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
15 views

A question about a small block sliding down a larger one, involving conservation of momentum and energy

I have been working on a problem for some time but haven't found a solution yet. I am mainly looking for a hint that will help me find a breakthrough and not a full solution. Here is the statement of ...
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17 views

Trace distance expressed with maximization of probabilities

I'm studying chapter 9 of Nielsen and Chuang, where trace distance is defined by equation (9.1) $D(p_x,q_x)=\dfrac{1}{2}\sum_{x}|p_x-q_x|$ and later on the next page (also asked to be proven in ...
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8 views

Conformal mappings in electrostatics applied to an infinite conducting fence in a uniform electric field

A long straight fence made of conducting wire mesh separates two fields and stands one metre high. Sometimes, on fine days, there is a vertical electric field over flat open countryside. Well away ...
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36 views

How can you get distance traveled from time when acceleration is a function of distance?

Let's say object $A$ has an initial velocity of 0 m/s and is $x_i$ meters away from object $B$. Object $A$ is accelerating towards object $B$ at $a=x^{-2}$ where x is the distance between the two ...
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0answers
17 views

Heisenberg uncertainty principle and minimum Energy of a system

A body has the total energy $E=p^2/2m+mgx$ if $x>0$ and it has the total energy $E=p^2/2m+1/2*kx^2$ if $x<0$ .Find the minimum Energy of the system? This is my two different attempts of solving ...
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0answers
21 views

I'm looking for the solution for this question regarding Schrödinger equation [on hold]

I'm studing for my quantum mechanics exam and I'd appreciate any help regarding this question
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2answers
43 views

Coefficient of friction in pulley system

EDIT: Picture doesn't show the mass of $\mathrm A$. It is $60\ \mathrm{kg}$. My attempt: I placed my coordinate system with $x$-axis parallel to the ramp surface and $y$-axis parallel to the normal ...
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0answers
39 views

Physics help please [on hold]

Calculate the distance an arrow will land from a hunter if he releases the arrow with a speed of 20m/s at a 60 degree angle above the horizontal. The tip of the arrow is 1.5 m above the ...
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0answers
20 views

Find equivalent resistance [on hold]

The equivalent resistance between A and B is
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0answers
17 views

Find electron-hole recombination rate?

In an n-type semiconductor, the thermal equilibrium electron concentration (n0=1015/cm3) and the intrinsic carrier concentration (ni=1010/cm3). The mean life time of minority carriers is 1us. The ...
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15 views

Electric field of a charge distribution on an arbitrary curve

I want to calculate the electric field intensity at a point $P(x,y,0)$ for charge distribution lying on an arbitrary curve such as in the figure. We know the coordinates of some points on curve. What ...
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26 views

How to calculate the wavelength with just the frequency? [on hold]

there is a training question in my study and I've completely lost how to work this out. Can you give me any tips or which steps I have to go to calculate this? Using the relationship between ...
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4answers
87 views

Why is Lorentz force linear in velocity?

I am working on the derivation of the Lorentz force. (I know that Lorentz force is in some sense definition of fields, but still, there is nontrivial dependence on velocity) I want to derive that ...
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3answers
130 views

Special Relativity - Simultaneity of events

For the discussion below, consider only 1-space dimension, $x$ Let $E_1$ and $E_2$ be two physical "events". Let $S$ ans $S'$ be two IRFs. Let the coordinate of $E_1$ be $(x_1,t_1)$ w.r.t to $S$ and ...
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0answers
25 views

Longitudinal stress [on hold]

A uniform wire is subjected to longitudinal tensile stress of $5 \times 10^7 Nm^{-2}$. If the overall volume change in the wire is $0.02\%$, then the fractional decrease in the radius of the wire is?
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0answers
32 views

To show that any central force field is conservative

Denote the radial and cross-radial components of a conservative force field by: $F_r$ and $F_\theta$ respectively. [The the central orbit is planar, i.e. a plane curve]. We need to show that $\nabla \...
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0answers
34 views

