Conservation Definition and 999 Threads

Skip to 29:50. Here Feynman is explaining how some laws are not independent of energy conservation. In this case he goes on to explain how instead of using the law of levers were can use energy conservation to see what weight an object needs to on one side be to balance (or be in a state where...

Homework Statement This is my first time posting here guys so correct me if I am wrong. This question was on my test and I wanted to know if I did it right. There is a block of mass m and it is moving at a certain velocity before pressing against a spring which compresses distance x. Find...

Do temporary dipole moments require energy to form? I'm talking about Van der walls and London forces. If temporary dipole moments don't require energy to form then consider the free electrons in a metal plate, temporary dipole forces in the metal act on the free electrons causing them to gain...

Homework Statement Hey everyone! I'm new to these forums so I apologize in advance if I do something wrong! I just had a quick question about the momentum in one direction equation m_1v_1o +/- m_2v_2o = m_1v_1f +/- m_2v_2f; I'm just not sure when I'm supposed to add these values and when I'm...

In mutual induction, when a coil is turned on or off, it generates voltage in another nearby coil. But where is that voltage coming from? It can't be created, so what form of energy does it convert from? As far as I know, when the magnetic field cuts across the coil, that generates voltage...

OK, so I'm right in the middle of watching Interstellar and I've just seen the part where they have docked with the 'mothership' and they fire up their engines to get it to rotate. This is so they can generate a centrifugal force to simulate gravity. My question is - first the ship was not...

I am confused about the current physics regarding neutrinos and implications about the conservation laws of mass-energy and linear momentum. I have read the threads listed for similar discussions, including, "How does conservation of energy/mass apply to neutrinos?", and none of them seem to...

Homework Statement An astronaut is pushed from her ship at a velocity of 2m/s. Her weight including her tool belt is 120kg. Remembering Newtons 3rd law, she takes 5 seconds to decide to detach her belt and throw it away from her. The 20kg tool belt leaves her suit as she throws it in front of...

Homework Statement One end of a spring is attached to a wall to a block of mass X= 2kg (on a frictionless horizontal table). Another mass M of 150g moving at a speed of 7m/s collides (inelastic). This takes 0.4s to compress the spring to its max compression. I have to find the max force of...

Suppose we have an electric field, and push a proton or electron through it (from rest). We're accelerating it through an electric potential difference of some kind. Why do we apply conservation of energy to the particle-field system to find the speed of the particle? Example: Calculate the...

Homework Statement A flywheel and shaft have a moment of inertia of 600kg and is rotating at 5 rev/s. Another flywheel and shaft, on the same axis, is suddenly connected by means of a clutch. If this flywheel and shaft has a moment of inertia of 620kg and is initially at rest, calculate: a)...

What ensures conservation of energy and conservation of momentum in Electron-Positron annihilation? If e=mc2 and momentum = mass*velocity, couldn't the energy equivalence of the electron and the positron be converted to make one photon, or more that 2 photons? I've read that two photons are...

Hello folks. This is Sandeep. I have many lingering doubts in physics that I am here to get cleared. This has become more of an issue ever since I decided to teach physics to my young nephew. My first question pertains to electromagnetic waves and the conservation of energy. Consider an AC...

Hey! :o I am looking at the conservation of momentum. The force at $W$ from the tensions at the boundary $\partial{W}$ is $$\overrightarrow{S}_{\partial{W}}=-\int_{\partial{W}}p \cdot \overrightarrow{n}dA=-\int_{W}\nabla p dV$$ where $p(\overrightarrow{x}, t)$ the pressure and...

Hi All, Is the Angular momentum conserved at the singularity ? Thanks in advance

Define energy as E=T+U. For anyone using different terminology, by rheonomic (time dependent constraints) I mean that if a system has N degrees of freedom, the position vectors of each particle of the system are given by ##\vec{r}_i(q_1,q_2,...,q_n,t)##. Where ##q_i## are generalized...

Hi I recently got some weird feedback on homework. It said that "..momentum is only conserved componentwise..". The problem involved Compton scattering, and I had used p_{\lambda,1} = p_{e,2} + p_{\lambda,2} to find p_{e,2} for collision between an electon and a photon. I had used the...

