What is Kinetic energy: 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.

View More On Wikipedia.org
  1. J

    Rotational Kinetic Energy of Body in another body reference frame

    I have two rigid bodies floating in space that are kinematically constrained by a joint (think of a 2 dof link mechanism floating in space). I have a body fixed reference frame on each rigid body plus the global space-fixed reference frame. The first rigid body is in the space-fixed...
  2. C

    Relative momentum, Rest Energy, Kinetic energy and speed of a proton

    1. a) A relativistic proton has a momentum of 10x10^-18 kg*m/s. The rest energy of a proton is 0.150nJ. The kinetic energy of the protoon b) In this situation the speed of the proton is? 2. E=MC^2 P= MV/sqroot(1-(v^2/c^2) K=[MC^2/ sqroot(1-v^2/c^2)]-[mc^2] 3. The algebra in this problem...
  3. S

    Kinetic Energy after a Collision

    Homework Statement A 110 kg football player runs at 2.75 m/s directly into a 125 kg player running 2.60 m/s towards him. What is the kinetic energy of the two players if this is a completely inelastic collision. Homework Equations P = m*v Ptotal = Pi - Pf K = 0.5*m*v^2 The...
  4. shounakbhatta

    Average kinetic energy of molecules

    Hello, The formula for average kinetic energy of molecule is: k=3/2KT. Can anyone please explain the derivation without using calculus? Thanks, -- Shounak
  5. K

    Find the kinetic energy of the alpha particle

    Homework Statement For the decay " Uranium-232 ---> Thorium-228 + alpha particle ", What is the alpha particle's kinetic energy in the U-232 atom's rest frame? We are given the masses for each one. Homework Equations E = mc^2 The Attempt at a Solution I tried mass(U-232) -...
  6. R

    Kinetic energy to heat problem

    Homework Statement 1.5ton (1500kg) object is dropped from 20 meters into a bucket with 2.5L of water in it. All the kinetic energy is transferred to the water in form of heat. What is the temperature rise of the water? 2. how much the water temperature rises if the object lifts during it's...
  7. A

    Amount of Kinetic Energy Lost in Inelastic Collision

    1. Two carts, each of mass M, travel towards each other on a frictionless air track, one with velocity V, and the other with -3V. They collide and stick together. How much kinetic energy is lost in the collision? 2. P = mv, KE=1/2mv2 3. Initial KE of the system is the sum of the kinetic...
  8. L

    Where does an electron's kinetic energy go?

    When an electron moves through a wire between two terminals on a battery some of its potential energy is converted to kinetic energy. My question is, where does that kinetic energy go once it reaches the other terminal? Some of it is probably converted to heat, but what about the rest of it?
  9. S

    Kinetic Energy of a Rotating Bar

    Homework Statement A thin and uniform bar has a length of 2.00 m and weighs 12.0 kg. It is rotating from one end on a pivot 5 times every three seconds. What is its kinetic energy? This is its hint: break the bar up into infinitesimal segments of mass dm and integrate to add up the...
  10. K

    Finding Velocity with Kinetic Energy.

    Homework Statement I have to use energy conservation to solve this. So i cannot solve with kinematics "On a windless day, the engine of a 250 g toy rocket exerts 30N of thrust straight upward until it burns out at a height of 165 m" How fast is the rocket moving at 165m? Homework...
  11. R

    Kinetic energy of a projectile

    Homework Statement A 1kg mass is projected from the edge of a 20m tall building with a velocity of 20 m/s at some unknown angle above the horizontal. What is the kinetic energy (in J) of the mass just before it strikes the floor? Homework Equations K= 1/2 m v^{2} The Attempt at a...
  12. C

    MHB Collisions and loss of kinetic energy

    Could someone please check my answers so far for this question as its getting very messy so I'm not sure if I've made a mistake :/ Two particles of masses 2m and m are moving along the x−axis with constant velocities u1i and u2i respectively...
  13. F

    Why is Kinetic Energy not = mv?

