Kinetic energy Definition and 1000 Threads

Homework Statement A ball with radius ##r## is inside a hollow cylinder with radius ##r+R##. In the first part of the assignment, one has to calculate the minimum kinetic energy the ball has to have at the bottom in order to complete a full loop in the cylinder. It turns out to be...

Homework Statement A proton has a speed of 0.2c. Find the speed of an electron that has (a) the same kinetic energy as the proton, and (b) the same momentum as the proton. Homework Equations K=ϒmc^2-mc^2 The Attempt at a Solution This is what I did for the same kinetic energy part, but I...

Hey guys, I need help with the following question. A lead ball of specific heat capacity 130J/KgK travels with a speed of 100m/s before it hits a wooden cube fixed to floor and gets stuck inside.What will be the rise in temperature of this lead ball by the time it comes to I attempted the...

Today I was doing some reading and I came across this topic. If we have a stationary hydrogen atom with a single electron in orbit around the nucleus and want to calculate the kinetic energy of the electron we would take the following approach. 1) Using Newton's second law: F = ma ⇒ FE = mac...

Hello Physics Gurus, Please critique the following logic... When a runner hikes/runs to the top of a mountain, the chemical potential energy inside the muscles transferred into the potential energy of the runner's body mass at the higher elevation (Pe = mass*gravity*height = mgh). Energy is...

Hi everyone, I've been systematically working through the exercises in my first year college textbook and have come up confused over this particular problem. I have a solution manual but it solves this problem differently than I did, though comes up with a similar answer. I've included my...

Homework Statement Two identical spheres A and B are kept on a smooth surface. They are given the same impulse I. The lines of action of impulses pass through the center of A and away from the center of B. Then: (A) linear kinetic energy of B will be less than that of A. (B) B will have...

The equation for momentum (potential energy) is PE=M*V. The equation for kinetic energy is KE=(1/2)*(M*V^2). You will notice that PE is the derivative of KE. and then you might add that M, simply Mass, is the derivative of PE. However, because M is simply a scalar quantity, and the other...

Homework Statement I'm actually making up my own problem here to try to resolve some confusion I'm running into on understanding kinetic energy and reference frames... Let's launch a potato of mass m (just call it 1) horizontally with a potato gun on a fast vehicle moving 50 m/s, while I'm...

Homework Statement The position of an object of mass 2 kg is changing as a function of time by the formula x(t) = 4t^3-6t. (a) find the work done by the forces acting on the particle between t=1 and t=3s. (b) What is the object's velocity when the force on it is zero? Homework Equations is...

I am really confused here. I have studied that if the kinetic energy of a moving body is not changing then the net work being done on the object is equal to zero. But when we are talking about a body moving upwards at constant velocity there is no change in its kinetic energy but there is still...

I'm confused; forgive me if this dumb. I'm trying to reason what "force" is, on a molecular level. I'm only concerned about normal forces here (pushes and pulls), not field forces. Forces in Newtons are vector quantities and only represent relationships between two things right? It isn't...

Homework Statement Homework Equations These are the equations he provided. The Attempt at a Solution I actually have no idea how to do them. So any help would be much appreciated.

Hello everybody, A special problem constrain me to make a variable change in my Hamiltonian operator, so with the kinetic energy operator, I have a doubt. The variable change is: ## \theta \longrightarrow (\theta + k) ## (where ##k## is a constant). And the kinetic energy operator...

Homework Statement A red van came through and crashed into a green van. The driver of the red van claims that he was driving at a speed of 11 meters/second at the moment of the crash. You want to find out if his claim is true. a. the mass of the red van is 1000 kg b. the mass of the green van...

It is my understanding that to calculate the change of kinetic energy of an object that speeds up from vi to vf you use this formula: Change of kinetic energy = 1/2 * m * (vf2 - vi2) When the initial velocity is 0 m/s I have no problems, but let's say an object that weighs 2 kg speeds up from...

College-level introductory physics textbooks usually devote a chapter to special relativity. Peter J. Riggs in his article appearing in the February 2016 issue of The Physics Teacher (pp 80-82) derives a couple of expressions for the kinetic energy of a massive (as opposed to massless) particle...

basically, as far as I know we can derive 1/2mv2 from ∫F⋅ds=1/2mv2=(p2)/2m for wave equation we use Hamiltonian H=P2/2m+V where P and V are both operators However, I wonder how we can say that P2/2m is the term for kinetic energy because ∫F⋅ds=∫(dp/dt)⋅ds=1/2mv2 is saying that knowing F and...

