Conservation of energy Definition and 1000 Threads

  1. D

    Conservation of energy interpretation of percentage conserved

    Homework Statement I get that less percentage energy is conserved from potential to kinetic energy by measuring h and v with two balls for the heavier ball. I am trying to sort of why actually is like that! Two balls where dropped down from a ramp with different masses and volume. The smaller...
  2. Dennydont

    Photon colliding with stationary mass

    Homework Statement A photon with energy E collides with stationary mass m. They form a single particle together, what is this new particle's mass and what is its speed? Homework Equations Energy-momentum 4-vector P=(E, px, py, pz) Possibly P2=m2 The Attempt at a Solution Using 4- momenta, the...
  3. S

    Conservation of Energy Question

    Having problems with part (c) here, question is attached below in full. Homework Statement Using the equation 1/2 * Load * Displacement = Sum of (P^2 * L/2AE) From the past questions I have the following info, these are also included in the solutions so are accurate: A = 1x10^3 m^2 FAB =...
  4. P

    Conservation of Energy and General Relativity

    I was reading through some main stream scientific literature, and I came across Sean Caroll's "Energy Is Not Conserved" post. Essentially, he contends that through general relativity energy is not conserved, at least not in conventional manner of thinking about energy. Anyways, some portions of...
  5. L

    Conservation of energy and space expansion

    This had me thinking for a while. Imagine a photon emitted by a very distant object at a redshift of z = 2.0 for example. As the photon travels through space, due to space expansion the photon's wavelength will shift towards red. With an increase in the wavelength there must come a decrease in...
  6. S

    I Don't agree with law of conservation of energy

    Well this question has been in the mind since a long time. I believe that the law of conservation of energy is not true. If it is/was true then why would the universe expand and into what is it expanding ? obviously energy is created when the universe expands into "NOTHING". I will be waiting...
  7. REVIANNA

    Energy and momentum conservation

    Homework Statement [/B] A block of mass m is attached to a spring with a force constant k, as in the above diagram. Initially, the spring is compressed a distancex from the equilibrium and the block is held at rest. Another block, of mass 2m, is placed a distance x/2 from the equilibrium as...
  8. T

    Is Conservation of Energy the Key to Solving This Tricky Problem?

    I find this problem kind of tricky. I think it must be a, since a change in momentum of the car causes the same change in momentum of the earth.
  9. DoobleD

    Conservation of energy and momentum transfer

    Let's say a tennis ball with velocity with only an horizontal component hits a vertical wall at rest. After collision, conservation of momentum tells that : m_{wall}v_{wall} = 2m_{ball}v_{ball} Thus, the wall has now a (tiny) velocity and kinetic energy : v_{wall} =...
  10. S

    Conservation of Energy in a Pulley System

    Homework Statement Two masses are connected by a light string passing over a light, frictionless pulley, as shown in the figure below. The mass m1 (which is greater than m2) is released from rest. Use the isolated system model to answer the following. In terms of m1, m2, and h, determine the...
  11. TheDemx27

    Conservation of Energy vs Conservation of Momentum problem

    Homework Statement We are trying to find out whether we can hit a weight ##m=3## kg up to a given ##h=15.24## meters with a hammer with a head of ##m=6## kg swung at ##v=10## m/s. Homework Equations KE=0.5mv^2 PE=mgh p=mv The Attempt at a Solution One solution is to even see if the energy...
  12. faradayscat

    Dynamics/kinematics of rotating sphere

    I'm wondering about how one would describe the dynamics of a rotating sphere. Consider this: a solid sphere of mass "m" and radius "r" is set to rotate about a tangent to its surface. If it is released from the horizontal position such that it swings like a pendulum, what would be the force...
  13. dwdoyle8854

    Classical Dynamics -- Falling chain and energy conservation

    Homework Statement The statement of the question is:A chain of uniform linear mass density ##\rho##, length ##b## and mass ##M## hands as shown in the figure below. At time t=0, the ends A and B are adjacent, but end B is released. Find the tension in the chain at point A after end B has...
  14. E

    Easy conservation of energy problem? (long jump)

    Homework Statement m(person) = 60kg v1 = 3.0m/s v2 = 0 d = 2m y1 = -1m y2 = 0 A person is completing a long jump. At event 1 they are 1m in the air and are moving at a rate of 3.0m/s. At event 2 they are at rest on the ground, 2m from their initial landing place. What is the stopping force...
  15. physics411

