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Capacitors in Series and Parallel [closed]

I'm working on a physics project and we're disagreeing on how to analyze a circuit. I think the circuit should be $(1/c_1 + 1/c_2)^{-1} + c_3$ and other people in my group think it should be $((c_3 + ...
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1answer
29 views

What is the smallest resistance that can be used in a 5 V circuit if the resistors available are rated for 1/4 W? [closed]

What is the smallest resistance that can be used in a 5 V circuit if the resistors available are rated for 1/4 W? What is kind of throwing me is that it wants the "smallest resistance that can be ...
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2answers
66 views

Difficulty evaluating a complex integral on Griffiths

This actually a question from Griffiths QM. (Q2.21) I have difficulty understanding integrals involving imaginary components. In this example, it looks like the first term (encircled in red) explodes ...
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1answer
63 views

Using Cosine Law to Find Net Electric Force on Charge Always Results in Positive Number?

In order to determine the net force other charges have on a particular charge, you must take into account each individual electric force between the charge and the charge of interest. However some of ...
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2answers
47 views

What is the Planck quantity of an expression?

I don't know what a Planck quantity is (I tried google), but someone at school gave me this problem. As you know, I have no idea how to approach this due to the weird terminology. Find the Planck ...
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1answer
92 views

How did they solve for $y = -(1/2)gt^2$? [closed]

I am reading through my Physics book lesson and these are the known and unknown values they are discussing. ! So can you please tell me how they went from $y = \frac {-1}{2}gt^2$ to $t = \sqrt ...
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0answers
33 views

Compute the colour in the AB photometric system [closed]

I have a question for homework and don't get it at all: Consider two filters as shown in the figure below. Compute the colour S1 - S2 in the AB system for a star with flux: where is a constant ...
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2answers
31 views

If a mass $m$ whirls with constant speed $v$ at the end of a string of length $R$, what is the force on $m$ in the absence of friction or gravity? [closed]

This problem appears in a book I'm reading. The solution is given as follows: The only force on $m$ is the string force $T$ which acts towards the center. The radial acceleration is $a_r = \ddot r ...
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2answers
55 views

Pulling on a weakened rope - where will it tear?

Let's say I have a rope of 10m length and it is weakened in 3 spots: at 2.5m, at 5m and at 7.5m. Weakened means that if enough tension is applied it will tear at these points (all points are equally ...
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1answer
76 views

Special Relativity: Finding the Euler Lagrange of a massive particle

Knowing that $$\tag{1} L= -mc\sqrt{-\eta_{ab}\frac{d\xi^a}{d\lambda}\frac{d\xi^b}{d\lambda}}$$ we get $$\tag{2} p_a=\frac{\partial L}{\partial(d\xi^a/d\lambda)} = m\eta_{ab}u^b.$$ How come? If I ...
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1answer
189 views

Question on hadamard gate and cnot gate circuit tables

I'm trying to solve this problem for homework: Now show that if the CNOT gate is applied in the Hadamard basis - i.e. apply the Hadamard gate to the inputs and outputs of the CNOT gate - then ...
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0answers
42 views

Thermodynamics: Caclulate final temperature with hot metal in gas [closed]

I've been working on this problem for a couple of hours now, and I think that I simply don't understand the basic principles that tie into the problem: (note that I attempted this problem and it was ...
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0answers
40 views

Physics - Waves (Help!) [closed]

When a microphone is moved along the line LS, the trace seen on the c.r.o. varies from a MAXIMUM amplitude to a MINIMUM amplitude and then back to a MAXIMUM amplitude. Sketch this sinusoidal graph ...
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1answer
93 views

H-theorem and Boltzmann equation applied to Boltzmann distribution

Using the Boltzmann equation: $$ \frac{dH}{dt} = \int_0^{\infty} dr \int_0^{\infty} ds W(r,s)[p_r - p_s][\ln{p_r} - \ln{p_s}],$$ and assuming $p_r = e^{-\beta r}$, the equation looks like $$ ...
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1answer
52 views

Simple Harmonic Motion homework [closed]

Suppose we have a rod of mass $m$ and length $l$ which is pivoted at center and two springs of spring constant $k$ are attached at opposite ends so that it performs simple Harmonic motion when ...
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0answers
122 views

The motion of the magnetic bob

I have two simplified mathematical models which should describe the motion of a magnetic bob, but there is a minimal deviation. model A (RED): use of conservative force: $V= V_M + V_G = ...
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2answers
290 views

Would this box on the floor rotate based on friction?