What is the meaning of $\tau$=$Gb/l$

What is the physical meaning or intuition of the Shear Stress vs Shear Modulus and Burger Vector over length relation($\tau$=$Gb/l$). I have seen this formula being used to determine length in case ...
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1answer
19 views

Measuring small changes in length using the micrometer screw gauge

Which of the following method/instrument cannot be used to measure small changes of the order of a millimeter occurring in a length of about 50cm. 1)spherometer 2)travelling microscope 3)meter ...
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1answer
30 views

Electrostatics and Conservation of angular momentum [on hold]

A charge $+Q$ is fixed. Another charge $+2q$ and mass $M$ is projected with a velocity $V$ with an angle of 30 degees from a distance $R$ from the fixed charge. Minimum separation between the two ...
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1answer
53 views

Free fall time after being accelerated

An elevator car whose floor-to-ceiling distance is equal to $2.7m$ starts ascending with constant acceleration $1.2 m/s^2$; $2.0 s$ after the start a bolt begins falling from the ceiling of the car. ...
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0answers
33 views

A charge accelerating while confined to an equipotential surface

Suppose I had the following in Cartesian $(x,y,z)$ space, where $x$ is horizontal, $y$ is vertical, and $z$ is depth: A negligibly thin conductive rod extending from $(0,1,0)$ to $(0,+\infty,0)$. An ...
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0answers
22 views

Young's Experiement [on hold]

My question is about 2 slits where there is an monochromatic source of light and: 100 lambda - distance between slits, wide of slits is 20lambda and 40lambda L is the distance to the screen. ...
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0answers
35 views

Is my method correct? [on hold]

Suppose we have two point charges, one negative and one positive separated by a distance d and we want to find the potential of the dipole a point $P$ where the distance of the positive charge to $P$ ...
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1answer
33 views

What is the relation between Earth's orbit and orbit of another planet around Sun? [on hold]

Lately, I come across the following problem, "The maximum and minimum speeds of a comet that orbits the Sun are 80 and 10 km/s respectively. The ratio of the aphelion distance of the comet to the ...
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1answer
30 views

Scale factor for flat universe filled with radiation and cosmological constant

I am trying to solve problem 1.20 in the book 'Physical Foundations of Cosmology' from Mukhanov. In the problem, we should show that the scale factor $a$ for a flat universe filled with cosmological ...
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1answer
38 views

How can we see the microstructure of steel samples at room temperature?

When we intend to see the microstructure of a steel sample at a temperature say 950 $^\circ$C they say we quench it in order to freeze the microstructure. However, if we quench it are we not going to ...
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0answers
24 views

The physics behind amusement park ride [on hold]

i want to know about the physics behind tora-tora ride. How do tora-tora ride work? The physics theory in tora-tora ride?
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0answers
22 views

Very simple vector question (solid state) [on hold]

Problem Statement Graphene is a 2D crystal made entirely of carbon atoms. The crystal lattice can defined by the lattice vectors a and b, where the magnitudes |a|=|b|= 2.46 Å and the angle between ...
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0answers
18 views

Physics 2 Wave question 3rd harmonic frequency [on hold]

A string vibrates at its third-harmonic frequency. The amplitude at a point 35 cm from one end is half the maximum amplitude. How long is the string? I cannot find the correct answer anywhere online ...
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1answer
29 views

How to express the $Q$-value for alpha decay in terms of binding energy of the relevant species?

I have 2 questions regarding the solution to the following question: The solution states that: Mathematically, I understand how the end result $$Q=BE\left({}^{A-4}_{Z-2}\mathrm{Y}\right)+...
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1answer
25 views

Avarage Speed conventional formula VS Mean Value of Multiple Speeds [on hold]

Here the basic problem: The motion of an extraordinarily jubilant bird flying straight up and down is given by the graph below, which shows the vertical position y as a function of time t. What was ...
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3answers
31 views

Why we add acceleration of celestial body with acceleration of spaceship to determine force exerted by space ship on astronaut?

