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1answer
68 views

Tensors in special relativity [duplicate]

I'm trying to understand tensors, but I've come across the following question: Let $T^{\mu\nu}$ by a $(2,0)$ tensor. Give the definitions of $T_\mu^{\,\nu}$, $T_{\mu\nu}$, and ...
6
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4answers
93 views

Bulk flow of air in a long tube between Antarctica and Australia?

I have a 5km diameter clear plastic tube which is open at each end and runs from the center of Antarctica to Lake Eyre in Australia. The tube is on the ground where it can be and at sea level on the ...
1
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1answer
85 views

Hydrogen ionization energy [closed]

Proton and electron have a distance equal to the Bohr radius apart in the hydrogen atom. Knowing this, what's the ionization energy of the atom? So we know $U = -kq^2/a_B$, but this is potential ...
0
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1answer
29 views

Kinematics - moving body [duplicate]

If I have an inclined plane, which has acceleration $\alpha$, will a block placed on the inclined plane slip back with the same acceleration? (considering that the surface is frictionless)
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2answers
36 views

Can clouds quench thirst? [closed]

Suppose you are standing on a mountain surrounded by clouds. You open your mouth and try to swallow the clouds (it's crazy, but still). Can the droplets of water in the form of vapor actually be ...
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0answers
36 views

Finite Square Well Inside an Infinite Square Well

Ok here's a potential I invented and am trying to solve: $$ V(x) = \begin{cases} -V_0&0<x<b \\ 0&b<x<a \\ \infty&x>a \\ \end{cases}$$ and $V(-x) = V(x)$ (Even ...
0
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1answer
49 views

Finding the minimum radius of the pivoted disc

Here is a question based on Simple Harmonic Motion that I tackled just now. However I think I am having an approach to tackle this but I am not sure about it. Ouestion: A uniform disc of radius ...
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2answers
58 views

who will win a race between man, horse and car of same power

Other day I got into a chat with my friend on work power and energy where he asked an intelligence related question the question was like this if a race was conducted between a man a horse and a ...
1
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0answers
31 views

Dipole charge attractions while one of them is turning around other [closed]

There is a electric dipole which is fixed. So angular momentum isn't conserved. And there is charge $Q$ which has initial velocity $u$. My question is: What is the tangential velocity of the charge ...
4
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0answers
77 views

Chandrasekhar Limit [closed]

A white dwarf is essentially a degenerate electron gas, in which pressure of degenerate electrons supports gravitational pressure. As a simplified model of such an object, consider a spherical star of ...
2
votes
1answer
44 views

Power required to keep a freezer at constant temperature

Alright, I'm completely stuck on this and so is everyone else I've asked. A freezer has a temperature Tc = -23℃. The air in the kitchen has a temperature Th = 27℃. The freezer in not perfectly ...
0
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1answer
31 views

An optical system with image from a convex lens forming behind a concave lens

I am having a problem drawing optical ray lines for optical systems. Namely, one which have a formation of image of the first lens beyond the second lens. Take the picture below as an example: In ...
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2answers
29 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 ...
1
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0answers
32 views

Why a transistor is activated when I touch its base with my finger? [closed]

Is my body charged eletrically? If so, how much? Will it work with all types of transistors?
0
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1answer
75 views

How to discover the $F = m\cdot a$ equation from scratch? [duplicate]

Is there a paper or a book that conceptually 'discover' the Newton's famous formula? I've been thinking about this equation, and I really don't know it for sure. Did Newton empirically noticed that ...
1
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1answer
44 views

Parity of a system composed of 2 particles

I have read that for a system of 2 particles, the total parity is given by: $P=P_1 P_2 (-1)^L$ where $ P_1, P_2$= insisec parity of particle 1, 2 $L$ = relative angular moment what's the meaning ...
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1answer
26 views

