Conservation Definition and 999 Threads

I understand the 1st law of thermodynamics developed as a generalization based on experimental observations, in that an exception has yet to be found in thousands of situations, so it is considered to hold true in all possible situations. If that is how it developed, is there any other theory or...

We have two cylindrical shells (with radii a and b and charges +Q and -Q) along the z-axis. There is a uniform magnetic field (in the positive z-direction) out to radius r from the z-axis. Because of the symmetry, the total field momentum is zero. Suppose we now connect the shells using a wire...

I was watching a video where the author (Isaac Arthur) says it's possible to use mirrors and lens around a star to focus the energy to boil a planet on the other side of the galaxy. At first it sounds reasonable, surely you have enough energy, but I have doubts that mirrors would be able to do...

Homework Statement Two blocks move along a horizontal frictionless surface and collide head-on with each other. The mass of the first block, moving to the right with speed v is m, and the mass of the second block moving towards the left with speed 3v is 2m. After the collision, the block of...

Why ain't momentum conserved when external force acts on the system? Please explain with an example.

Hello everyone, I'm needing help understanding how to take the conservation of momentum equation and substitute moment of inertia inplace of mass in the equation. I understand this is a linear equation and I'm trying to incorporate angular momentum. I just want to determine the speed of the ball...

Hi PF! Suppose we have a water wave with mean depth ##H## with disturbance ##\zeta## above/below ##H## propagating through a channel of thickness ##b##. The book parenthetically remarks that the continuity equation becomes $$\partial_t(b(H+\zeta))+\partial_x(bHu)=0.$$ However, when I try...

A consequence of Heisenberg's Uncertainty principle is that particles energy level can fluctuate their amount of energy, e, for a short amount of time, t, as long as e x t < h/4pi (where he is = to Planck's constant). So does that not violate the law of conservation of energy?

How do you account for the conservation of momentum for a photon? Specifically, if you have light traveling in a medium where the refractive index is not constant. For example, a graded index multi mode fiber optic. So here is another diagram to help articulate my question. Inside this graded...

Homework Statement This is a common massless string and pulleys problem. I'd just like to understand why, according to the solution, l_2 + 2l_1 = constant. It doesn't seem to me that two times the l_1 length is equivalent to l_2. Can somebody explain? Homework EquationsThe Attempt at a Solution

This is not coursework, it is from a past paper (which we don’t have solutions for) and am doing preparation for this years exam. 1. Homework Statement Particle ##A## with energy ##E_A## hits particle ##B## (at rest), producing particles ##C## and ##D## in the reaction A+B \longrightarrow C...

Homework Statement ρ= density, vi = i-th velocity component, gi=i-th component of gravity vector, p=pressure, μ= viscosity, D/Dt = material derivative Homework Equations Continuity equation: div v = 0 The Attempt at a Solution

Hi everybody, I apologize if something like this has been asked before but I have been unable to find an answer through searching. If a weight is carefully added to a moving cart then the cart should slow down due to conservation of momentum. How is it that the cart has accelerated without a...

Hello! I am having problems with this exercise if someone can please help me. Homework Statement In order to go all the way around a frictionless circular loop of R=2.5 m , how fast must a mass be moving as it exits at the bottom of the loop. 2. The attempt at a solution I am doing this...

In a closed system, I know the rider wouldn't be able to change the combined center of gravity of the system by moving his weight around. If he pushes the bike to lean to the right, he would go to the left by the amount that would keep the combined cog the same. But a bike with tires and a road...

Homework Statement If it can be assumed that the car has the same speed at points A and E, which of the following statements is true? a. The net work done in this system is 0 b. The net work done in this system is positive c. The net work done in this system is negative d. The net work done in...

Homework Statement A 39.00 kg rod of length 2.8 m is hanging vertically by one of its ends that is free to swing in a complete circle about a frictionless axle/pivot. The rod has uniform mass density. Suddenly it is struck horizontally by a 5 kg putty that sticks to the center of...