    I guess I'm getting old and dumb but I'm having trouble with a basic physics concept, I'm sure you can explain it... Why is kinetic energy 1/2mV^2 and not mV? ***** Example of my confusion no1. Suppose person A has a mass of 1 and a velocity of 10 (on ice skates). Momentum = mV =...
  14. Pruddy

    The Rate at which kinetic energy changes to thermal energy

    A potential difference of 50 mV is maintained between the ends of a 9.70 m length of wire whose cross section area is 25.0mm^2. The conductivity of the wire is 6.80 x 10^6 (ohm.m)^-1. Determine the rate at which the energy in the wire is transformed into kinetic to thermal energy. 2. Homework...
  15. N

    Calculating the Kinetic Energy of a Meteor: What Factors Influence its Velocity?

    How can I calculate kinetic energy of a meteor? On what variables it depends? Thanks and sorry for my bad English.
  16. R

    Kinetic energy change during phase change

    hi all, its been hours that i could not find a decent answer for a 'simple' Q: during a phase change (say, boiling) the temp' doesn't change, as we all know. we also know that the temp' is a measure of the system kinetic energy (KE). im interested to know how the average KE AND its...
  17. Sneakatone

    Find watts from rotational kinetic energy

    a)I used the equation KE=1/2Iw^2 I=mR^2 ---> 1.5x10^30*20000^2 w=2.1*2pi KE=1/2(1.5x10^30*20000^2)(2.1*2pi)^2=5.2x10^40 J t=2.1 rev/s / 1.4x10^-15 rev/s^2=1.5x10^15 seconds 5.2x10^40 J/1.5*10^15 seconds =3.4x10^25 watts B)1.15*10^15 s=1.1*10^18 years I feel like this method is...
  18. M

    Kinetic energy question. (layman)

    Hi all. English is not my native language, so bare with me (joke i found googling the right word). I am from Argentina. My question. If i throw a ball, i have learned it has kinetic energy. But if motion is relative doesn't that mean that my hand has the kinetic energy too? thanks.
  19. S

    Kinetic Energy Formula definition explanation

    Homework Statement I'm trying to understand how this equation was came together, mainly, I hardly understand why velocity is squared, and why there's the constant of '1/2'. Homework Equations In classical mechanics, the kinetic energy of a point object (an object so small that its mass...
  20. H

    Calculating Energy Loss (Kinetic Energy) and Output

    Homework Statement Hey everyone, trying to finish up a report and having a problem with getting to the final answer. It is a final report on hydro kinetic energy. We are planning to install a hydro kinetic turbine under a bridge and calculate what the energy output would be in KW. I am...
  21. M

    Relating Momentum to Kinetic Energy

    We recently started going over momentum in my phyics class and we were given this bit of information: ##impulse=FΔt=mΔv=momentum## I noticed that I were to take the integral of both sides with respect to velocity, it would yield ##FvΔt=Fx=(1/2)mv^2## Which is the Work-Kinectic energy...
  22. F

    Conservation of momentum and conservation of kinetic energy

    Homework Statement Here is the problem: http://www.chegg.com/homework-help/questions-and-answers/7-blocks-collide-elastically-frictionless-surface-write-conservation-momentum-relation-thi-q237700Homework Equations There is conservation of momentum involved along with conservation of kinetic...
  23. Sneakatone

    Find kinetic energy from center of mass.

    two automobiles each of mass 1200kg traveling a the same direction. Speed of one automobile is 29.0 m/s and the other is 19 m/s. Regard these automobiles as a system of two particles. a)what is translational energy of center of mass? I found velocity at center of mass which is 24 m/s and...
  24. B

    The relation between atoms' kinetic energy and the energy levels

    Regarding the relation between atoms' kinetic energy and the energy levels of their electrons upon excitation: In other words, what really happens when an atom is excited, either by radiation or by collisions, or otherwise ? What are the mechanisms under which the transferred energy goes to...
  25. Sunil Simha

    Confusion Regarding Most Probable Kinetic Energy of an Ideal gas

    Homework Statement Find the most probable kinetic energy of an ideal gas molecule. Homework Equations v=sqrt(2RT/M) where v= most probable velocity k= Boltzmann's constant T= temperature of the system M= molar mass of the gas Maxwell's formula of...
  26. K

