What is Kinetic: Definition and 1000 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










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. B

    Average kinetic energy/ temperature confusion

    My mcat book says temperature is a measure of the total kinetic energy of a system. Then later on it says temperature is a measurement of the average kinetic energy of a system. Is this an error? Thank you.
  2. C

    Finding coefficient of kinetic friction

    Homework Statement A 100 N force directed 37° below the horizontal is applied to a 30 kg object on a horizontal surface. If the magnitude of the acceleration of the object is 1.3 m/s2, what is the coefficient of kinetic friction (μk) between the object and the surface? Homework Equations...
  3. Salvador

    Electron kinetic energy, movement

    I read that based on temperature , electrons have kinetic energy in metals so they randomly move around the ion lattice. when we apply current to a room temperature conductor, the electrons being charge carriers align and form current? but what happens in the plates of a capacitor , when the...
  4. M

    An expression about kinetic energy

    Hi, all. Here is an expression about kinetic energy from analytical dynamics of Haim Baruh which confuses me. "Consider a particle and the case which the kinetic energy is only quadratic in terms of velocity of the particle. We take the differential form of work-energy principle and remove...
  5. PsychonautQQ

    Kinetic Energy of particle in 1D and 3D well

    So my professor said that the Kinetic energy of the particle in a 3D infinite well is dependent on position where in a 1D infinite well it's NOT dependent on position. She is sort of notorious for being wrong apparently and many of my undergrads are telling me she is wrong. I understand that...
  6. T

    What is the kinetic energy of electron at room temperature?

    is it related to fermi energy? what is the exact equation form?
  7. T

    BBKGY equations of kinetic theory

    Are there any good books to understand the BBKGY equations of kinetic theory?
  8. Q

    Kinetic energy relative or absolute?

    Hello folks! I have just come from a night at the pub with fellow students of life where over many a pint several mysteries of the universe were discussed. One of my friends asked me a question concerning special relativity that initially took me by surprise and which has me wondering about the...
  9. BitWiz

    Is interstellar travel impossible due to kinetic energy magnitude?

    This has been bugging me. Several respected propulsion scientists at the 2008 Joint Propulsion Conference claimed that interstellar travel within a human lifetime was impossible. The KE of a rocket traveling at a significant fraction of c would be enormous via KE=0.5 * m * v^2 and that...
  10. C

    Kinetic Moment about the center of gravity

    Hi I need some help explaining kinetic moment and moment of the center of mass. This is an example: http://session.masteringengineering.com/problemAsset/1529176/3/Hibbler.ch17.p107.jpg Okay I know that when you do moment equations: The Moment forces about some point is = to the kinetic...
  11. N

    Standard Deviation of Kinetic Motion

    If thermodynamic temperature can be interpreted as the average kinetic energy in a system, is there a quantity defined as the standard deviation? For example, let's say you poured some hot water into a cup of cold water. The instant you poured it the standard deviation of the system would be...
  12. S

    Kinetic Energy of Rotating Solid disk or cylinder about symmetry axis

    Homework Statement A horizontal 845.0 N merry-go-round with a radius of 4.3 m is started from rest by a constant horizontal force of 74.0 N applied tangentially to the merry-go-round. Find the kinetic energy of the merry-go-round after 2.2 s. Assume it is a solid cylinder. The...
  13. T

    Maximum radius given rps, static and kinetic friction coefficients

    Homework Statement A computer scientist has dropped a tiny pizza crumb onto a magnetic disk. Later, when it's turned on, the disk is rotating at 88 revolutions per second about its axis, which is vertical. The coefficients of kinetic and static friction between pizza crumbs and the disk are...
  14. J

    Calculate the change in the loader’s kinetic energy

    Linear Momentum question - help please Homework Statement A 15,000 kg loader traveling east at 20 km/h turns south and travels at 25 km/h. Calculate the change in the loader’s kinetic energy. linear momentum. Homework Equations KE2-KE1 = change in KE p=mv The Attempt at a Solution a...
  15. jdawg

    Kinetic energy dissipated during inelastic collsion

    Homework Statement Blocks A and B are moving toward each other. Block A has a mass of 2.0 kg and a velocity of 50 m/s, while B has a mass of 4.0 kg and a velocity of -25 m/s. They suffer a completely inelastic collision. The kinetic energy dissipated during the collision is: Homework...
  16. O

    Find relativistic momentum of electron given kinetic energy.

