Conservation Definition and 999 Threads

Are there situations when conservation of Energy does NOT apply? Thanks.

Homework Statement Homework EquationsThe Attempt at a Solution 4a at x=-2 F=0N Potential energy=integration of F(-2)=Integration of 0=0 so it will reach minimum at x=-2? b. integration of F(-2)-integration of F(-2-h)=m(v-0)^2/2 am i right? 5 Centripetal force=mv^2/r=mgsinθ-Fn(normal force)...

Homework Statement Homework EquationsThe Attempt at a Solution I know that the velocity of mass at the bottom of the swing is V = Sqrt(2gh), but I'm not sure how to get from there to the velocity of A. Is it as simple as Angular momentum of B = Linear Momentum of B?

Homework Statement A block of mass ##m## slides down a wedge of mass ##M## and inclination ##\theta## whose surfaces are all frictionless. Find the velocity of the block when it just reaches the bottom of the wedge. Homework EquationsThe Attempt at a Solution I was told that to solve this...

I was hoping to learn a little bit more about matter-antimatter annihilation. As I understand it, when a particle meets an antiparticle, they are both annihilated and energy is produced. Does this contradict the laws of conservation of energy and conservation of matter? I haven't had much luck...

Homework Statement A child with mass m is standing at the edge of a merry go round having moment of inertia I, radius R and initial angular velocity x as shown. (The figure shows a disc moving anticlockwise, with the velocity v (Mentioned at the end) pointing upwards to the right most edge of...

As i am a physics amateur and most of what i learned is through videos, i sometimes get confused about energy conservation, my question concerns particle acceleration in CRT for example, we create a potential difference ( which requires energy) between the anode and the cathode, then the...

Homework Statement "identify the type of energy conversions present in each of the following situations. Some questions may use multiple types of energy." 1) a wind turbine producing electricity 2) two children sliding down a hill on a toboggan 3) a toaster oven browning a bagel Homework...

Homework Statement a trailer with a mass of 150 kg happen to roll away with the speed 20 m/s. 450 kg cement fall staight down into the trailer! which speeds does the trailer get when the cement fall into it? Homework Equations [/B] I know how to solve it but I don't know why it works. Is...

Hi guys! one quick question, if in a quantum system the hamiltonian of a particle evolves with time (let's say, the potential is a function of t), the energy is not conserved right? I just want to be sure about this, thanks!

Homework Statement An alpha particle is a nucleus of helium. It has twice the charge and four times the mass of the proton. When they were very far away from each other, but headed toward directly each other, a proton and an alpha particle each had an initial speed of 3.6×10−3c, where c is the...

In Lagrangian mechanics the energy E is given as : E = \frac{dL}{d\dot{q}}\dot{q} - L Now in the cases where L have explicit time dependence, E will not be conserved. The notes I am referring to provide these two examples to distinguish between the cases where E is energy and it is not...

Homework Statement Two discs of different radii and masses are kept on a smooth horizontal table and both are free to rotate about their fixed central vertical axis. One of them is given some angular velocity while other is stationary. The rims are brought in contact. There is friction between...

I did a problem a coule of weeks ago with a vertical rod, frictionless hanging around the upper end, length L and mass m. Then a bullet with the same mass, m speed v is fired horizontally at the lowest point of the rod and becomes embedded in the rod. So I calculated the maximum angle it would...

So, I'm trying to think of some way to formulate a "Conservation of Symbols" Law of Mathematics. Something like this: By "symbol" I mean any atomic variable, constant, digit, operator, bracket, etc., that is present in a syntactically correct expression, equation, or inequality. So the...

Homework Statement Hi everybody, I was studyng a photon disintegrating in one electron and one positron in the presence of a heavy atomic core; I want to find the final momentum of the atomic core Homework Equations Conservation of energy: Eγ=2me+Sqrt(Mn2+Pn2) Conservation of momentum Pγ=Pn...

Homework Statement Two identical buggies 1 and 2 of mass ##M## with one man of mass ##m## in each, move without friction due to inertia towards along two parallel rails. When the buggies are opposite to each other, the men exchange positions by jumping in a direction perpendicular to motion of...

