Kinetic energy Definition and 1000 Threads

In physics, the kinetic energy of an object is the energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest.
In classical mechanics, the kinetic energy of a non-rotating object of mass m traveling at a speed v is










1
2


m

v

2









{\displaystyle {\begin{smallmatrix}{\frac {1}{2}}mv^{2}\end{smallmatrix}}}
. In relativistic mechanics, this is a good approximation only when v is much less than the speed of light.
The standard unit of kinetic energy is the joule, while the English unit of kinetic energy is the foot-pound.

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  1. S

    Average kinetic energy of particles of an ideal gas

    Homework Statement So first the task: Determine the average value of the kinetic energy of the particles of an ideal gas at 0.0 C and at 100 C (b) What is the kinetic energy per mole of an Ideal gas at these temperatures. I took the above right out of the pdf we got from our professor. I know...
  2. physicsisgreat

    Decelerating box on a truck and work

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  3. D

    Equation used to find kinetic energy of proton

    I am having trouble deciding when to use which equation. If you're given the wavelength of a proton, let's say 100 fm, and have to find the kinetic energy of it, how would you do this? Here are my ideas: Idea 1: Use lambda = h/p, where p = sqrt(2Em). Idea 2: Use E=(pc)^2+(mc^2)^2 =...
  4. goonking

    Kinetic energy to thermal energy

    Homework Statement Homework Equations Q = c m ΔT The Attempt at a Solution so converting 55 mph to meters per sec gives me a velocity of 24.58 m/s kinetic energy of car is 1/2 m v2 i set 1/2 m v2 = c m ΔT plugging in v and c and masses of both ΔT = 134.56 is that correct?
  5. moenste

    Speed of bullet and kinetic energy lost in the impact

    Homework Statement A bullet of mass 2.0 * 10-3 kg is fired horizontally into a free-standing block of wood of mass 4.98 * 10-1 kg, which it knocks forward with an initial speed of 1.2 m s-1. (a) Estimate the speed of the bullet. (b) How much kinetic energy is lost in the impact? (c) What...
  6. T

    How to use kinetic energy for this problem?

    Homework Statement The problem is that my teacher asked to solve this using kinetic energy but i doubt it uses kinetic energy... i thought it uses potential energy. [/B] You put your little sister (mass m) on a swing whose chains have length L and pull slowly back until the swing makes an...
  7. R

    What is the Kinetic Energy of an Alpha Particle from 210Po Decay?

    Homework Statement The kinetic energy (in keV) of the alpha particle, when the nucleus 84210Po at rest undergoes alpha decay, is A 5319 B 5422 C 5707 D 5818 Homework Equations ## E = mc^2 ## Kinetic energy ## = mv^2/2 ## The Attempt at a Solution alpha particle is emission of helium nucleus...
  8. Glenboro

    How Does Kinetic Energy Change in a Baseball After Being Hit?

    Homework Statement After being hit, a 0.145 kg baseball has a speed of 45.6 m/s. 1. What is the kinetic energy of the baseball after it has been hit? 2. How much work is done on the baseball by the baseball bat? 3. In moving through the air, the baseball slows down to a speed of 30.0 m/s...
  9. W

    Electric potential, Can Someone Check This?

    Homework Statement A particle charge of 7.6μC is in a uniform electric field directred to the left. Another force, in addition to the electric force, acts on the particle so that when it is released from rest it moves to the right. After it has moved 8cm, the additional force has done...
  10. Sampad Saha

    How does Potential Energy converted into Kinetic Energy? ?

    As we know that every object that has kinetic energy could also have potential energy. Now suppose an object is in rest at a distance of h meter from ground so it has some potential energy and no kinetic energy, now if it starts to fall towards the ground can we say that its total potential...
  11. Buzz Bloom

    How does a particle's kinetic energy vary with a(t)?

