two homework excercises I was recently assigned in my Modern Physics course. One of the excercises is to prove that the sign of the time interval between two events can never ...
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2answers
310 views

How to calculate angular momentum of rigid body about an axis?

okay as I read somewhere "angular momentum is not defined about an axis instead it is defined about a point but while dealing with fixed axis rotation or rotation about axis in translation we need ...
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2answers
35 views

Time required for the formation of ice of some thickness in a lake

The air above a large lake is at –2°C, while the water of the lake is at 0°C. Assuming that only thermal conduction is important and using relevant data selected from the given below find how many ...
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2answers
67 views

Quantum Mechanics, eigenvalues with degeneracy

Suppose we have an $n$-fold degenerate eigenvalue $a$ corresponding to an Hermitian operator $A$. Let us consider all different possible linear combinations of n linearly independent eigenfunctions $...
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1answer
159 views

How to determine which number is $r_1$ or $r_2$ in the given equation?

A physicist is designing a contact lens. The material has an index of refraction of 1.40. It also had: an inner radius of curvature (surface that touches the eye) = +2.60 cm an outer radius of ...
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1answer
39 views

Electrostatic Potential, Potential Energy, Method of Images

I am a beginner in problem solving in the field of electrostatics. Well equipped with basic strategies and use of gauss' law. I wanted to analyze the situation below and couldn't wrap my head around (...
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Calculate minimum work and heat absorbed [closed]

Calculate the minimum work necessary to compress 2 moles of an ideal gas from 10 to 5 Liter at 27°C. How much heat is absorbed in the compression process?
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Help with a solid sphere sliding and then rolling

Initially at time $t=0$, a solid sphere slides with velocity $v$ along a horizontal surface. The coefficient of friction is u. Find the required time for the sphere to stop sliding (the sphere will ...
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1answer
43 views

Doubt in a problem of special theory of relativity [closed]

I am studying A.P. French's Special Relativity and there a problem is given As the text points out, an observer does not have a complete view of what is happening everywhere in his reference frame at ...
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One-dimensional atomic chain with m-th Nearest-Neighbor Interactions

I have following exercise: Consider a one-dimensional chain of identical atoms of mass $M$. The springs are not only between nearest neighbors but between all pairs of atoms. Thus, the elastic energy ...
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1answer
32 views

Finding the Normal and Tension on a body on an inclined plane [closed]

Imagine an inclined plane with a body with mass $m$ on it. The body is connected to a rigid wall via string (Assume no slack and the string is parallel to slope). I want to find the normal reaction on ...
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1answer
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Velocity of a swimmer relative to the Earth [closed]

Julia can swim 0.34 m/s in still water. She swims directly east across a river that is 180 m wide and lands at a point that is 81 m north downstream. Determine Julia's velocity while swimming relative ...

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