The acceleration due to gravity acts in the downward direction, and a spaceship accelerates in an upward direction. Therefore, why do we add the accelerations together instead of subtracting them?
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1answer
29 views

If a rectangular loop is present between two wires carrying current in same direction but fluctuating, what will be the direction of current in loop [on hold]

The current in $I_1$ is continuously decreasing and the current in $I_2$ is continuously increasing, then what will be the direction of current in the loop? Here's what I know, the wires carrying ...
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0answers
22 views

Help with this gaussian integral [on hold]

Can someone explain how to do this integration...i know some basics of integrating gaussians..please keep it as simple as possible
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2answers
49 views

Solved problem on radioactive decay

I encountered a question that was given the disintegration rate of a radio active source measured at the interval of four minute. The source is consisted of two types of radio nucleus and the half ...
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0answers
35 views

Anticommutation relation of Grassmann numbers

Let $c,c^*$ be the fermion annihilation/creation operators and $\xi,\xi^*$ denote Grasssmann numbers where $$|\xi\rangle = \exp(-\xi a^*)|0\rangle$$ is the coherent state. Then why is it true that $$ \...
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0answers
14 views

Connect two charged insulators [on hold]

if we have two charged insulators. One positively charged and another negatively. if we connect them together, their charges transfer from one to another or not? transfer charge with conducting occur ...
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0answers
38 views

Finding potential given a force [on hold]

The question is you have a force given by the expression $ \mathbf F=-K(y\hat i+x\hat j)$, find the the work done in moving a particle from origin $(0,0)$ to $(a,0)$ to $(a,a)$. I tried finding the ...
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0answers
18 views

How to solve this electrostatics problem about induction of charge? [on hold]

Consider two parallel, grounded, conducting plates located at x = -L and x = L. A charge of Q = -92 microcoulombs is placed at (L/2, 0, 0). What is the total charge induced on the plate located at x = ...
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0answers
34 views

Photon vacuum polarization one loop diagram with W bosons [on hold]

I have to compute the one-loop integral for the photon vacuum polarization with a W boson loop in the unitary gauge SM with dimensional regularization. After performing the Lorentz algebra I end up ...
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2answers
21 views

Doppler shift moving parallel to wall

Suppose you are screaming and running in an area parallel to a wall. What would be the frequency you hear considering that you are getting away from the part you've passed and getting close the parts ...
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0answers
35 views

Relativistic Aberration Formula Derivation: looking for a hint

The literature on relativistic beaming / doppler beaming is scarce, so I hope the community can shed some "light" on this topic. I want to derive a formula for the phenomenon known as relativistic ...
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1answer
22 views

Interplanar distance calculation with Miller indices [on hold]

what is the perpendicular distance between two planes indicated by Miller indices (2 0 0) and (2 1 0) in a unit cell of a cubic lattice with a lattice constant parameter a
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2answers
51 views

Contracting Riemann Tensor Troubles

It has been several years since I looked at General relativity, and I am trying to brush up on it because it was always interesting and I am in need of it for my research. Specifically, I am looking ...
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0answers
13 views

Finding the torque on a square shape [on hold]

I came across this question when practicing rotational dynamics online. The answer is D, which is what you get when you multiply the forces by the distance to the center: $8\frac{\sqrt{2}}{2}-4\frac{\...
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0answers
41 views

Fourier transform (cos(x))^4 from 0 to 1 [on hold]

I was curious, if I were to Fourier transform $\cos^4(t)$ from $[0,1]$, what would that be? I am doing this because of the Stefan-Boltzmann law $E=\epsilon\sigma T^4$. The temperature that I'm working ...
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0answers
33 views

Degree of freedom of two particles in plane [on hold]

Number of degree of freedom of two particles connected by a rigid rod moving freely in plane is________? please explain
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0answers
71 views

How do I calculate the total resistance of this circuit? [on hold]

How do I calculate the total resistance of this circuit? From the data from a site it can be calculated that the total resistance is $\frac{12\ V}{5.14\ A}$ which is $2.33\space \Omega$. But I don't ...
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0answers
39 views

Finding the temperature of a gas using the $P$-$V$ diagram [on hold]

I need to know a way to relate the P-V curve of an ideal gas to its temperature.I found a similar question on stackexchange but couldn't understand how the relationship between a point and the ...