Kinetic energy Definition and 264 Discussions

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





{\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. A

    Work, Gravitational Potential and Kinetic Energy, Spacecraft

    Hi guys. I'm new to this forum so I'm not sure if I'm posting this in the right place or correctly, but I was totally stumped on a Physics 12 question as I was studying for my exam. The question is: An explorer spacecraft is descending towards Mars using a rocket engine for braking. The...
  2. G

    Stuck on projectile motion problem using gravitational force

    Homework Statement A projectile is fired vertically from the Earth's surface with an initial speed of 11.4 km/s. Neglecting air drag, how far (in meters) above the surface of the Earth will it go? Homework Equations (1/2)mv^2 -GmM/R The Attempt at a Solution KEi+PEi = KEf+PEf (1/2)mv^2 -...
  3. L

    Relate rotational kinetic energy to potential energy

    Homework Statement This problem is from the 2015 AP Physics C Mechanics free response, question 3 part b. Homework Equations K = 1/2Iω2 U = mgh The Attempt at a Solution The potential energy of the bar when...
  4. R

    A Electron's kinetic energy

    Hello to All ! I have a question that Whenever an electron from bulk material trapped by a quantum well that electron's 3rd dimensional kinetic energy component vanishes, But where that goes, is it added to the other 2 dimensional kinetic energy components..?
  5. H

    Collisions -- conceptual questions

    Homework Statement Let two particles of equal mass m collide. Particle 1 has initial velocity v, directed to the right, and particle 2 is initially stationary. A: If the collision is elastic, what are the final velocities v_1 and v_2 of particles 1 and 2? B: Now assume that the mass of...
  6. A

    What fraction of its energy does accelerating proton shed?

    Homework Statement If a proton with a kinetic energy of 6 MeV is traveling in a particle accelerator in a circular orbit of radius 0.75m, what fraction of its energy does it radiate per second? m = 1.67 * 10^-27 epsilon_0 = 8.854 * 10^-12 c = 3 * 10^8 Homework Equations dE/dt = (q^2 a^2) /...
  7. Jared

    Need help finding energy for escape velocity

    Homework Statement The gravitational potential energy of a certain rocket at the surface of the Earth is -1.9x10^12 J. The gravitational potential energy of the same rocket 300km above the Earth's surface is -1.8x10^12 J. Assume the mass of the rocket is constant for this problem. A) How much...
  8. Metovich

    Question About Potential Energy

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  9. P

    Explosion and conservation of momentum problem

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  10. StillLearningToronto

    HW Help: Mass and Kinetic Energy

    Question: Calculate the kinetic energy required to accelerate a single proton from rest position to 0.9999c. The mass of the proton is 1.67*10^-27 kg. Equations Used: Ek=(mc^2/√ 1-(v^2/c^2))-mc^2 Attempt at the problem: Ek=(1.67*10^-27kg)(3*10^8m/s)^2/√...
  11. Z

    Kinetic energy and momentum

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  12. RavenBlackwolf

    Conservation of Energy, Down an Incline with a Spring

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  13. xjcov

    Analysis of collisions from data

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  14. J

    1/2 m v^2 in a circle?

    Homework Statement in circular motion (e.g. a pendulum) is the kinetic energy still 1/2 m v ^2 or is it a different equation? Homework Equations 1/2 m v ^2 The Attempt at a Solution
  15. M

    Work done on brakes vs kinetic energy lost by vehicle

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  16. V

    Should I consider Linear Kinetic Energy in this Equation

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  17. fuvest

    Mechanical Energy Problem/non-conservative forces

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  18. I

    Efficiency question

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  19. C

    Ball doing a loop

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  20. Ian Baughman

    Electron in orbit of around a single proton

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  21. J

    I Energy transfer during uphill vs downhill running

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  22. cheapstrike

    Impulse and kinetic energy?

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  23. F

    How much kinetic energy do I need to impart?

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  24. M

    A spring with a force constant

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  25. A

    Car Crash Work and Energy Problem

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  26. H

    Kinetic energy change with initial velocity

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  27. C

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  28. Cocoleia

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  29. adjacent

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  30. K

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  31. moenste

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  32. Wout Veltman

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  33. moenste

    V required so ions passing through the region don't devitate

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  34. energeticringleader

    Rest, Mass, and Kinetic Energy

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  35. Oannes

    Finding Horsepower given Pressure, Diameter, and Distance

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  36. M

    Center of momentum frame question:

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  37. Oannes

    Finding the Value of Gravity Given Height and Velocity

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  38. O

    Potential difference of helium nucleus question

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  39. S

    Velocity & Kinetic Energy

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  40. N

    Water wheels and mathematical equation

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  41. X

    Inelastic Collision

    In an inelastic collision is the change in kinetic energy equal to the difference of final and initial momentum if one of the objects is initially at rest? For example: m1v = (m1+m2)Vf -----> 0 = (m1+m2)Vf - m1v1 1/2(m1+m2)Vf^2 - 1/2m1v^2 = (m1+m2)Vf - m1v1 Or totally wrong? Thanks!
  42. UMath1

    Momentum conservation inelastic collection

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  43. S

    Solve questions on oscillations and kinetic energy

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  44. O

    Finding displacement using net work?

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  45. JayaSuria

    Inelastic Collision - Kinetic Energy

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  46. A

    Finding relativistic mass and energy of an electron

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  47. J

    Calculate height and velocity given kinetic and potential?

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  48. bebop1

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  49. bebop1

    Kinetic Energy and Collision Question

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  50. B

    Kinetic Energy from a Simple Harmonic motion and spring

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