    I am curious about how a particle's kinetic energy changes with the explansion of the unverse. I calculated that for a matter dominated universe it would vary as 1/a2, while the photon temperature varies as 1/a. Is this correct? Is this also true in general? If so, the implication would be...
  12. L

    Average values of operators of potential and kinetic energy

    In case of quantum LHO in eigen state of the system ##|n \rangle## \langle \hat{T} \rangle=\langle \hat{U} \rangle=\frac{1}{2}(n+\frac{1}{2})\hbar \omega What will happened in some superposition of states? Does Ehrenfest theorem can tell me something more general? Is it possible to say that...
  13. shanepitts

    Average kinetic energy of harmonic oscillator

    I was wondering why the average kinetic energy is calculated in this manner. They are dividing the kinetic energy function by the period (noted here as To) and integrating it with limits from 0→To. Why? (This is a tiny portion of a larger textbook example, not an actual assignment.) Sorry for...
  14. Mr Davis 97

    Does v represent speed in kinetic energy formula?

    Since kinetic energy is in is a scalar quantity in joules, then is the v in (1/2)mv2 speed or velocity?
  15. Y

    How to calculte Kinetic Energy of Scissor Lift system

    Hi, here i need to calculate the tilt angle of the scissor lift. I had done some reviews for designing a scissor lifter, some source state that, tip-over will happen only when the kinetic energy of the system is less than the Potential energy after impact. Hence, i was trying to use this...
  16. Mr Davis 97

    Data for a potential and kinetic energy experiment

    I have performed an experiment testing how mechanical energy is conserved. I conducted this experiment by first creating a ramp. I gathered data by first calculating the gravitational potential energy of a marble on various points on the ramp (depending on height). Next I rolled the ball down...
  17. A

    Relativistic Kinetic Energy as a solution to a DE

    Has anyone ever seen KE derived this way? The only non-classical assumption is that mass = Energy/c^2 (I know, that's a big one) and that it accumulates as mass as the object is accelerated. (sorry for the plain text formatting, I need to learn how to do it right, I may reply with my first try)...
  18. J

    Temperature and Average kinetic energy of moleces

    1. The temperature of air wil ... if we add a hydrogen molecule of a speed higher than 1980 m s/-1. 2. The temperature of air will ... if we take away a hydrogen molecule of a speed highr than 1980 m s /-1. 3. The temperature of air will ... if we take away a hydrogen molecule of a speed lower...
  19. aladinlamp

    Kinetic Energy vs Momentum vs Power

    Imagine this object as a big tanker ship, moving to the right weight 500 000 metric tones linear velocity 0.01 m/s momentum cca 5 000 000 kg m/s kinetic energy 25 000 J, which is 25 kilowatt-secondshow much power could i extract from this object in order to slow it down to complete stop ...
  20. Quarlep

    Does a Moving Sphere's Kinetic Energy Affect Its Atomic Particles?

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  21. P

    Can a Flywheel Store 1 MW of Power for 50 Seconds with Only 33% Energy Loss?

    Hi fellow scientists and engineers, I have a question regarding the design of a flywheel. I know that the actual engineering of a flywheel is very complex and in no way I should expect actual practical answers from this simple question. I'm just trying to get some estimates for a renewable...
  22. B

    Comparing force of mass at rest vs falling mass

    What equations can be used to compare the force of a resting X mass to the force of a smaller Y mass falling Z distance. Specifically, how much resting mass would equal the force of 300 pounds being dropped from 10 feet up?
  23. L

    Kinetic energy of Earth and ball system

    Homework Statement There is a system consists of a ball and the earth. Explain why you can consider the kinetic energy of the system equals to the kinetic energy of the ball. Homework Equations ##F=-\frac{m_{1}m_{2}}{{r}^{2}}## The Attempt at a Solution The magnitude of the force acting on...
  24. manogyana25

    Average kinetic energy of the molecules in a cold liquid less?

    Why is the average kinetic energy of the molecules a cold liquid less? As the temperature of a liquid decreases, the average kinetic energy of its molecules reduce. What is the reason behind this?
  25. F

    Do you consider both regular and rotational kinetic energy?

    Homework Statement If I have a ball moving in a circular path (ball is connected to a string), as shown in this picture: http://w3.shorecrest.org/~Lisa_Peck/Physics/syllabus/mechanics/circularmotion/Images/cent_force_on_ball.gif should I say that the energy of the ball is both its kinetic...
  26. E

    Work, Force, Energy and power question about moving car.