Homework Statement Two ice skaters of mass ##m = 50\,\mathrm{kg}## each are moving towards each other frictionless on parallel paths with a distance of ##3\,\mathrm{m}##. They both have a velocity of ##v_o=10\,\frac{\mathrm m}{\mathrm s}##. Skater 1 is holding a massless rod of length...

Homework Statement I have a bloc sitting on a horizontal table, and we shoot a ball through it. The speed right before entering the block is v and the speed when it exits the block is v/2. I need to prove that the fraction of the initial energy that is lost due to heat is 3/4 - γ/4, where γ is...

Homework Statement You push a blob of gelatin with a constant force of 2.4 F across a wet table on which it slides easily. Because the blob shape distorts, its center of mass moves only 33 mm during the time interval in which the point of application of your force moves 53 mm . By how much does...

Homework Statement Two 0.50-kg carts are pushed toward each other from starting positions at either end of a 6.0-m low-friction track. Each cart is pushed with a force of 2.9 N , and that force is exerted for a distance of 1.0 m. What is the kinetic energy of the center of mass of the system...

Homework Statement In solid state physics,we know all the states of free electrons can be expressed by the First Brillouin Zone. We know the $$E(k+K)=E(k)$$ where K is reciprocal lattice vector. We also know that the kinetic energy of the electron is $$E_{k}=\frac{\hbar^2k^2}{2m}$$. [/B]...

I saw another post about this but i didn't quite find what i was looking for there so i thought i'd give it a go instead with a thread. Homework Statement Calculate the exact value of the kinetic energy of the hydrogen atom in its ground state. No more information is given, we are referred to...

Homework Statement A 120 kg hoop rolls along a horizontal floor so that its center of mass has a speed of 0.240 m/s. How much work must be done on the hoop to stop it? Homework Equations I of hoop=MR^2 The Attempt at a Solution KE=0.5*m*v^2+0.5*(mR^2)(v/R)^2...

Homework Statement A.What is the change in kinetic energy of the crate? Answer in units of J. B.What is the speed of the crate after it is pulled 5.79 m? Answer in units of m/s Magnitude of work done by gravity= 200.786 Work done by applied force= 822.18 mass=8.91kg force pulling on box= 142N...

Homework Statement A 410 g particle in a semi-spherical bowl of radius 0.9 m is released from rest at point A at the level of the center of the bowl, and the surface of the bowl is rough. The speed of the particle at B is 2.6 m/s. The acceleration of gravity is 9.8 m/s 2 . What is its kinetic...

I remember throwing clay balls at walls in my childhood and observing them stick to the wall. In a more scientific perspective, considering the ball and wall as a system, I can say that the total momentum before collision is greater than 0. But then, after the collision, the kinetic energy of...

I am trying to find the most efficient way to convert kinetic energy to heat. The first thing I know is friction, however friction cause wearing for long term use. The second is convert to electric energy(dynamo) and then convert to heat using electric coil, however I think that has low...

Homework Statement Consider a gas of molecules of mass m at equilibrium at temperature T. Obtain an expression for the fraction of molecules having kinetic energy e = 1/2mC2 in the range e to e + de. This is problem 5.3, page 48 of Vincenti and Kruger's Intro to Physical Gas Dynamics Homework...

Homework Statement (a) Cobalt has only one stable isotope, 59Co. What form of radioactive decay would you expect the isotope 60Co to undergo? Give a reason for your answer. (b) The radioactive nuclei 21084Po emit alpha particles of a single energy, the product nuclei being 20682Pb. (b) (i)...

Homework Statement [/B] An ice skater executes a spin about a vertical axis with her feet on a frictionless ice surface. In each hand she holds a small 5kg mass of which are both 1m from the rotation axis and the angular velocity of the skater is 10rad/s. The skater then moves her arms so that...

I've added 'in classical physics' in the thread title because all the differences between them that I found on the internet involved relativistic physics. It was something like both momentum and kinetic energy being components of a four-momentum or something like that. But I cannot understand...

Homework Statement A disk of mass m1 is rotating freely with constant angular speed ω. Another disk of mass m2 that has the same radius is gently placed on the first disk. If the surfaces in contact are rough so that there is no slipping between the disks, what is the fractional decrease in the...