    Homework Statement At what energy does an electron become “relativistic”? Consider electrons with kinetic energies of 50 eV, 50 keV, and 50 MeV. For each case, calculate the momentum of the electron first using the non-relativistic formula for kinetic energy, and then using the correct...
  17. P

    Harnessing kinetic energy from impact of rain water

    I read in a science magazine that you would be able to generate more energy by collecting a mass of water and tipping it through a turbine than from generating energy from the impact of that mass of water as individual raindrops. Now this may simply be to do with the technology we have that...
  18. U

    When Does the Kinetic Work Energy Theorem Not Apply?

    When does the Kinetic Work Energy Theorem not apply to a situation? Or better, is there a general form of the equation where work can equal the change in any energy? What is work besides a force and a distance?
  19. R

    How much work is done on the ice block?

    Homework Statement An ice block is being pushed through a displacement d→=(15m)i -(12m)j along an embankment with rushing water. It exerts F→=(210N)i -(150N)J on block. How much work on block does force do? Homework Equations W=Fxd Pythogoreum equation a^2 +b^2= c^2 The Attempt...
  20. jdawg

    Momentum and kinetic energy in collisions with a bullet

    Homework Statement A bullet of mass 4.2 g strikes a ballistic pendulum of mass 2.0 kg. The center of mass of the pendulum rises a vertical distance of 18 cm. Assuming that the bullet remains embedded in the pendulum, calculate the bullet's initial speed. Homework Equations The...
  21. P

    First passage time for Kinetic Monte Carlo model

    Hi all! I have a problem on finding the first passage time for kinetic monte carlo model. Suppose I have a linear kinetic model for n states: S1<->S2<->S3<->...<->Sn where all the rate constants k_ij for transition between any two states are known. Is there any general way to find out the...
  22. C

    How to Write Mathematical Equations on Physics Forums

    Homework Statement If the velocity of a rocket is 10 meters per second and its mass is 10 kg, its kinetic energy is: a. 5000 joules b. 500 joules c. 10000 joules d. 1000 joules [b]2. Homework Equations [/b) Ek= (1/2) mv2 The Attempt at a Solution e=(.5)10x10(2) E=5000 j
  23. C

    Different types of energy: kinetic vs potential vs

    1. Homework Statement What type of energy does a blackboard eraser have when I hold it steady three feet about the ground? a. potential energy b. kinetic energy c. electrical energy d. spring elastic energy I think it is kinetic energy. But I am confused on the differences of...
  24. R

    Bar suspended by rope kinetic energy

    If I needed to calculate the kinetic energy of a bar suspended by a rope at one of its ends, in other words, a bar pendulum, do I need to calculate the kinetic energy of the center of mass plus the kinetic energy relatively to the center of mass or do I need to calculate the kinetic energy of...
  25. M

    Coefficient of Kinetic Friction

    "A hockey puck is hit on a frozen lake and starts moving with a speed of 12 m/s. Exactly 5.0 s later, its speed is 6.0 m/s. What's the puck's average acceleration? What is the coefficient of kinetic friction between the puck and the ice?" I've calculated the acceleration, but I'm stuck when it...
  26. P

    How Much Work Is Required to Move a Refrigerator Across a Frictional Surface?