    Homework Statement A car has a power output of 45kW and travels at a constant speed of 30m/s. What force is the engine applying on the car? Homework Equations F=m*a W=ΔKE+ΔGPE KE=½mv^2 GPE=mgh W=F*d P=ΔE/ΔT gh_1+½v_1^2=gh_2+½v_2^2 The Attempt at a Solution I really have no clue. Since there...
  27. R

    Speed parameter β and Lorentz factor γ

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  28. Helmet

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  29. K

    Spring pendulum, Kinetic Energy

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  30. CAH

    Electrons absorb exact energy photons so how is Ek possible

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  31. P

    Obtaining kinetic energy equation.

    The question is about 2 sticks standing above each other, but i have a more general question. The position of my mass is described by: (2rsin(a) - rsin(b) , 2rcos(a)+rcos(b)) the goal is to get a formula for the kinetic energy, so i need the speed of the mass. If i take the derivatives of...
  32. Chrono G. Xay

    Kinetic Energy of Double Compound Pendulum and Parallel Axis

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  33. Dadface

    Is 'Carrying' the Right Term for Describing Kinetic Energy in Moving Objects?

    I think its correct to state that: "Kinetic energy is a property of a moving object." But would it be correct to state that: "Kinetic energy is carried by a moving object"? If not is there a better alternative terminology to use? Thank you.
  34. xxyourstruly

    How do I calculate percent elasticity?

    Homework Statement I was given a chart to figure out the different momentum and kinetic energies of different collisions (elastic and inelastic) and in the lab he posed the question "Calculate the percent elasticity for each of the collisions." Homework Equations conservation of momentum...
  35. T

    I have one question regarding Kinetic Energy

    The question is. There are two particles, one with charge -q and the other with charge Q, and -q particle rotates around the Q particle at a radius r1. What is the Energy at this point? The answer is like this: E= KE + U So now I know that U= -kQq/r1 But according to the answer: KE= kQq/2r1...
  36. G

    How much kinetic energy is released

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  37. Phynos

    Relativistic kinetic energy - particle decay

    Homework Statement A pion at rest (mπ = 273me) decays into a muon (mμ = 207me) and an antineutrino (mn ≈ 0). Find (a) the kinetic energy of the muon and (b) the energy of the antineutrino in electron volts. Homework Equations K = (γ-1)mc2 E = γmc2 ER = mc2 E2 = p2c2 + (mc2)2 I didn't...
  38. G

    Energy question about kinetic energy and potential

    Homework Statement [/B] Objects A and B, of mass M and 2M respectively, are each pushed a distance d straight up an inclined plane by a force F parallel to the plane. The coefficient of kinetic friction between each mass and the plane has the same value...
  39. 1

    Conservation of Angular Momentum & Energy question

    Question: A streetcar is freely coasting (no friction) around a large circular track. It is then switched to a small circular track. When coasting on the smaller circle its speed is: a) greater b) less c) unchanged Relevant Formulas: w = v/r KE = 1/2mv2 My teacher said the normal force from...
  40. B

    Kinetic energy of object free fall

    If an object is dropped from height, h, then gravitational energy is E = mgh, but kinetic energy when object hits the ground is E=(1/2)mv^2. Conservation of energy states that E(g)=E(k). Why does kinetic energy not depend on height object was dropped?
  41. goonking

    Solving for Height of a Falling Cube Using Kinetic Energy

    Homework Statement Homework Equations 1/2 mv^2 = mgh The Attempt at a Solution first, a side question, if p = mv, can't we just place p into 1/2 mv^2 so it becomes 1/2 p^2? anyway, on to the question, at the point where the cube falls off, the Fnormal should just about equal 0, correct? is...
  42. C

    Prove Kinetic Energy equation (without calculus)

    Homework Statement Prove kinetic energy is relationship between mass and velocity using E(g)=mgh (no calculus, momentum, kinematics). Homework Equations gravitational energy: E=mgh kinetic energy: E=(1/2)mv^2 The Attempt at a Solution I know it can be derived using the gravitational energy...
  43. B

    Box on Inclined Plane (with Friction)

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  44. C

    Kinetic Energy Time Derivative

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  45. davidbenari

    Does kinetic energy increase the inertial mass?

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  46. M

    Bungee jump height/spring energy

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  47. N

    Does electromagnetic radiation actually carry kinetic energy?

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  48. K

    I with rotational kinetic energy problems

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  49. T

    Work, Kinetic Energy, Spring, Friction Problem

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  50. H

    A spring and two blocks with kinetic energy

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