Homework Statement Can you change the system (as you would in a work/energy problem) so you can get rid of all external forces in a momentum problem for example by making your system the earth, a mass, and a spring (if the problem involved those 3 objects)? Homework Equations P=mv[/B]The...

Homework Statement A 2 kg frictionless cart with a velocity of 6 m/s hits a wall and rebounds with a velocity of 4 m/s. What is the impulse on the cart by the wall? Is momentum conserved? Homework Equations J = Δp The Attempt at a Solution J = Δp = pf-pi = mvf-mvi = 2kg (-4m/s -6m/s) = -20...

Throwing a ball which is (m)kg on the ground If the velocity of the ball just before it reaches the ground is (v)m/s Assume it is a elastic collision The velocity of the ball when it leaves the ground should be (-v)m/s According to conservation of momentum,the ground has a change of...

So I've found several instances in which Bernoulli and Conservation of momentum (in Reynolds transport theorem form) give different answers for the study of an inviscid fluid. Let's consider a simple situation as described in my diagram attached. Basically a tap/faucet is releasing fluid, which...

In section 19.5 of Peskin it is stated that if a scale transformation ##\varphi \rightarrow e^{-\sigma}\varphi(xe^{-\sigma})## is a symmetry of a theory then there is a current ##D^{\mu} = \Theta^{\mu\nu}x_{\nu}## (here ##\Theta^{\mu\nu}## is the Bellifante energy-momentum tensor) with...

Hi all, I am trying to follow the calculation by samalkhaiat in this thread: https://www.physicsforums.com/threads/finding-equations-of-motion-from-the-stress-energy-tensor.547502/page-2 (post number 36). I am having some difficulty getting the equation above equation (11) (it was an unnumbered...

In a reversible carnot cycle the amount of heat added is always more than the amount of heat taken out. So why doesn't it explode? I'm wondering how heat is conserved mathematically as the area under the curve of a p-v diagram. u=q+w. If the heat during expansion is always more than the heat...

Consider the flat FRW metric in Cartesian spatial co-moving co-ordinates: ##ds^2=-dt^2+a(t)^2(dx^2+dy^2+dz^2)## As I understand it, since the metric does not depend on the the spatial co-ordinates, there exist Killing vectors in the ##x##,##y##,##z## directions. Does this imply that the...

The Einstein field equation is inconsistent unless we demand a divergence-free stress-energy tensor. This makes me think that Hoyle's steady-state cosmology is inconsistent with general relativity. But Hawking and Ellis has this at p. 90: I had always imagined that the C field was just some...

if a nice fuzzy block is stationary on a frictionless surface and is hit by a high velocity bullet in such a way that the bullet cleanly penetrates and exits the box leaving the box stationary but the velocity of the bullet slightly changed, what can one say about the conservation of momentum of...

When temperature of the universe falls below nucleon mass ##T<<1## GeV, the number densities of nucleons (proton and neutron) which are in kinetic equilibrium can be obtained as ##n_i=g_i (\frac{m_i T}{2\pi})^{3/2} e^{\frac{\mu_i-m_i}{T}}##. Since baryon number should be conserved, then I...

Homework Statement Question: Figure 1: QUESTION ABOVE. Homework Equations The Attempt at a Solution :[/B] P + P → K+ + K- + P + P Firstly, I just wanted to check that this is correct. I found the answer pretty quickly by googling it but have since spent a long while trying to understand...

Homework Statement A stationary atom releases a photon when it goes from excited state n to lower state n. Delta(E) is the energy difference between initial state En and final state En', consider kinetic energy of recoiling atom. Apply conservation of energy and momentum and solve for the...

Hi, so my question is along the lines of the following: Since the strong and EM forces are mediated by massless exchange particles, due to Heisenbergs uncertainty principle these forces are long range. Well, ok. But the weak force is mediated by W and Z bosons which are massive hence they can...

Hey everyone, I have a little physics space problem I can't manage to solve, so I hoped someone would be able to help me here. This is the problem: We have an object with mass m and speed v1 approaching an other object with mass M and speed U1. The two objects are moving in opposite direction...

Assume there is a table with an infinite long wire passing through the centre and few iron pieces lying around the wire on the table. Now I pass current through the wire which creates electro magnetic field due to which all the iron particles get magnetic potential energy. They are attracted...