    Homework Statement A 100 kg refrigerator is on rest on the floor.How much work is needed to move the refrigerator at a constant speed for 6 m along with a floor friction force of 200 N ? Homework Equations I used ΔK = W(Fg)+ W (N) + W(f)+ W(T) =0 and W(Fg)+ W (N) = 0 so W(T)=-W(f)=f*...
  27. L

    Potential and Kinetic Energy on a swing as well as Tension in the rope

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  28. D

    Calculating Final Velocity with Given Work and Mass

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  29. M

    Solving the Angular Momentum & Kinetic Energy Equations: Find ωa & ωb

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  30. F

    Photoelectric Effect: Working out kinetic energy of photoelectron

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  31. M

    Formulas converting Potential Energy to Kinetic Energy

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  32. P

    Rate constant and Kinetic model

    Hi everyone, I have a question on the rate constant of a kinetic model(like the one we use in describing chemical reaction). Suppose we have the following model between two states A and B: A--(a)-->B A<--(b)--B where a, b are the rate constant for the transition. So the corresponding...
  33. B

    Can we calculate kinetic energy by multiplying 1/2mv^2 by 1.15 at C/2 speed?

    If an electron is traveling at C/2, the Lorenz formula says that mass is about 1.15 me, do we get the value of KE simply multiplying 1/2mv2 by 1.15? Is it as simple as that?
  34. J

    Kinetic energy of rocket explosion

    Homework Statement a rocket explodes in flight into two equal mass pieces still going in the same direction with one piece moving twice as fast as the other. What is the ratio of the total kinetic energy of the pieces just after the explosion to that of the rocket just before? Homework...
  35. S

    Derivative Method for Error in Kinetic Energy formula

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  36. A

    Acceleration of a block with static & kinetic friction

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  37. G

    Change in Kinetic Energy for a Sliding Box

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  38. S

    What is the Relationship Between Solar Wind and Kinetic Energy?

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  39. B

    How Do You Calculate the Coefficient of Friction for a Slowing Truck?

    A 4700 kg truck carrying a 900 kg crate is traveling at 25 m/s to the right along a straight, level road, as shown below. Suppose the brakes are applied for 3.0s. During this 3.0s the truck travels 55 m. 1. Calculate the acceleration of the truck during the 3.0s interval. (Assume it is...
  40. M

    Finding Kinetic Energy from graph of Power

    Homework Statement Homework Equations P = dW/dt Change in work = Change in Kinetic Energy The Attempt at a Solution Since the integral of the power graph is work done in the system, and since it starts at 0, does this mean kinetic energy is the same thing? So I can probably make...
  41. T

    Query about kinetic energy equation e = ½mv^2

    Hi I don't understand why the relationship between kinetic energy and velocity is not linear. Consider the following situation: 1. A rocket is traveling through space at constant velocity with it's thrusters switched off. 2. The thrusters are fired at full blast for precisely one second...
  42. M

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    Homework Statement Question in entirety: Vladimir Putin has contacted you to redesign the ski jump at the Olympic games. In the ski jump, contestants begin at rest at the starting gate on top of a hill inclined at an angle of 30 with respect to horizontal. They then accelerate down the hill...
  43. M

    Average kinetic energy of a damped oscillator

    For a damped mechanical oscillator, the energy of the system is given by $$E = \frac{1}{2}m \dot{x}^2 + \frac{1}{2}k x^2$$ where ##k## is the spring constant. From there, I've seen it dictated that the average kinetic energy ##\langle T \rangle ## is half of the total energy of the system. This...
  44. M

    Change in a rocket's kinetic energy

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  45. D

    Kinetic energy of a free electron in a lattice

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  46. C

    How do collisions between gas molecules result in equal average kinetic energy?

    Hi, I was wondering, how is it possible that different gases can have the same average kinetic energy?(at same temperature) Can anybody give me a SIMPLE explanation of this? Knowing that some particles will move faster than others, I wonder how this can be possible :/ It would really help ...
  47. C

    Comparing Kinetic Energy of N2 and CO2 Molecules at Ambient Conditions

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  48. Q

    Questions about kinetic energy and momentum

    Hi, I am currently in High School physics and we are going over Energy and Momentum. I have some questions about how and why they both work. *all objects are assumed to have the same mass Since [Kinetic Energy=1/2mv^2], an objects Kinetic energy is proportional to the square of its...
  49. PsychonautQQ

    Calculating the Kinetic Energy of an Electron in X-Ray Radiation

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