There is a floor that friction is proportional to its velocity (like $F=-kv$) and there is a box with its width as $l$ and its height as $h$. (you may assume that $l$ is longer than $h$). It is on the ...
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0answers
27 views

Statics and 3-D Equilibrium of Rigid Bodies [closed]

and Thank You for viewing this problem! I am new to Stack Exchange, I never heard about it until a friend recently introduced me to it.. The problem: The bent rod ABDE is supported by a ball and ...
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1answer
169 views

Rigid body problem in 2d

I have some questions about this exercise: In an horizontal plane, a $OA$ bar with mass $m$ and length $a$ moves, with another bar $AB$ (same mass, double length) attached in the point A. In the ...
2
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1answer
45 views

Thin-wedge Interference Problems (Classical Waves Problem)

I would like to solve the problem on the following image: My question is: Why is the answer to (a) a minimum? When the light wave hits the top surface of the top glass, a wave will be reflected ...
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3answers
51 views

Potential due to a continuous charge distribution on ring

Derive the formula for the potential at point $P(0,0,z)$ directly above the center of a ring of charge with radius $R$ and uniform charge density $\lambda$. My attempt: Since $$\lambda= ...
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1answer
80 views

Rotating platform with pulleys and stacked blocks

This was a practice test question. Consider the following figure. (If the frictional coefficients are unclear, between A and B we have $k_1 = 0.3$, B and platform is $k_2 = 0.2$. If you further ...
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2answers
71 views

How would an electron bunch/beam look different in the rest and lab frames?

With respect to special relativity, I was wondering how the spatial dimensions would differ between the rest and LAB frame of an electron beam. System: Electron bunch/beam traveling in linear motion. ...
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2answers
57 views

Prove Biot-Savart law, assuming that $\vec{A}=\frac I c\int \frac{d\vec{L}}{r}$

Prove Biot-Savart law, assuming that $$\vec{A}=\frac I c\int \frac{d\vec{L}}{r}$$ $$\vec{B}=\nabla\times \vec{A}$$ Any hint on what to do next?
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1answer
92 views

Shell model of an odd-odd nucleus: $^6$Li

Lithium-6 isotope has an approximate magnetic momentum of $0.88\ \mu_N$ in its fundamental nuclear state. I'm trying to find its angular momentum and parity. I found in a standard table: $I=1^+$ and ...
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3answers
48 views

Finding charge density from from differential form of gauss law

I didnt get why he didvided and multiplied by r^2.This question is from d j griffith .
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1answer
28 views

The luminosity function

I'm trying to figure this out for the case... Supposedly the average luminosity will be equal to but how :S I know is the number density of galaxies per unit volume and luminosity but that ...
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1answer
45 views

Have $2s_{1/2}$ and $2p_{1/2}$ the same energy?

I have always known that p-states are more energetic than s-states. But in this picture I see the following: And it confused me. Could anyone explain if both levels have the same energy?
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1answer
25 views

If a body move around the circle $n$ times then? [closed]

What will be its angular frequency if it rotates $n$ time in one second? I know its a homework type question but I am self studying and cannot have someone solve this problem. Help me please.
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0answers
33 views

Chemical potentials at triple point

How to prove that chemical potential of each phase at triple point are equal? My attempt: At phase transition, $P$ and $T$ are constant and using $dG=0$(Gibbs free energy at minimum) at equilibrium ...
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2answers
37 views

Orientation of a rocket going in a circle?

