Energy conservation Definition and 434 Threads

I have followed some of the previous posts on the topic , but the conflicting arguments have left more than confused. Consider this simple scenario : Two wave pulses on a string generated by identical sources but with a phase difference of 180 degrees meet and interfere destructively. For...

Homework Statement I know that this question has been dealt with on this forum before, however it is part (b) that is new and that I need help with. I have re-written part (a) for clarity. Question: The greatest instantaneous acceleration a person can survive is 25g, where g is the...

A ball A (mass ma) with initial velocity v colides with a ball B (mb) initially stopped. A and B gets the same direction/velocity v', Calculate v' By linear momentum conservation ma.v = (ma + mb).v' v' = mav(ma + mb) But by mecanical energy conservation ma.v²/2 = (ma +...

I'm sure someone has already thought of this somewhere, but can a wormhole violate the conservation of energy IF the object takes two paths? I mean like this: Imagine a wormhole near a charged object, one closer, the other farther. Then imagine the particle being attracted to the charged...

Hi everyone. I believe that I'm in the right place for this topic. If not, please excuse me for the misplacement :) I am a programmer, not a physicist, so please excuse my lack of knowledge. I currently need help with an energy conservation problem. I am currently working on this problem...

I've just read the FAQ about this and IMO it is "not even wrong" to say that energy conservation doesn't apply to Cosmology. The fact is energy conservation is clearly stated in the EFE by the vanishing divergence of the stress-energy tensor and since GR is the theory we currently use in...

Alright, this might sound stupid, but let us imagine a scenario. I bring an object from height 10 m to 4 m such that the velocity of the object remains constant. Due to this the potential energy of the object decreases. Now my question is, where does this energy go?

Homework Statement A 0.321-kg mass is attached to a spring with a force constant of 13.3 N/m. If the mass is displaced .256 m grom the equilibrium and released, what is its speed when it is .128 m from equilibrium. The answer is 1.43 m/s Homework Equations k=(w^2)m w=2pi/T The...

I want to know what exactly is the free-electron laser power beaming system that will be used in our future Space elevator and how the conservation of energy and momentum is associated with this project that NASA will launch. ? Other info: I am taking grade 12 university level physics; All...

The following thought/problem recently hit me: What the hell happens to photon energy lost due to the cosmological redshift?

Hello everyone! I've found this problem in my exercises book, and I'm having slight troubles solving it. "Consider a simple pendulum with mass m, on a string with l length. Considering that the position of pendulum is determined with the angle \theta and noting that the string DOES NOT do any...

For energy conservation does it apply to both conservative and non conservative forces?

Imagine you have a wind turbine that was connected to some sort of device. say a freaking massive, high energy using blender. Now there was a constant breeze blowing across the wind turbines, in the same direction resulting in a uniform amount of power being produced by the turbine. The...

A capacity(C) connects directly to a constant source(E); total resistant is zero. When the capacity has been charged already, it has energy :1/2CE^2. The work done by the source is CE^2. Comparing two of them leads to an error of the energy conservation equation. What's wrong with it? When...

Homework Statement This is a theory question that has puzzled me for a long time: Two waves of exactly the same amplitude, and exactly opposite phase and opposite velocity are traveling toward each other through some medium such as a rope, a slinky, or whatever. They meet and interfere...

Homework Statement A 0.80-kg block is held in place against the spring by a 67-N horizontal external force. The external force is removed, and the block is projected with a velocity v1 = 1.2 m/s upon separation from the spring. The block descends a ramp and has a velocity v2 = 1.9 m/s at the...

When do i know which component of velocity to use when an object is shot at an angle? For example: a ball of given mass is shot 32degrees above the ground with Vinitial of 74m/s. In using conservation of energy, K.E. = .5 mv^2 , which velocity component do i use?

Homework Statement My teacher told me that this will be the general equation that we will be using. My question is how do I know what to cancel out given a problem? I don't even know what these variables mean. I was absent during the intro of this lesson and I need a quick answer. Thanks...