Source: Çengel/Cimbala. Above part is confusing for me from some points. First of it what can a closed system refer to? I just understand a piston/cylinder arrangement with an ideal gas in it. But this concept must be more comprehensive than I have it in my mind. Second, does "closed system...

Let's say you've got a boat filled with n frogs of mass m each. Let's also say that all the frogs jump simultaneously out of the boat in the same direction with velocity v, then the boat will get a velocity v1 in the opposite direction because of conservation of momentum. Now if we instead let...

Homework Statement The same horizontal force is applied separately to two objects initially at rest on a horizontal, frictionless surface. Object A has less mass than object B. In each case the force is applied for the same length of time. Which of the following statements is true after the...

Homework Statement A block of mass 10kg starts at the top of a frictionless track which forms a quarter circle with radius 10m. It is given an initial downward velocity of 10m/s. What is the velocity at the bottom of the track? Homework Equations KEtranslational, f+ KErotational...

Hello.I have a question about entropy of a thermodynamic system. 1)If we have let say a gas that is separated by some thermo isolated walls (so no heat goes in or out) does the entropy of that gas conserve? I taught that if S=dQ/dt, because Q=0,then the entropy should be conserved. 2)So,does the...

Homework Statement its a nuclear physics problem : a deuterium atom with energy 4Mev collides with a boron atom B5/10 in an elastic collision producing an H1/1 and B5/11 ,the Q of the reaction = 9.23 Mev . find the E,E' , the energy of the boron and the hydrogen the unknowns : E,E', theta of...

Homework Statement [/B] A thin uniform bar 2.00 m long and weighing 90.0 N is hanging from the ceiling by a frictionless pivot. It is suddenly struck 1.50 m below the pivot by a small 3.00 kg ball initially travellimg horizontally at 10.0 m/s. The ball rebounds and moves in oppossite direction...

Homework Statement 2. Homework Equations Conservation Mechanical Energy The Attempt at a Solution I need to find how close to the wall the block will come. Since there's no friction, I presumed there'd be enough energy, and only enough energy, to go the same distance d to the left of A...

Hello! I read some stuff about "attempts" to test some aspects of string theory at LHC and I was wondering if there is any deep reason behind the conservation of energy in general or it is just based on the fact that it holds in all the experiments (excluding uncertainty principle arguments)...

What equation in QM show us that symmetry in quantum-mechanical phase implies charge conservation?

I intuitively understand macroscopic vibration, but trying to understand what it means for a particle to vibrate doesn't seem to make sense from the classical understanding I have of momentum and energy. First, are particles even said to vibrate or have vibrational energy? If so, how is momentum...

I would like to check my understanding for this problem : A puck with mass ##3m## is stationary on a horizontal friction-less surface. It is being impacted in an elastic head-on collision by another puck with the mass ##2m## traveling with speed ##u## to the right. Find the speed and direction...

In general relativity, does momentum conservation mean conservation of 4-momentum or 3-momentum

Homework Statement A tennis ball and basketball are dropped from a height of 1m (the tennis ball on top of the basketball). The tennis ball has a mass of 75g and the basketball has a mass of 1kg. When dropped separately, the tennis ball bounces to a height of 0.5m and the basketball to a...

I have a couple of questions that i thougth this group could help me with. 1. A plane (SR71) takes off from the equator, with a lateral speed, relative to space of 1000mph. (earth rotational speed) say it takes an hour to get there so, its going 10,000mph or something. . Tt flys over the...

1. The problem A very simple question on a quiz given to me states that, "A 63 kg diver is standing on a diving board waiting to commence her dive. The diving board has compressed 0.08 m. Determine the elastic potential energy of the diver." 2. The attempt at a solution I thought this question...

Since the universe is expanding, photons emitted by distant stars are red-shifted, having their wavelengths stretched out. But, since the energy of a photon is dependent on the inverse of its wavelength, doesn't that mean that the expansion of the universe is causing photons to lose energy? How...