Work done in pulling a rope from a boat

A boy sitting on a boat pulls on a rope with a constant force $F$ over a duration of time $t$. The other end of the rope is either tied to a bridge or to another freely floating boat of equal mass. ...
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0answers
95 views

A question on an exercise from Gravitation by Misner, Thorne and Wheeler

My question is on problem 4.1 of Gravitation. In a generic case of electric field and magnetic field(i.e not $E=0$ or $B=0$ or $E$ and $B$ perpendicular), define the direction $\hat{n}$ unit vector , ...
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1answer
70 views

Infinite Resistive lattice problem

Ok so while there have been many discussions regarding the solution(say using the Fourier transform or the lattice Green's function approach) to the two-point resistance of an infinite-square ...
0
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0answers
55 views

Finding the total space that an oscillating body has gone through via complex analysis

I was solving my homework and I got to an exercise that stated: An harmonic oscillating body has an equation of $$y(t) = A \sin(t)$$ Find the total space that the body has travelled during $t \in ...
0
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2answers
59 views

combination of cells

There are m*n identical cells of emf E and internal resistance r connected in parallel rows. This combination of cells is connected across an external resistance R. For what arrangement of the ...
1
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1answer
43 views

Effects of firing shells on the Earth's angular momentum

During a certain war, millions of shells were fired by country A towards the west, and even more shells were fired back by country B towards the east. The average momentum of each bullet were the same ...
3
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1answer
737 views

Simple thermodynamics basics - can internal energy be calculated?

Well this got me stumbled, because I've been wondering what the "question" is. One of the example examns got the following question (strangely there are no supplied solution books): A $0.2 {\rm ...
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2answers
69 views

Idempotent Operators

If $P$ is an idempotent operator, $P^2 = P$ and we have a vector $|\psi\rangle$, $P\neq1$, and the relation $$PL |\psi\rangle = L|\psi\rangle,$$ what conclusions can we draw about $L$, which is a ...
4
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2answers
138 views

Electric field in a sphere with a cylindrical hole drilled through it

Suppose that you have a sphere of radius $R$ and uniform charge density $\rho$; a cylindrical hole with radius $a$ ($a\ll R$) is drilled through the center of the sphere, leaving it like a "necklace ...
1
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1answer
81 views

Force between two current carrying parallel wires, multiple proof? [closed]

Having two current carrying (currents $I'$ and $I$) wires of length $a$ parallel to the $z$-axis, one with end points $(0,0,0)$ and $(0,0,a)$ and one from $(a,0,0)$ to $(a,0,a)$, I'm looking for the ...
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2answers
187 views

Determining the neutral axis of an I-shaped cross section with dissimilar materials

Determine the neutral axis of the I- shaped cross section with dissimilar materials. The top rectangle of the cross section is made out of aluminum and the second and third part are titanium ( these ...
4
votes
1answer
75 views

Pressure and Density Using a General Lagrangian

Given a lagrangian of a form: \begin{equation}\mathcal{L}=f(\phi,\partial_{\mu}\phi\partial^{\mu}\phi)\end{equation} where $f$ is a function, I need to derive pressure and density in a FLRW universe ...
0
votes
1answer
44 views

Need help with this derivation (Sound intensity)

I will copy a little bit of what my textbook says. By the way, we're talking about sound here. $$Intensity = (0.5)BwkA^2$$ The textbook claims that by using the relationships $w=vk$ and ...
0
votes
1answer
57 views

Is there any significance to the negative sign on this speed?

A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #$1$). At a time of $60$ s later the friend catches a bus (event #$2$) If the ...
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2answers
366 views

Vibration of pulley and string system

So here's the statement: A pulley of a mass $M$ is hanged using a spring (stiffness of the string being $k_1$), as shown in the image. What is the frequency of the pulley's oscillation? So that's ...
1
vote
1answer
114 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), ...
0
votes
3answers
1k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
0
votes
1answer
150 views

Block Sliding Down a Plane (Perpendicular Velocity)

I'm having trouble understand the concepts for this problem. Here's the problem: A block is placed on a plane inclined at angle $\theta$. The coefficient of friction between the block and the ...
1
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2answers
275 views

Momentum change in colisions (Drude Model)

A particle suffers elastic colisions with scattering centers with a probability of colision per unit time $\lambda$. After a colision the particle is in a direction caracterized by a solid angle ...
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2answers
38 views

How to know the Direction of the Acceleration Vector?