Does energy conservation law still hold if the system contact with varying source of energy? Because in QM the Hamintonian of the system always commune with itself,so the conservation law still correct.But if it is,where is the exchange energy between the system and the enviroment?

Hi, Some "derivations" of the law of the lever argue with conservation of energy: If one arm of the lever of length ##r_1## is pulled by a distance ##s_1## with force ##F_1##, the other arm moves by a distance ##s_2=s_1 \frac{r_2}{r_1}##. From conservation of energy ##E=F_1 s_1=F_2 s_2## it...

Suppose a block of 10kg at 10m/s collides into a block of 5kg at 0m/s. Does a given percent of energy loss in the collision affect the final velocity of the blocks after the collision? For instance, if there is no energy lost in the collision, would the final velocities be faster than if...

Homework Statement [/B] Conservation of momentum of x components 10(20Cos(-30)) + 5(5Cos60) = 10v_{f}Cos(α) + 5v_{f}Cos(β) 185.7 = 10v_{f}Cos(α) + 5v_{f}Cos(β) Conservation of momentum of y components 10(20Sin(-30)) + 5(5Sin60) = 10v_{f}Sin(α) + 5v_{f}Sin(β) -78.3 = 10v_{f}Sin(α) +...

Homework Statement Given a reference frame O' moving at a constant speed $\vec{V}$ in relation to another reference frame O, I want to prove that ##\vec{r_{1B}} \times m_1\vec{v_{1B}} + \vec{r_{2B}} \times m_2\vec{v_{2B}} = \vec{r_{1F}} \times m_1\vec{v_{1F}} + \vec{r_{2F}} \times...

In Kip Thorne’s “Black Holes and Time Machines”, he outlines objections to using traversable wormholes, if they existed, as time machines, the main one being (roughly) that radiation could also time travel, and mount up to destroy the wormhole. But isn’t another objection the conservation of...

Hi, I googled 2d elastic collisions to see if I could find a problem where two objects are approaching each other from different directions before collision and then moving away from each other at different directions after collision, but I noticed that all the problems I've found have 1 of two...

Homework Statement [/B] A sphere of radius $1m$ and mass $25 Kg$ is put on another sphere of radius $5 m$ and $7 Kg$ which is placed on a smooth ground. Now the upper sphere is pushed very slightly from it's equilibrium position and it begins to fall. Now when the line joining the centre of...

Does the relativity of simultaneity imply the impossibility of non local conservation laws?

Homework Statement Figure shows a massless wheel of radius R on which at a point a mass m is fixed and a uniform chain of mass 2m is tied to it which passes over the rim of the wheel and half of its length is hanging on other side as shown in the figure. When a small clockwise jerk is given to...

Homework Statement Three identical balls (of equal masses) are connected by light inextensible strings and kept on a smooth horizontal surface. The middle ball B is given a velocity ##v_0## at ##t=0##. Find the velocity of ball A when A collides with C. Homework Equations Impulse ##J=\Delta...

Searches of PF archives for Information Conservation turn up many threads in which the question is more or less dismissed. It sounds like many PF regulars don't believe in it, as if it were fringe science or metaphysics. Contrast that with the prominence given to the recent thread Stephen...

I know gravity is a conservative force field and can be treated as such for all intents and purposes, but I was just thinking that in order to show that a vector field is conservative that vector field must be defined everywhere (gravitational force field is not defined at r=0). I was thinking...

So consider a theory of a complex scalar field ##\phi## with a global U(1) symmetry ##\phi \rightarrow e^{i\theta} \phi##. The theory admits a conserved current $$ J^\mu = \frac{\partial \mathcal{L}}{\partial (\partial_\mu \phi)} \delta\phi + \frac{\partial \mathcal{L}}{\partial (\partial_\mu...

Homework Statement A 9.1 g ball is hit into a 98 g block of clay at rest on a level surface. After impact, the block slides 8m before coming to rest. If the coefficient of friction is 0.60, determine the speed of the ball before impact Homework Equations Ek+1/2 mv^2 Ff=uFn The Attempt at a...

Homework Statement A paintball gun launches a paintball off a cliff at an angle of elevation of 45°. The cliff is 165 m high. The paintball is initially moving at 180 m/s. Calculate the speed of the paintball as it hits the ground. I'm having trouble understanding how to solve this, I have...