    Kinetic Energy and Work Homework Help

    Homework Statement A 50 kg mass is pulled at a constant speed up a 20° incline which is 12m long and 4.1m high. μk = 0.32 a) find the work done by tension, T. b) find the work done by friction. c) find the work done against gravity. Homework Equations W = F x D Work = force x...
  27. K

    Kinetic Energy and Work Homework Help

    Homework Statement While merging onto a freeway, a 1900 kg car accelerates from 17 m/s to 33 m/s What power did the engine supply? W = 7.6 x 105 J F = 9500 N Homework Equations P=W/T The Attempt at a Solution Not sure how to find T.
  28. K

    Kinetic energy of electron & energy states

    Homework Statement Use the relationship kinetic energy E = p^2/2m to show that the energy E_{0} of an electron of mass m in its lowest energy state is given by E_{0} = h^2/8mL^2 Homework Equations E = p^2/2m E_{0} = h^2/8mL^2 The Attempt at a Solution I've stared at this...
  29. A

    Kinetic Energy in water and the rate carried across each square meter

    [b]1. Consider an ocean current flowing at 2.5m/s a) How much kinetic energy is contained in a cubic volume of water that measures 1m on each side? The density of seawater is about 1030kg/m3 b) If the flow is perpendicular to one of the cube faces, what is the rate at which the current carries...
  30. M

    Kinetic Energy in Spherical Coordinates

    Homework Statement Derive the expression for kinetic energy of a classical particle in spherical coordinates. Homework Equations I believe the answer I am supposed to reach is: T=\frac{1}{2} m (\dot{r}^2 + r^2\dot{\theta^2} + r^2\dot{\phi ^2}sin^2\theta) The Attempt at a Solution...
  31. K

    Kinetic energy of water pouring

    Hello. It's not a homework but it is kind of exercise. I was wondering what's the kinetic energy of water flow (for a certain amount) from a faucet. But I'm not sure if I got it right. So I counted how much volume of water is dropped in 30 seconds. It turned out it's about 5.6liters. m=5.6kg...
  32. N

    Glancing Collision and Kinetic Energy

    A mass m1 = 6.20 kg is moving North with a velocity of v1 = 13.5 m/s when it collides perpendicularly with another mass m2 = 4.40 kg moving East with a velocity of v2 = 8.80 m/s. Mass m1 runs into mass m2 in an inelastic collision and both masses stick together and move off after the collision...
  33. N

    Collision and Kinetic Energy Problem

    A ball, which has a mass of m1 = 2.50 kg., is moving with a velocity of 8.00 m/s at an angle of 25.0˚ South of West. It collides with a second ball, which has a mass of m1 = 1.20 kg., which is moving with a velocity of 4.75 m/s at an angle of 61.0˚ North of West. They stick together and move as...
  34. S

    Kinetic Energy Transfer in Relativity: A Puzzler

    I wasn't sure whether this question belonged in relativity or QM, or even just plain classic. This forum seemed the best bet, but I am not using speeds near C - mere Galilean relativity will suffice here. I have two objects, A and B A is moving with velocity V and thus has kinetic energy E...
  35. M

    Exploring the Paradox: Why Does q Lose Kinetic Energy?

    Look inside the paint doc. My question is why does the paragraph say ...A positive charge q gains kinetic energy as it falls towards the negative plate... However the graph shows that the positive charge q loses kinetic energy... I am confused what am I not understanding?
  36. G

    Kinetic energy of a block sliding down a ramp

    Homework Statement You observe that after sliding down a distance of 2.61 m along a 5 m long track that is inclined at 20 degrees to the horizontal, a block of wood has a velocity of 0.13 m/s. If the coefficient of kinetic friction between the wood and the surface of the track is 0.40, what...
  37. A

    Kinetic energy of ball sliding down slope with electric field?