If the exercise doesn't give you the direction, how to know the correct one? Sometimes I assume its to the right and it was actually to the left, and I get everything wrong. Example here: How can I ...
2
votes
2answers
285 views

Pendulum Hits a Mass and Spring

I think this problem’s solution is on the web but after a few days of searching, I can not find it. Can anyone give me a reference? Thanks in advance. A mass and spring are resting on a frictionless ...
0
votes
1answer
37 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 ...
0
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2answers
159 views

Relative motion. Setting course of closest approach (Requested resource recommendation as well)

Let $r_{P/Q}$ be the position vector of $\overrightarrow P$ relative to vector $\overrightarrow Q$ and $v_{P/Q}$ the velocity vector of $\overrightarrow P$ relative to $\overrightarrow Q$. Suppose ...
1
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1answer
50 views

Atom state vectors kets

An atom with two energy levels has 2 states (excited and ground), represented by kets $|e\rangle$ and $|g\rangle$ respectively. The atom has energy $\frac{1}{2}E_\theta$ when excited and ...
5
votes
1answer
122 views

Force problem related to adhesive and bonding

I have two PCBs (printed circuit board), and they are glued by adhesives, as show in the pictures. And the location of the adhesives are indicated on the picture (please notice that NO adhesive is ...
1
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2answers
50 views

Weird Kinematics Homework [closed]

Here's another "hard" homework question I was given on how printers work. (I find it more confusing than it is hard.) I'm supposed to find the horizontal velocity of a charged droplet as it leaves ...
1
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2answers
275 views

Power transfer in a transformer

Can it be proved using the concept of induced emf that power supplied at the primary coil equals power consumed at the secondary. I tried following. Let primary coil be called 1 and secondary be ...
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0answers
32 views

Question about Atwood Machine and Changing Masses

Say we have an object of X Newtons on the ground called object 1, and it is connected to another object called object 2. If we change the mass of object 2 in intervals until object 1 < object 2, ...
0
votes
1answer
53 views

Determining fluid flow velocity from experimental volumetric flow rate data

I would be very grateful if someone helps me with my issue. I have a pump pumping water into a tube. My goal is to find velocity of the fluid flow in another tube that will be connected to the first ...
1
vote
2answers
59 views

Electric Potential of a sphere given electric field

I'm studying for a course in electromagnetism, and I've been given an electric field for which I need to find the associated scalar potential. The field is the field generated by a sphere of radius ...
1
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0answers
26 views

Forces and acceleration due to an angle that varies over time [closed]

I'm having difficulty figuring out how to set a problem up. The problem is as follows: A $5\ kg$ block is being pulled along a frictionless floor by a cord that applies a force of constant magnitude ...
0
votes
1answer
638 views

Magnetic field inside and outside cylinder with varying current density

I am reading through Introduction to Electrodynamics by David J. Griffiths and came across the following problem: A steady current $I$ flows down a long cylindrical wire of radius $a$. Find the ...
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0answers
21 views

A question about superposition and zeroing condition [migrated]

Hey I couldn't do this question for my school and I'd be grateful if you help me. The question is: Calculate the voltage $U_x$ circuit below. Specify zeroing condition of the $U_x$ indicated in the ...
0
votes
1answer
22 views

How to account for the huge difference in susceptibility of liquid and gaseous oxygen?

I noticed this while studying magnetic fields in matter from Griffiths' Electrodynamics book. A table is provided in the chapter which shows the materials with their respective susceptibilities. Under ...