Energy Definition and 999 Threads

I believe I got the first part of this questions solved. For part b, we are asked to find the change in internal energy. We know ΔE=Q+W. The cylinder,gas and piston head are the system. The cylinder and piston head are well insulated, so there will be no head transfer, therefore Q=0. So now...

While reading about electromagnetism from the OpenStax books with my son (and doing some experiments), he asked this question. Suppose I hang a pendulum and make it oscillate inside a coil connected to a Galvanometer as shown in the schematic diagram: Hopefully the image is clear enough. His...

> In the movie "Star Wars: A new Hope", Luke Skywalker blows up the 'death star'. Assume that the 'death star' is a perfectly spherical spaceship with uniform mass distribution. The mass of 'Death Star' ##M=1021 \mathrm{kg}## and the radius ##R=667\mathrm{km}## Estimate the amount of the energy...

a) Two particles have energies E1 and E2, and momenta p1 and p2. Write down an expression for the invariant mass of this two-particle system. Leave your answer in terms of E1 and E2, and p1 and p2. b) A typical photon (γ) in the Cosmic Microwave Background (CMB) has an energy of kBTCMB, where...

Hello, I’ll start by saying I have the answers and the steps to the solutions, but there’s a comprehension disconnect somewhere that I’m trying to figure out. There are two parts to my question but the second one may not apply depending on the answer to the first. I wasn’t sure from the forum...

This problem is in a chapter on momentum in the book basic engineering mechanics explained. Help me Mario

Lets consider T(\vec{p})=\frac{\vec{p}^2}{2m}=\frac{\vec{p}\cdot \vec{p}}{2m}. Then \frac{dT}{dt}=\vec{v}\cdot \vec{F}. And if we consider T=\frac{p^2}{2m} than \frac{dT}{dt}=\frac{1}{2m}2p\frac{dp}{dt} Could I see from that somehow that this is \vec{v}\cdot \vec{F}?

I have doubts about the wording of the exercise: (1) energy density is ##u=\varepsilon_0 (cB)^2## but since the question asks for mean energy density should I perhaps average over ##cos^2 (\omega t)## (there due to the ##B^2##) and thus use ##<u>=\frac{1}{2}\varepsilon_0 (cB)^2##? (2) it seems...

When it comes to explaining some phenomena, I think in terms of mechanisms whereas physics explains through mathematics. With this in mind, I'm trying to compare and contrast the differences between the candidate explanations for dark energy, as nicely summarised on the NASA website...

As I understand, the main theoretical virtue of Guth's inflation hypothesis is that it explains a bunch of otherwise hard-to-account-for phenomena under the standard big bang model without inflation: the Horizon Problem, the Flatness problem, the Monopole problem, and also the problem of how...

With the latest view that free space has virtual particles constantly popping in and out of existence, is it now rational to argue that light can electromagnetically travel through free space for ever and ever without the slightest energy loss? Edwin Hubble found that the general red shift of...

Hi all, I'm not a physics student (although I have a PhD in a different field) and so don't have the math, but I'm trying to interpret a key passage from Krauss' book 'A Universe from Nothing' where he is (trying?) to explain, in 'layman's terms', what Alan Guth termed 'the ultimate free lunch'...

Question

Iron (Fe-56) is in terms of nuclear energy spent, which seems equivalent to saying its nuclides are the most tightly-bound. Does this also make Fe-56 the most stable nucleus, and is nuclear potential energy to stability a general correlation? Do more-stable nuclei generally have less nuclear...

The classical definition to the Kinetic Energy equation is KE=integral of F*dx where F=d(m*v)/dt. When mass is constant, KE=(1/2)m*v^2. I am working on a vibration problem at work and having to review my Lagrangian Dynamics books from 30 years ago. So my question is about all of the authors...

I have used the work energy theorem like all source have shown me an have arrived at the right answer where work one by all the forces is the change in kinetic energy -1/2kx^2 - umgcosΘx +mgsinΘx = 0 is the equation which becomes -1/2kx -umgcosΘ+ mgsinΘ = 0 where k= spring constant u=...

I tried to find states in direct method using ##\frac{E}{E_0}=\:nx^2+ny^2+nz^2## and ##100\:<nx^2+ny^2+nz^2\:<\:136## But it was too long, found it using phi approximation there are around 300 energy states, and Python find around 271 states using direct method but I need manual or recursive...

When the pendulum is released, the Kinetic Energy should be 0. When the pendulum is at the bottom/hits the rod, it should have 0 potential energy. However, I don't quite understand what happens after it hits the rod.

Is energy really not conserved in a constantly expanding universe?

During equal thickness interference, adjust the inclination of the two plates to expand the spacing of interference fringes to 10mm. Then, if a light with a width of 5mm is used for equal thickness interference, whether an interference pattern will be observed, and the width of the interference...

In the initial position the spring is previously compressed, then the block adds a force, and the spring is again deformed. I think the energy balance is incorrect; the potential energy of the spring is repeated.

Hi all, I am currently trying to prove formula 21 from the attached paper. My work is as follows: If anyone can point out where I went wrong I would greatly appreciate it! Thanks.

Been 20 years since college physics. I have a problem where there are basically two inertia wheels on separate shafts coupled by a clutch. One wheel is spinning and the other is at rest. The clutch engages and connects the shafts. What's the final rpm of both wheels? I'm struggling to find a...

Hello! I had a random question while playing around with a garbage can that I hoped y'all could help me walk through: Let's say that I have a hinge on a table, rotating with gravity acting perpendicular to it. Energy is provided into the hinge, let's say by a spring, like so: I want to know the...