This problem is from my physics homework: A rocket is moving at constant speed in a perfect circle in deep space, far away from any planets or stars. The diagram below shows the circle the ship ...
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1answer
100 views

Geodesic equation from Euler - Lagrange

There are several ways to derive the geodesic equation. One of which is the variational method which I seemed to understand it because it was written in great details. Then it was mentioned that the ...
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2answers
35 views

Rolling of a disk and sphere

I am confused regarding the fact that when a disk is rolling on an inclined plane without slipping and similarly a solid sphere is rolling on an inclined plane without slipping then the sphere has ...
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1answer
118 views

GR exercise: falling particles on earth's surface

I'm having some trouble with Exercise 5.1 in Shapiro's BH,WD&NS book, which goes as follows: Consider two particles of mass $m$ at distance $r$ and $r+h$, such that $h\ll r$, on the same ...
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1answer
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Calculating specific orbital energy, semi-major axis, and orbital period of an orbiting body

Is it possible to calculate the specific orbital energy $ϵ$, the semi-major axis $a$, and the orbital period $T$ (or $P$) without any of them being available to you? The values I do have available to ...
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2answers
28 views

Finding the point of passing between two objects of different velocities

Let's say an there are two objects or vehicles, both of them travel towards the same direction with constant velocities, the other object being slower than the other. How do you calculate at which ...
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1answer
29 views

What is the ohmic value of a resistor that will dissipate 1 W when the voltage across it is 2 V?

I've been learning about Ohm's and Watt's law throughout this chapter so I'm already familiar with substituting Ohm's Law for part of Watt's law to get values. But nowhere in the chapter did it go ...
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2answers
46 views

Does the gravitational acceleration change value with height?

My prof asked me to do a graphic of a given function and I have to just to vary the gravitational acceleration $g$ and the height $H$. If I know the interval in which $H$ is defined :$[500,2000]m$, ...
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1answer
23 views

Confusion about horizonally projected body

DESCRIBED IN IMAGE CLEARLY In the text book, I got the initial velocity of x-component initial velocity Vxi, Vxi = Vi cos(0); (0 = zero) but what if it is like the picture i showed, first it was ...
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1answer
44 views

Projectile Motion Tricky Problem [closed]

A particle is projected from point A with a velocity u at an angle theta to the horizontal. At a certain Point B, it moves at right angle to its initial direction. what is the time taken from A to ...
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1answer
27 views

Reason behind the train remaining intact to the Train track

I was wondering why trains moving at such hard speeds remain intact to the railway track even while turning. Is it because of friction ?
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1answer
59 views

Current in Magnetic fields

I have two magnetic fields question (high school level) which require clear answers... When a current carrying conductor, such as a copper wire, is placed in a magnetic field it will experience a ...
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1answer
64 views

Two masses on frictionless table with one string connecting both masses on ground and the other string [closed]

From Morin's Introduction to Classical Mechanics page 342: A solid cylinder of mass $m$ and radius $r$ lies flat on frictionless horizontal table, with a massless string running halfway around ...
2
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1answer
53 views

The massive Thirring model

I am trying to find conservation laws in the following coupled equations: \begin{equation} -af(x) + i\frac{\partial f}{\partial x} + g(x) + |g(x)|^2 f(x) = 0 \end{equation} \begin{equation} -ag(x) - ...
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3answers
37 views

Moment of inertia of rods

Ok so I'm extremely comfortable with calculating moment of inertia of continuous bodies but how do we do it for a system not continuous. For example if 3 rods of mass $m$ and length $l$ are joined ...
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1answer
129 views

How to calculate the amout of time for oil to get out from a pneumatic cylinder?

I have a system. You can assume it is just a 1" diameter steel pneumatic cylinder (1 foot long). Assume we ignore the bore size issue at this point. One chamber is filled up by oil (6" of volume), ...
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0answers
57 views

How to show circular orbit as a precessing ellipse

A uniform distribution of dust in the solar system adds to the gravitational attraction of the sun on the planet an additional force linear in $r$ where m is the mass of the planet, k is a constant ...
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1answer
67 views

Momentum Representation vs Position Representation

We are given an operator $g$ from $\mathcal{l}^2(\mathbb{Z})$ to $\mathcal{l}^2(\mathbb{Z})$, i.e., the space of functions that are square summable over $\mathbb{Z}$ such that ...
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2answers
52 views

Uniformity in a solenoid

I know the magnetic field strength increases as the number of turns in the solenoid increases. However, I've learnt the field inside the solenoid is usually nearly uniform. So, does the number of ...
3
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1answer
285 views

Semiconductor problem: how much Boron is required to establish a certain amount of charge carrier density

The problem description is as follows: Boron is used to dope 1 kg of germanium (Ge). How much boron (B) is required to establish a charge carrier density of 3.091 x 10^17 / cm^3. One mole of ...