    Conservation of Energy of cart Problem

    A 1.2 kg cart slides eastward down a frictionless ramp from a height of 1.8 m and then onto a horizontal surface where it has a head-on elastic collision with a stationary 2.0 kg cart cushioned by an ideal Hooke’s law spring. The maximum compression of the spring during the collision is 2.0 cm...
  16. J

    Speed of an antimuon in a pi meson decay

    Homework Statement I'm trying to confirm the speed of an antimuon in the \pi^+ \rightarrow \mu^+ \nu_{\mu} decay through the laws of conservation but it doesn't add up. Homework Equations [/B] 1.Energy-momentum relation: E^2 = (pc)^2 + (mc^2)^2 2. Rest masses: m_{\pi} = 139.6 \...
  17. H

    Relation between energy conservation and numerical stability

    Hi, Consider the conservation laws for an isothermal linear incompressible flow governed by the mass and momentum equation. The kinetic energy equation is then solved to see if energy conserved. Can anyone tell me if once it is shown energy is conserved, it implies that convergence is obtained...
  18. F

    What determines if a reaction is exotermic or endotermic?

    Using a more physics oriented approach, rather than a chemistry one, and looking to an energy point of view if possible. For example, why when ice turns into water there is a need for energy (heat)? I know in some extent that the energy is used into re-organizing the chemical bonds, but that...
  19. F

    Potential Energy and Conservation of Energy

    Homework Statement A 700g block is released from rest at height Ho(initial) above a vertical spring with spring constant k=400 N/m and negligible mass. The block sticks to the spring and momentarily stops after compressing the spring 19.0 cm. How much work is done A) by the block on the spring...
  20. M

    Is energy conserved in an object sliding down an inclined plane on ice?

    1. A ball falls to the ground through the air. Is the energy of the air conserved?2. None3. When a ball falls to the ground a transformation of energy occurs. The previously stored potential energy gradually becomes kinetic energy during its fall. The energy conserved in the air is the slight...
  21. D

    Conservation of Energy for the Universe

    The conservation of the energy of the universe requires that the universe is an isolated system. Is there any way that, in fact, the universe isn't a isolated system and we would be losing or gaining energy in the universe? Also, does this possibly mean that the universe won't necessarily end in...
  22. S

    Coffee + Sugar = Extra Calories?

    I am a big physics enthusiast, and I apply my learning as much as possible. Today, my literature teacher introduced this idea that when coffee and sugar are combined, new calories are born. For instance, coffee (0 kcal) + sugar (100 kcal) = 150 kcal? Unfortunately, I only pursued physics and...
  23. I

    Law of conservation of energy

    Does the law of conservation of energy make valid predictions when energy is converted from gravitational potential energy into kinetic energy?
  24. S

    Finding final velocity for Conservation of Energy Problem

    Homework Statement Problem statement and diagram in the photo Homework Equations K = 1/2 mv^2 U = mgh The Attempt at a Solution E_0 = E1 K_0 + U_0 = K_1 + U_1 using relevant equations and solving for v1 I get: v_1 = sqrt((v_0)^2 + 2gh_1) Then E_1 = E_2 solving for the final velocity and...
  25. N

    Spring Compression (x-x0) = .00579 m

    Homework Statement A spring (k = 2900 N/m ) is compressed between two blocks: block 1 of inertia 1.70 kg and block 2 of inertia 2.00 kg. The combination is held together by a string (not shown in (Figure 1) ). The combination slides without spinning across low-friction ice at 2.90 m/s when...
  26. D

    Conservation of energy violation of galvanic cell electron

    When a galvanic reaction reclaims its (single) electron, magnetic energy (about 0.356 eV) within a superconductor will remain, w/o a means of replacing the galvanic electron. During the reaction, electrical current from the single electron would correspond to the number of times per second...
  27. S

    What Is the Total Work Done on a Cyclist Ascending an Incline?

    Homework Statement A man on his bike have an initial velocity of 8.5m/s. He begins to go up an incline that has a vertical height of 5.2m. Once he reaches the top of the incline, he only has a velocity of 3.00m/s. The man and his bike combined weigh 80kg. What is the total work done on the...
  28. bigsmile

    Positive and negative signs on Work

    Homework Statement An amount of work equal to 1.5 J is required to compress the spring in a spring gun. ? Homework Equations Wtotal = change of KE[/B] The Attempt at a Solution W=ΔKE=(1/2)m(Vf² - Vi²) It sounds like the Vf >0 and would be maximum after the spring is compressed hard and...
  29. bigsmile

    Why Does Dropping a Ball into a Well Result in Different Energy Sums?