From Chris' perspective Bob is traveling with 1.5*108 m/s in direction a. Angelica is also traveling with 2.4*108 m/s in direction a. From Bob's perspective Chris is traveling with 1.5*108 m/s in direction b (The opposite of x). Angelica is traveling with 1.5*108 m/s in direction a. They all...

Homework Statement Hydrogen ions moving at various speeds are directed at a region of combined electric and magnetic fields as shown in the diagram below. The electric field is between two parallel plates 10 mm apart with a potential difference V across them, while the magnetic field of flux...

I'm having a bit of trouble conceptualizing this. I've looked all over the Internet, and I've been seeing that in completely inelastic collisions the reason that kinetic energy is not conserved is because energy goes into deformation, sound, propelling shrapnel, and especially heat (among other...

Homework Statement I have the decay K+ → μ+ + νμ Calculate: 1. Momentum of μ+ 2. Total energy of νμ 3. Mass of K+ 4. Speed of μ+ 5. Speed of νμ Homework Equations The only thing we get are the kinetic energy of μ+ so Kμ+ = 152.53 MeV and the mass of mμ+ = 105.658 MeV/c2 The Attempt at a...

Homework Statement Not actually a homework question but is an exercise in my lecture notes. Homework Equations I'm following this which demonstrates that the momentum operator is Hermitian: The Attempt at a Solution$$KE_{mn} = (\frac{-\hbar^2}{2m}) \int\Psi_{m}^{*} \Psi_{n}^{''} dx $$ $$...

Is the distribution the same as Boltzmann distribution? Have anyone made a mathematic equation for the KE of free electrons on a piece of metal?

Homework Statement A wooden toy mouse of mass (m) is attached to a spring with constant (k) and suspended vertically as shown below. The toy is released at the point the spring is unstretched at position x = +A, passes through equilibrium at x = 0 and the spring’s maximum extension occurs at x...

How should I look at the problem at stopping a moving object with the following conditions 1) mass m and speed v 2) 0.5 m and 2v 3)0.5m and sqrt 2 v Simple math tells me the number 2 would require more energy to stop it. I can relate to energy better in terms of how to stop a moving mass...

Homework Statement Ball 1 has an inertia of 0.500 kg and ball 2 has an inertia of 0.600 kg . Ball 1 is moving away from you at 5.0 m/s, and you decide to throw ball 2 at it to make it go faster. The balls collide head-on, and the coefficient of restitution for the collision is 0.95. Part A)How...

1. The problem statemees and given/known data A ball has a potential energy of 200J. Once the ball reached the ground, it's kinetic energy was 175J. Is this possible and does this defy the conservation of energy? Homework Equations KE = PE The Attempt at a Solution I am not sure. Being in high...

Homework Statement Homework Equations ΔKE=W+FcosΘd KE=.5mv^2 Final Vel^2=initial Velocity^2+2ax The Attempt at a Solution So calculate the force at x=2.6 to -5.356N, set 2.6(-5.356)=1.3Vf^2-1.3(0^2) which seemed to prove a problem as the square of the final velocity was negative, but just...

Homework Statement I need to accommodate a dashpot in an intentionally simple work-kinetic energy analysis method. For example, for a box being dragged up a ramp via a rope while attached to a spring, I can deal with the work done by gravity, rope tension, spring force, and friction via the...

Hi, I'm a high school science teacher. Most textbooks classify EM radiation as kinetic energy. But this doesn't seem right to me. As a photon is massless it's hard to see how it can have kinetic energy which is 1/2 mv^2. It could be said that it has energy hf and therefore mass hf/c^2. Then its...

When I learned about operators, I learned <x> = ∫ Ψ* x Ψ dx, <p> = ∫ Ψ* (ħ/i ∂/∂x) Ψ dx. The book then told me the kinetic energy operator T = p2/2m = -ħ2/2m (∂2/∂x2) I am just think that why isn't it -ħ2/2m (∂/∂x)2 Put in other words, why isn't it the square of the derivative, but...

1. Problem Statement: A worker lifts a heavy crate vertically 1.0 m in 2.0 s. If she lifts the same crate the same distance in 1.0 s, the work was done by her is A the same. B two times as great. C half as great. D four times as great. E one-fourth as great...

Homework Statement I really don't have a homework question just a thought. Is rest energy "maximum energy" for a particle? As to say a particle at rest has a given energy, so when it is in motion it transfers some mass energy to kinetic energy, where both the mass and kinetic energy together...