    Kinetic energy of ball sliding down slope with electric field?? Homework Statement As shown in the figure above, a positively charged ball is placed at point A and slides down the slope from rest. The area has a uniform electric field E = 26.1 N/C, pointing to the right. The mass of the...
  38. H

    Kinetic energy from plate A to plate B

    Homework Statement An electron acquires 3.45x10^(-16) J of kinetic energy when it is accelerated by an electric field in a computer monitor from plate A to plate B. What is the potential difference between the plates, and which plate is at the higher potential? Homework Equations...
  39. R

    Calculating work done by helicopter/gravity, kinetic energy and speed?

    A helicopter lifts a 90 kg astronaut 13 m vertically from the ocean by means of a cable. The acceleration of the astronaut is g/12. How much work is done on the astronaut by (a) the force from the helicopter and (b) the gravitational force on her? Just before she reaches the helicopter, what are...
  40. J

    Positive pion decay and kinetic energy

    Homework Statement A nucleus contains Z protons that on average are uniformly distributed throughout a tiny sphere of radiues R. Suppose that in an accelerator experiment a positive pion is produced at rest at the center of a nucleus containing Z protons. The pion decays into a positive muon...
  41. J

    Kinetic energy and speed of system of charges (electric potential)

    Homework Statement A square of side s has a point charge at each corner. They all have the same charge +q, but different masses, m1, m2, m3, and m4, respectively. Initially, all of the charges are held at rest until they are released. Of course, they would repel each other and move away from...
  42. J

    How Is Deuteron Kinetic Energy Related to Plasma Temperature in Nuclear Fusion?

    Homework Statement A deuteron, , is the nucleus of a hydrogen isotope and consists of one proton and one neutron. The plasma of deuterons in a nuclear fusion reactor must be heated to about 3.01×108 . What is the rms speed of the deuterons? What would the temperature of the plasma be if the...
  43. L

    Is the kinetic energy of an electron the same in all frames reference?

    Homework Statement Is the kinetic energy of an electron the same in all frames of reference? Homework Equations I think that the kinetic energy of an electron is E = hc / λ. However, I am not sure: I got this from searching Google rather than learning it myself. The Attempt at a...
  44. K

    Can kinetic energy be added linearly?

    According to special relativity, velocity cannot be added to another velocity linearly. But I was thinking, what about kinetic energy? K.E. = mv2/2. As velocity increases, the object's mass also increases. The way I see it, the increase in mass "compensates" for the less-than-expected increase...
  45. C

    Ehrenfest theorem for kinetic energy

    In classical mechanics, the time derivative of the kinetic energy of a particle is given by the particle velocity multiplied by the force. Specifically, in one dimension, this translates into: (d/dt)(p^2/2m)= −p/m ∂V/∂x I'm unsure how to prove this...
  46. Z

    Kinetic Energy of a sphere due to uniform line of charge

    Homework Statement A very small sphere with positive charge 6.00uC is released from rest at a point 1.20cm from a very long line of uniform linear charge density 4.00uC/m.What is the kinetic energy of the sphere when it is 4.80cm from the line of charge if the only force on it is the force...
  47. D

    Pile driver question kinetic energy and potential energy

    [b]1. a pile driver of mass 250kg is allowed to fall from rest through a distance of 2m on to a 400kg steel pile to drive it into the ground. Each impact drives the pile into the ground by 150mm. assuming that the pile driver remains in contact with the pile after impact and that momentum is...
  48. J

    Kinetic Energy and Time Problem

    Homework Statement A ball with mass m projected horizontally o the end of a table with an initial kinetic energy K. At a time t after it leaves the end of the table it has kinetic energy 3K. What is t? Neglect air resistance. (answer: (2/g)(√K/m) Homework Equations E = 1/2 mv^2 The...
  49. N

    Kinetic energy, Potential energy and change in water pressure

    Homework Statement I'm not particularly confident with my calculations and I would appreciate any feed back. A) What is the kinetic energy of an object with: mass = 5lbm velocity = 200 ft/sec B) What is the potential energy of an object with: mass = 5lbm height = 200ft g = 32.2...
  50. K

    Acceleration and Kinetic Energy

    Homework Equations a=F/m Ek= 1/2mv^2 --- Not exactly sure how to go through with this.. I tried finding velocity with the given kinetic energy, but am unsure what to do next.
Back
Top