In my intro to Quantum Mechanics course, my professor gave a little aside while exploring the analogy between the Schrodinger Equation and Newton's second law: in classical physics, energy is conserved when the potential energy is not a function of time. I wanted to try to answer this my self...

Homework Statement hello. i tried to solve for the problem, which was quite difficult for me and I'm not sure whether i approached it correctly, so if someone will help me figure it out thank you! the problem: 1. a 2 kg firework is shot vertically, at v=50 m/s a. what is the velocity and...

Assuming R-pairity and thus the creation/destruction of supersymmetric particles happens in pairs, how is angular momentum conserved when a particle and its supersymmetric partner have different spin by 1/2?

I am unclear about this law of the conservation of baryons; does it mean that the number of leptons can change OR the number of baryons but not both? Also, does it mean that no experimental evidence shows that baryons can decay into mesons. Can someone state clearly the law of conservation of...

I would like people's opinions on why the negative energy solutions of Dirac's Relativistic Wave equation were simply ignored in 1934 to make things fit. Another related question is with the energy conservation laws as they stand. Why in pair production from a photon at 1.022MeV forming a...

Homework Statement During an explosion, a bomb explodes into 3 pieces. Two fragments, whose masses are 0.8kg and 0.5kg fly off with velocities of 10m/s and 16m/s respectively along the paths at right angles to each other. If the third fragment goes off with a velocity of 24m/s, then find its...

Homework Statement A small mirror of area A and mass m is suspended in a vertical plane by a weightless string. A beam of light of intensity I falls normally on the mirror and the string is deflected from the vertical by a very small angle A. Assuming the mirror to be perfectly reflecting, to...

The decay \rho^0 \rightarrow \pi^- \pi^+ occurs with a probability of 100\%, whereas the decay \rho^0 \rightarrow \pi^0 \pi^0 does not occur in nature, due to isosphin conservation. I don't understand this. Looking at the Isospin and its third component ¦I,I_3\rangle we have in the first...

Energy of beta ray and neutrino is equal Q=M(mass) of nucleous before-M of nucleous after,so it about 1Mev.But the mass of W boson is 80 MeV,so the least energy of electron and neutrino must be 80 MeV. Why there is the difference?Why does it seem that energy were not conservation?

Homework Statement : [/B]I just have a quick question about direction of velocity in solving for energy conservation problems. Since energy has no direction, do different angles ever affect the outcome? Like say in a collision where a truck hits three other vehicles and sends all three in...

I know a similar question has been asked but I'm still kind of stumped. Imagine the Earth on the left and a small mass to it's right separated by some distance h. You are in the frame of reference where the Earth and the small mass are moving to your right at some speed v. So, both the Earth...

Krichhoff's voltage law (kvl) is said to be conservation of energy but i couldn't get a satisfactory explanation for that, i want to say - say, we have a simple circuit consisting of a battery(of emf E) and a resistor(of resistance R), so having connected them by ideal wires, we have electrons...

Krichhoff's voltage law (kvl) is said to be conservation of energy but i couldn't get a satisfactory explanation for that, hence i tried of thinking one but i doubt its validity, my instructors at collage thought of it as something useless , i couldn't understand them ! I think somebody here can...

Homework Statement Im stuck on this question please help. =/ a 50.0g bullet travels right and becomes embedded in a 7.00kg stationary block. the block and embedded bullet moves off at a velocity of 5.00m/s right. what was the initial velocity of the bullet? the answer is 706m/s right. Homework...

A person has reached H height by 100J energy whereas by the use of pulley, the man can reach the height by a fraction of that energy. In this manner, it is reaching height H by giving off less energy than required by gravitational potential energy. So isn't the law of conservation of energy...

Okay, so I've had this question on wormholes which seems to have hijacked my mind from some time now, and what better place to bring it out rather than PF? A previous thread containing lots of lengthy posts was made here a few years ago, but I'm not getting a clear-cut answer despite leafing...

So my question is when to apply conservation of angular momentum?When there is no external force ,right?But in the case below A mass m moves in a circle on a smooth horizontal plane with velocity v0 at a radius R0. The mass is attached to a string which passes through a smooth hole in the plane...