Hello, I nowhere find general form of energy conservation law, but in one book i found this (*)\hspace{1cm}E=E_{in}-E_{out}+E_{generated} where E(in) is energy flow into system, E(out) is energy flow out of system and E(generated) is energy generated. It was in sense of heat...

Homework Statement A 35-g ice cube at 0.0 C is added to 110 g of water in a 62 g aluminum cup. The cup and the water have an initial temperature of 23 C. a. Fine the equilibrium temperature of the cup and its contents b. Suppose the aluminum cup is replaced with one of equal mass made...

Hi there, I'm studying for mechanics final and I came across a question I can't figure out how to do. The question is as follows: A person is on a sled of mass 10 kg that’s moving to the right on a frictionless surface at 4 m/s. Just before the sled goes down a hill the person of mass 50 kg...

Homework Statement the small mass m sliding without friction along the looped track is to remain on the track at all times, even at the very top of the loop of radius r. a) calculate, in terms of the given quantities, the min. release height h. if actual release height is 2h, calculate...

JO is "loaded" into a spring-loaded "cannon-ball" launcher as PICTURE. She lands into a springy trampoline that is initially at ground level. THe Earth is dug out under the trampoline so that when she lands, the trampoline will compress below ground level. At position 1, 60kg JO is at rest...

Homework Statement A block of mass 7.00×10-1kg is suspended by a string which is wrapped so that it is at a radius of 6.00×10-2m from the center of a pulley. The moment of inertia of the pulley is 5.70×10-3kg*m2. There is friction as the pulley turns. The block starts from rest, and its speed...

Homework Statement An 8.77-kg block slides with an initial speed of 1.58 m/s down a ramp inclined at an angle of 28.5° with the horizontal. The coefficient of kinetic friction between the block and the ramp is 0.69. Use energy conservation to find the distance the block slides before coming to...

Hello all. I was watching the prof. Susskind lectures on YouTube. I'm very grateful to Stanford and the professor for making that knowledge so easily available to people willing to learn. While I did understand almost everything said I still have some question of things that I did not...

Please teach me about this question: In a process of scattering of closed system of particles(in point of view of quantum field theory),the Lagrangian of the system is not invarian(up to 4-divergence) under time translation.So that following the Noether theorem,the energy of the system is not...

Homework Statement Two protons (radius 10^-15 m) are headed directly toward each other with equal speeds. Use the principle of energy conservation to compute the minimum kinetic energy and initial speed each proton must have if they are to collide. Homework Equations W = delta K W =...

Homework Statement A ball with a mass m swings from a string of length L from a pivot. A distance D directly below the pivot there is a nail. The ball is released making an angle theta=pi/2 with the vertical. For this particular problem, there is no friction. Assuming the ball swings...

[Two ball of mass 60g are attached with mass less rubber thread and held in vertical position as show in figure. In this position length of rubber thread is 40cm and it is not stretched. The upper sphere is slowly raised vertically upward until the lower ball just becomes unsupported by ground...

I am sure this question comes up frequently in the forum, and I have read a number of answers to it in different places; namely, that since the expansion of the universe stretches the wavelengths and thereby lowers the energy of light, what happens to the principle of the conservation of Energy...

I want to discuss energy conservation and time dilation relative to the cosmological redshift. Because the elements of the redshift are coordinate specific, I’ll focus just on the FRW metric using proper distance coordinates (not comoving coordinates). As explained in Tamara Davis’s cover...

Homework Statement A 2.1 x 10^3kg car starts from rest at the top of a 5.0m long driveway that is inclined at 20degrees with the horizontal. If an average friction force of 4.0 x 10^3N impedes the motion, find the speed of the car at the bottom of the driveway. Homework Equations...