Question:- A bead slides without friction around a loop-the-loop (Please click on the below link for diagram). The bead is released from a height h = 3.50R. (a) What is its speed at point A? (b) How large is the normal force on it if its mass is 5.00 g...

Question with diagram: Relevant equations: Attempt : My question: Using my method I got the wrong force , not sure if in this situation I can use Q=A1U1 = A2U2, hence maybe that's why U2 = 195 m/s looks wrong/too fast? I continue to use momentum conservation in the x and y directions...

In Leonard Susskind's the theoretical minimum, he says, "For any system of particles, if the Lagrangian is invariant under simultaneous translation of the positions of all particles, then momentum is conserved". For a system of two particles moving under a potential which is a function of the...

I have question that I've been thinking about for some time now, and that I can't get my head around. I an experimentalist without education in quantum field theory, and my quantum mechanics introduction courses were a long time ago, so bear with me please. As far as I understand, neutral kaons...

Homework Statement A ball (m=0.7kg) is dropped from a height (h=30m). The air resistance force is given by the formula F=kv^2 where k=0.0228 and v is the ball's speed. The ball bounces after a perfectly elastic collision. Calculate the maximum height the ball reaches after the collision...

Homework Statement A firework at rest with a mass of 0.90kg explodes into 3 pieces. One piece has a mass of 0.25kg and moves horizontally at 36m/s [N]. Another has a mas of 0.35kg and moves horizontally at 32m/s [S50°W] Find the velocity of the third peice[/B]Homework Equations SOH CAH TOA...

I am confused about how the principle of conservation of energy can be used to predict the velocity of a pendulums for any given height and angle. For example, say I use the equation U = -K (potential is equal to kinetic) to solve for the velocity at 15 degrees of a pendulum bob whose wire...

Once we define energy and momentum carried by the field , is it possible to derive Maxwell's equations from conservation of momentum and conservation of energy (along perhaps with conservation of charge)?

Homework Statement A bird m_b=0.470kg, is flying horizontally at v_b=2.50 m/s, not paying much attention, when it suddenly flies into a stationary vertical rod, hitting it d=25cm below the top. The rod is uniform, L=0.740m long, has a mass of m_r =1.60kg and is hinged at its base. This time the...

Homework Statement Homework Equations KEi = KEf The Attempt at a Solution since it is perfectly elastic, kinetic energy before = kinetic energy after (1/2) (m) (20m/s^2) = (1/2) (2m) (VBeamf^2) + (1/2) (m) (VBlockf^2) is this the right approach? [/B]

Homework Statement There are two trolleys traveling in the same direction which are about to collide. Trolley 1 is traveling at 4 metres per second and has a mass of 2kg The other, Trolley 2, (which is in front) is moving a 1 metre per second and has a mass of 4kg. After the impact, they...

Homework Statement A lorry of mass 20,000kg is traveling at 20.0 metres per second. A car of mass 900kg is traveling at 30.0 metres per second towards the lorry. What is the magnitude of the total momentum? 1. 209 kNs 2. 373 kNs 3. 427 kNs 4. 1045 kNs 2. Homework Equations Linear Momentum...

Homework Statement *All units given are in standard SI units unless otherwise specified.* *Assume a closed system* How much of -200ºC Liquid Nitrogen is required to completely freeze 200mL (0.2kg) of pure liquid water at 0.00ºC (No change in heat, only a change in state)? Given Values. n=...

Hi. Let's say two monochromatic laser beams superimpose in a single point in space in such a way that there's constructive interference. Because there's constructive interference there, the total intensity at that point will be larger than the sum of the separate intensities. Will this mean...

Homework Statement Cart 1 and cart 2 are initially at rest, and after the explosion the momentum of the two carts was the same. If the two carts were moving at some initial speed v0 before the explosion: would the momentum of the two carts still be equal? Homework Equations Momentum. mvi=mvf...

Homework Statement Hey folks, anyone who can help me with this one get a massive shoutout. Here goes: 75 kg of water at 45 degrees celsius is "mixed" with 70 kg of Aluminum at 2600 Degrees Celsius. What is the final state of both system and how much, If any, of liquid water will be left Assume...

This is a study that was published in the New England Journal of Medicine done on the safety of e-cigs or better known as vaping. The article states, "They found that vaping 3 milligrams of e-cigarette liquid at a high voltage can generate 14 milligrams of loosely affiliated or "hidden"...