My attempt: Let ##M_e## be the mass of the Earth and ##M_m## be the mass of the person. Let ##D_{EM}## be the distance from Earth to Mars and let ##R_e## be the radius of the earth. Defining these constants (leaving off units for brevity): Masses in Kilograms (G is not a mass but I'll leave...

u = (9*10^9)(1.61*10^-19)^2 * (1/[3*10^-15 ]- 1/[2*10^-10]) u = 7.68*10^-14 J but here the question. I have been taught that W= -U so shouldn't the answer be negative?? When i look up at the solution all other sources say that the W = U and therefore the answer is in postive.

Burning waste in a waste-to-energy plat, can more energy be produced by burning the trash then the amount of energy needed to heat the trash to the point it vaporises? (to turn it to ash) eg we have 100 J of energy inside some rubbish, and this energy would all be released when we incinerate the...

Hello! If I have a single ion traveling at a given energy (on the order of 10 keV), is there a way to read out its energy in real time with a single pass? Basically I was wondering if there is a device able to measure the current or magnetic field induced by the ion passing through it (while...

I have two questions: 1) Is it possible to cut the material with a laser cutter or scissors or do I need to have a specific tool? 2) What is the best way to attach the PZT-5H material to the beam but it can be easily detached for using it on another beam ( so no epoxy glue)?Thank you

I was enjoying my (very short) hot shower this morning and realized that the lovely warm water was flowing over my body (sorry - too much information) only once and then disappearing down the drain. This water - and what comes out of the washing machine, dishwasher etc. could be at a seriously...

Physical objects have well defined shapes, but does energy ever create well defined shapes or can it only take shape within matter?

Energy and mass are interdependent and electrons can manifest as particles and fields as do all other particles, but is it generally true that physical(classical) matter is a peculiar type of energy that can(for some reason? What?) manifest as physical objects?

Hello, in one of tasks of my liquid scintillation lab is to determine the average energy. You can see from the graph that data I obtained is similar to this one that I have a excel sheet data. X-axis is for beta particle energy from 0-156keV while y-axis counts of the particles. So according to...

Why the wheel moves? I intuitively think that it should move to right but I don't really understand why. When AB gets longer by x each end gets longer by x/2 so W goes to right and down. This will create torque and body will move. This explanation seems valid but I can't calculate anything and...

I am totally confused about the task. Any help will be nice. Thank you so much

My book says that emission spectra are produced when an electron in excited state jump from excited to lower energy states. It also states that solids and liquids produce continuous spectra and it depends upon temperature only (is this black body radiation?). I know, Electrons around a nucleus...

The slinky is designed to fully contract in 1 second. During this one second, the mass is weightless and move up at constant speed of 1m/s. After 1 second the mass gain 1m height in potential energy. Am I missing something?

Hello everyone. I have just complete an experiment calculating the speed of a muon. I got it to 2.6E8 m/s, however I know that they are created at close to speed of light to be able to get down to Earth's surface in their short lifespan. This speed could not have been its initial speed, as it...

for the first question, i thougth that 0,5 A is the answer? for the second question: i used the E =hc/λ to found the E. but i got a little confused which equations to find ∆E, since there's no ∆t. or should i search the momentum, then use the λ= h/p ?

It is known that constructive interference in one place must be compensated for by destructive interference in another. Take a simple Fabry Perot resonator for example. The interference occurring at both sides of the first mirror (assuming one incident electric field) compensate each other out...

I got curious about firearm ballistics and googled something similar to "bullet momentum vs kinetic energy". IIRC, momentum P = mv (checked); and kE = (mv^2)/2 (also checked). So I essentially wondered if it's worse to get hit by a bullet with greater kE than by one with lesser kE, presuming...

Mentors note: split from https://www.physicsforums.com/threads/energy-mass-equivalence.1003564/ How do you measure energy?

I have been analysing the power that a cyclist puts out during a standing start and the numbers don't seem to match the effort that is going in! Here's a real example: Cyclist (93kg incl bike) moves 15m from standing start in 4secs (average velocity 3.75m/s). Assuming a constant acceleration, of...

When we connect tungsten filament light bulb to the battery, filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor. Heat is eventually converted to electromagnetic radiation making light bulb shine. Light energy comes from flow of electrons and...

Hi, I'm a current senior in college, and am applying to grad. schools for fall 2022. I'm interested in high energy theory, and I have had some research experience in ads/cft correspondence, kaluza-klein theory, computational particle physics. However, I'm not certain as to which particular topic...

First I picked an arbitrary state ##|ϕ⟩=C_1|φ_1⟩+C_2|φ_2⟩+C_3|φ_3⟩## and went to use equation 1. Realizing my answer was a mess of constants and not getting me closer to a ground state energy, I abandoned that approach and went with equation two. I proceeded to calculate the following matrix...

[Mentors' note: This thread was split off from https://www.physicsforums.com/threads/system-potential-energy-and-nonconservative-forces.1009237/] This is not a particularly helpful way to think about things; For a general mechanical system, you usually split the specified forces into external...

I tried using the equations above, but I wasn't really able to come up with an intuitive explanation. From my understanding, the electric field vector only varies in the x-y plane while the magnetic field vector only varies in the z-y plane. Also, both vary sinusoidally and both reach extrema...

Hello, I am trying to get my head around the idea of nonconservative forces doing work and changing the potential energy of a system. First of all, forces acting on a system can be: a) internal and conservative b) internal and nonconservative (friction, pushes, pulls, thrust, etc.) c) external...