Kinetic energy Definition and 1000 Threads

  1. O

    How Does Beta Minus Decay Affect the Kinetic Energy of a Tin Nucleus?

    Hello everybody, I am a first year student and I have a question that I am not sure if I can answer. A radioactive isotope of Tin(50), with 85 neutrons in its nucleus and without any electrons bound to it, undergoes a beta minus decay. The electron pops into existence, 10-15m from the center of...
  2. C

    Rotational Kinetic Energy of Disks

    Homework Statement A disk with a mass of 4kg and a radius of 2m is free to rotate around an axis that passes through the center of the disk and perpendicular to the plane of the disk. The rotational kinetic energy of the disk is increasing at a constant rate of 20 J/rad; that is, the energy...
  3. A

    Kinetic energy of two different masses (ratio)

    Homework Statement Two masses, one of 20kg and the other of 40kg, are pushed using the same force on the same distance. What is the ratio of the kinetic energy? (Kinetic energy of 20kg/kinetic energy of 40kg) Homework Equations Ek=mv^2 F=ma v=at The Attempt at a Solution So, I...
  4. E

    Why Does Hot Water Freeze Faster Than Cold?

    Hi my name is Bruno, I'm 19, I'm currently finishing my 12nd grade on arts. I'm annoyed because no one I know can properly discuss the Mpemba effect with me. So, I'll go as fast as I can on this. The scenario. We have a cup of water let's say for example at 80 degrees Celsius ...
  5. O

    Why Does Integrating Relativistic Kinetic Energy Lead to Different Results?

    I am doing the integral DK = ∫pdv = mv/(√1-v2/c2)dv , in the same way as they do the ∫Fds = ∫mvdv if you separate the integrals. Where is my mistake and istead of (γ-1)mc2 I get -mc2/γ . I know that I am mistaken, I did see some equations but I don't get the 'theoretical' part.
  6. O

    Real gravitational potential energy to kinetic energy

    This isn't a homework problem, but something that has being buzzing in my head. I've been thinking about it cause at huge distances from Earth g changes and also in what happens for really dense objected and small things could change too. The real equation for gravity no matter which body...
  7. B

    Why is the Integral of Force Over dx Equal to Kinetic Energy?

    Hello, I was just wondering why the integral of force over dx becomes kinetic energy
  8. U

    Help understanding this Kinetic energy problem

    Homework Statement A 60kg ice skater is spinning around at 300 degrees per second. His radius of gyration is .5m. As he pulls his arms in he does 300 J of work. i.What is his initial kinetic energy? ii.What is his final kinetic energy ? iii.Assuming that his new radius of gyration is .32m...
  9. R

    Kinetic Energy and Moment of Inertia

    Homework Statement A hoop with mass m= 10 kg, radius r=0.6 m, and moment of inertia I=mr^2 is rolling without slipping with a linear velocity of 8.5 m/s. What is the total kinetic energy (in J). Homework Equations K=1/2 m v^2 Kr=1/2 I ω^2 The Attempt at a Solution The kinetic...
  10. fluidistic

    Expectation value of kinetic energy (QM)

    Homework Statement In a QM problem I must calculate the expectation value of the kinetic energy, namely ##\langle \Psi _c ,\frac{ \hat { \vec p } ^2}{2m} \Psi _c \rangle##. Where ##\Psi _c=ce^{-\alpha x^2}##. Homework Equations ##\int _{-\infty}^\infty \exp \{ -a x^2 +bx \} dx =...
  11. K

    Kinetic energy of wheel/tyre when braking

    I have been doing some working on braking energies, and have hit a bit of confusion with regards to the kinetic energy of the wheels and tyres. Obviously, the kinetic energy of the moving car itself follows the old rule of 1/2mv2. For a 1000kg car at 30ms that's then 450kJ. I have then...
  12. C

    Understanding the concept of Kinetic Energy

    Hi, I'm new to physics and have some trouble understanding the concept of Kinetic Energy. It's not that I don't understand the definition given to me, I do, but I don't feel the intuition behind the concept. Here's what I understood of the concept : Kinetic energy comes from moving objects (If...
  13. F

    Conservation Of Kinetic Energy Problem

    Homework Statement A body of mass 2.0 kg makes an elastic collision with another body at rest and continues to move in the same direction but with one-fourth of its original speed. What is the mass of the struck body?Homework Equations Conservation of Kinetic Energy EK = (1/2)*m*v^2...
  14. P

    How Does Weight Impact Momentum and Kinetic Energy in Air Track Experiments?

    Homework Statement Hello I've been doing this experiment which is about momentum and kinetic energy. I'm using an air track and using two carts one 3/4 of the way down with 50g weights I will add to it each time I test it this will be the variable i will be changing the cart will stay...
  15. E

    Conservation of Linear momentum and Kinetic energy

    Suppose that we are working with a horizontal string with two masses attached. There is no friction on the floor and we move those two attached masses away from the equilibrium position by an undefined distance. Once the string with those two attached masses passes through the equilibrium...
  16. C

    Why is kinetic energy 1/2 mv^2?

    This is probably a stupid question because the answer is likely "it just is". I am reading Calculus: The elements by Michael Comenetz, and when talking about mQ, he goes on to say "there happens to be advantage in working with 1/2 mQ rather than mQ itself", and then gives the equation k = 1/2...
  17. 1

    Kinetic energy efficiency question

    Homework Statement A roller coaster descends 55m from the top of the first high point to the first low point in the track. The roller coaster converts gravitational potential energy to kinetic energy with an efficiency of 50.0%. What is the velocity of the roller coaster at the bottom of the...
  18. 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...
  19. 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...
  20. 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...
  21. 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
  22. 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) -...
  23. R

    How Does Dropping a Heavy Object into Water Affect Its Temperature?

    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...
  24. 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...
  25. 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?
  26. 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...
  27. 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...
  28. R

    What is the Kinetic Energy of a Projectile Just Before Impact?

    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...
  29. 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...
  30. 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 =...
  31. 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...
  32. 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.
  33. 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...
  34. 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...
  35. 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.
  36. 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...
  37. 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...
  38. 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...
  39. 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...
  40. 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...
  41. 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...
  42. 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...
  43. 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...
  44. 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.
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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