Homework Statement https://moodle.telt.unsw.edu.au/pluginfile.php/2296810/question/questiontext/2691158/6/1668509/cart%20track.png A block of ice (that we shall treat as a particle) slides with negligible friction or air resistance on the curved tpath sketched (black line). The mass of the...

From what I understand, there are 2 sets of fermions, one left-chiral and one right-chiral. Every electron in my body can be left-handed or right-handed. Do they stay the same forever or can they change chirality? Or is it more abstract property and a single electron can not be assigned...

Homework Statement Mechanical crane raises 225kg at a rate of 0.031m/s^2. from a rest to a speed of 0.5m/s over a distance of 4m. Frictional resistance is 112N. m1=225kg a1=0.031m/s^2 u1=0m/s v1=0.5m/s s=4m Fr=112N A. Work input from the motor B. Tension in the lifting cable C. Max power...

In classical field theory, translational (in space and time) symmetry leads the derivation of the energy-momentum tensor using Noether's theorem. From this it is possible to derive four conserved charges. The first turns out to be the Hamiltonian, and thus we have energy conservation. The...

Homework Statement Playing in the street, a child accidentally tosses a ball (mass m) with a speed of v=23 m/s toward the front of a car (mass M) that is moving directly toward him with a speed of V=20 m/s . Treat this collision as a 1-dimensional elastic collision. After the collision, the...

Homework Statement A 500g putty ball moving horizontally at 6m/s collides with and sticks to a block lying on a friction-less horizontal surface. If 25% of the kinetic energy is lost, what is the mass of the block? Homework Equations initial (i) = final (f) m1v1+m2v2 = m1v1+m2v2...

Homework Statement A spaceship of frontal area 25 m2 passes through a cloud of interstellar dust at a speed of 1.0x106 m/s. The density of dust is 2.0x10-18 kg/m3. If all the particles of dust that impact on the spaceship stick to it, find the average decelerating force that the impact of the...

Note: Please only give hints please! No answers because I want the satisfaction of solving it. 1. Homework Statement A mass M at height h above flat round and falling vertically with velocity v breaks up explosively into 2 parts. The kinetic energy given to the system in the explosion is E...

When an RF antenna absorbs a signal, the momentum is transferred in quantized photon-electron interactions. The electrons in the metal will be given both perpendicular momentum (the actual signal information) and momentum in the direction of propagation (shown below): The momentum in the...

I am not sure that I fully understand even the basic aspects of the Quantum measurement and entanglement but I just came across this thought experiment and I wish to resolve it. In a setting of two entangled spin-1/2 particles, suppose that Alice applies a uniform magnetic field ##B_0## along...

I have read that "Information is conserved", or at least that it should be. I read this in some discussion about whether or not black holes destroy information. (ref: Leonard Susskind, Stephen Hawking, The Black Hole War, etc..) It is believed systems in distinct states evolve into distinct...

When analyzing the conservation of angular momentum of a particular system, should we use the same p.o.r. before and after or can we use different p.o.r.'s? As far as I know, we should always use the same reference, but sometimes I see several solutions that use different references in my...

Homework Statement A block of mass 200g is suspended through a vertical spring. The spring is stretched by 1.0 cm when the block is in equilibrium. A particle of mass 120g is dropped on the block from a height of 45 cm. The particle sticks to the block after the impact. Find the maximum...

Homework Statement Consider a massive pulley of mass m and radius r shown in the figure below, with two objects hanging off it having masses m and 2m, respectively. The pulley can be considered as a uniform disk, and the string is massless, does not stretch and does not slip. By considering...

1. Homework Statement A toy car coasts along he curved track shown above. The car has initial speed vA when it is at point A at the top of the track, and the car leaves the track at point B with speed vB at an angle ϴ above the horizontal. Assume that the energy losses due to friction is...

Hello, A dude I'm discussing momentum and kinetic energy with says this: "Place two masses in deep space, the only gravitational attraction is from each other. One of the masses is ten kilograms and the other is one kilogram. From Newton's Third Law we know that the mutual attraction is equal...