Is photon energy conserved for comoving observers in redshifted light from receding galaxies? And in the case of gravitational redshift? Thanks

Hi there. I am having trouble finding an explanation with waves. Suppose that you have to sinusoidal waves y1=Asin(kx-wt) and y2=Asin(kx-wt+phi) If we add them up, the resulting wave will be y=2Acos(phi/2)sin(kx-wt+phi/2). Now, if phi equals pi then the resulting wave will have no...

how does the lenzs law relates to the law of coservation of energy ?

Homework Statement A string exerts a tension force of 55N on a 10kg block as it moves a distance of 5m up a frictionless incline. The string pulls parallel to the incline. A) Find the total external work done on the block-earth system as the block moves 5m up the incline. B)Find the...

Let's consider a water dispenser which use as input water at room temperature and the electrical energy to make the water cold and on the other side, hot. If you combine the cold and the heated water to obtain the water at the room temperature again, in which the electrical energy transform...

Case:1 I have one iron spring. I compress it gives potential energy E= ½* K*x2 & bind it by glass wire which is not melted in acid. Now I put this spring in acid & it melted completely, So where the potential energy gone? Case:2 I put one magnet in glass vessel & hold it in vessel by some...

This is question about equation E=m*c2. Why this equation does not required any condition of matter? Case 1: I take two mole (4 Kg)H2 & one mole(32 Kg)O2 & make water & get energy. 2H2 (4 Kg Hydrogen)+O2 (32 Kg Oxygen)=2H2O(36 Kg of water)+ 572 KJ Energy Now I convert this water into energy...

Hi, I'm trying to convince myself (mathematically) that energy is conserved at the vertex in e^-e^+ annihilation, while solving Exercise 3.5(b) of Halzen and Martin's book (page 83). I am looking at the time dependent term in the scattering amplitude T_{fi} alone, to recover the delta...

when an electron neutrino is produced in the sun, it have the total energy of E. the total energy E have the relation with mass and momentum as E2=p2+m2. during the journey of its propagation from sun to earth, the electron neutrino change their flavor to muon neutrino which have mass m'...

Homework Statement Question for search purposes: A crate is placed against a compressed spring on an incline. When the spring is released, the crate moves up the ramp and comes to a stop. How far was the spring compressed? Hint: The mass and the spring may not be in contact at the end.

Homework Statement Using x(t)= A cos(wt+phi) verify that the total energy is conserved. Homework Equations V(x)= Integral x to x1 F(x)dx The Attempt at a Solution I thought about using the aboved equation but have no idea where to start.

Homework Statement In proton-beam therapy, a high-energy beam of protons is fired at a tumor. The protons come to rest in the tumor, depositing their kinetic energy and breaking apart the tumor’s DNA, thus killing its cells. For one patient, it is desired that 0.10 J of proton energy be...

Hi,all, can anyone help to understand how uncertainty principle consist with energy conservation? dEdt >= h/2, then in a short time interval, the energy can be really large, even the previous state has lower energy? I can't really understand this.. say, particle A appeared at t=0 (at...

Consider a 4 dimensional spacetime which is everywhere flat and is closed in along all three spatial dimensions. Since spacetime is everywhere flat we can use global inertial frames. We will not consider any gravitational interactions in this problem. Now a valid vacuum solution to maxwell's...

How is energy conserved in an expanding universe? As space expands between, say, stars in a galaxy, don't they gain potential energy in the gravitational field of the galaxy? Which mechanism lessens the total kinetic energy?

hi, i am preparing for an exam and i am really clueless about this one. an image is attached. The left side of the figure shows a light (`massless') spring of length 0.260 m in its relaxed position. It is compressed to 78.0 percent of its relaxed length, and a mass M= 0.150 kg is placed on...

Homework Statement I just came across this question and i think its giving me a real hard time. This is part of a bigger question so I'll provide the other statements below 7 The maximum height reached by the ball is approximately (1) 1.2 m (3) 4.9 m (2) 2.5 m (4) 8.5 m Homework Equations t=1...