    A 2.00-kg ball has zero kinetic and potential energy. John drops the ball into a 10.0-m-deep well. 1) Just before the ball hits the bottom, the sum of its kinetic and potential energy is: Zero J 2) After the ball comes to a stop in the mud, the sum of its potential and kinetic energy is: -196...
  30. bigsmile

    Pendulum - Maximum Angle in 2nd half of swing

    A simple pendulum, 2.0 m in length, is released by a push when the support string is at an angle of 25° from the vertical. If the initial speed of the suspended mass is 1.2 m/s when at the release point, to what maximum angle will it move in the second half of its swing? Let h1 be the...
  31. asdfg

    Conservation of energy, bungee jumping

    Homework Statement A daring friend of yours talks you into bungee jumping from the Royal Gorge Bridge, in Colorado. Starting from the bridge (at rest), you launch off and fall first to the unstretched length of the bungee, 153 m. The bungee then stretches until you reach the full drop distance...
  32. halpmaine

    Conservation of Energy -- does it ever not apply?

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

    Conservation of Energy and Non-Conservative Forces

    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)...
  34. N

    Conservation of Energy and Momentum

    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?
  35. H

    B The Problem That Riddles Any Radical Thinker: WTH Is Energy

    Hello! I'm new to this forum but ok let's get this started, First I'll revisit the definition I know as physics; the study of nature in order to provide a reasonable(radical/rudimentary) explanation/reason. This I believe in is not quite how things are today, at school, with my teachers or at...
  36. B

    Applying Conservation of Momentum along the Y axis

    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...
  37. ElegantSir

    Law of Conservation of Energy of a wind turbine

    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...
  38. Chrono G. Xay

    Calculate the 'Feel' of a Drumhead?

    As another of my personal music projects, I have wondered if it would not be possible to calculate the 'feel' of a drumhead (i.e. the amount of 'give' expressed as transverse displacement 'z' that an equally pre-tensioned circular membrane of radius 'r' experiences when struck on its plane at a...
  39. gonadas91

    Energy Conservation in Quantum Systems - Is it Possible?

    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!
  40. O

    Task: Function for the acceleration throughout a loop?

    So, this seemed really fun to me until I got stuck. THE TASK is about an object with mass m, moving in a basic (2D) coordinate system. It is attached to origo (0, 0) by a "rope" with constant length r=5. In position P0(-5, 0) it has the velocity v0=[0, -10]. Hence, the object moves around origo...
  41. B

    Understanding why change in Kinetic Energy is 0

    Homework Statement Find the minimum force ##\displaystyle F## required to move ##\displaystyle M_2##.Details and Assumptions: ##\displaystyle M_1 = 3Kg## ##\displaystyle M_2 = 5Kg## ##\displaystyle \mu_1 = 0.4## ##\displaystyle \mu_2 = 0.6## ##\displaystyle g = 9.8m/s^2## Homework...
  42. G

    Law of the lever: Conservation of energy or angular momentum

    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...
  43. C

    Identical Hollow and Solid Spheres

    Homework Statement Two spheres look identical and have the same mass. However, one is hollow and the other is solid. Describe an experiment to determine which is which. Homework Equations mgh= ½ m v^2 + ½ I ω^2 where I= 2/3 mr2 for a hollow sphere I=2/5 mr2 for a solid sphere The Attempt...
  44. B

    Rope hanging from a table, find time taken to fall off table

    Homework Statement A rope of uniform mass per unit length ##\lambda## and length ##L## lies curled on a table, with a short length ##\delta l## of it hanging through a hole in the table. At time zero, the rope begins to slide through the hole. At what time ##t_c## (in seconds) does the end of...
  45. B

    2 sphere system, Conservation of Energy and Momentum

    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...
  46. A

    Conservation of energy for a system

    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...
  47. A

    Conservation of energy word problem

    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...
  48. A

    How do I find final velocity using conservation of energy

    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...
  49. montrex

    Impulse applied to an elastic pendulum

    Homework Statement A pointlike body of mass ##m=100## ##g## is attached to the extremity of an ideal spring, whose constant is ##K## and its length at relaxed position is negligible. The other extremity of the spring is attached to the fixed point ##O##. At first the body mass, on which the...
  50. N

    Work applied to a spring by my finger muscles

    I take a spring and expend work to compress it with my fingers thereby increasing the potential energy of the spring. After it is at its final compressed state, am I doing work?
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