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.
http://imgur.com/luj32IE 1. Homework Statement
A skier starts from rest at the top of a smooth incline of height 20 m as in Figure 2. At the bottom of the
incline, the skier encounters a horizontal rough surface where the coecient of kinetic friction between the
skis and the snow is 0.21.
(a)...
Homework Statement
[/B]
Our teacher has given us the weekend to go and work on the Egg Drop project. He's restricted us to 20g total mass and 6cm * 6cm * 30cm in size. Food, foam, bubble wrap is prohibited. Parachutes can be added but can not make it exceed 12cm * 12 cm * 30cm.
So that's what...
Homework Statement
A 100 kg person in space throws a 1kg sphere away from their body. The sphere starts from rest and ends up traveling 10 m/s away from the person. What is the kinetic energy of the person and the kinetic energy of the sphere? Is kinetic energy conserved?[/B]Homework Equations...
Homework Statement
A 15.0g bullet is accelerated from rest to a speed of 780m/s in a rifle barrel of length of 72.0cm
a)Find the kinetic energy of the bullet as it leaves the barrel
b)Use the work kinetic energy theorem to find the net work that is done on the bullet.
(this problem had part...
Hello! I'm new to this forum but ok let's get this started,
First I'll revisit the definition I know as physics; the study of nature in order to provide a reasonable(radical/rudimentary) explanation/reason. This I believe in is not quite how things are today, at school, with my teachers or at...
Homework Statement
Suppose a subatomic particle of mass m kg has kinetic energy K.E. a nJ and is moving southward toward a vertical wall. When the particle is distance d cm from the wall a magnetic field is turned on: it has magnitude b T and points upward. The particle turns westward so it...
Homework Statement
The work function for potassium is 2 eV. Consider light with wave length 3.6*10^-7 m hitting the potassium surface.
a) what is the stopping potential?
b) what is the kinetic energy and velocity of the fastest electrons emitted?
Homework Equations
KE_max = hf - Φ
q_e V_s =...
Homework Statement
A 'hammer' thrown in athletics consists of a metal sphere, mass 7.26 kg, with a wire handle attached, the mass of which can be neglected. In a certain attempt it is thrown with an initial velocity which makes an angle of 45 degrees with the horizontal and its flight takes 4...
Homework Statement
Suppose an atom of iron at rest emits an X-ray photon of energy 6.4 keV. Calculate the “recoil” momentum and kinetic energy of the atom. (Hint: Do you expect to need classical or relativistic kinetic energy for the atom? Is the kinetic energy likely to be much smaller than...
Homework Statement
Two blocks are hung by a string draped over a pulley, a 1.5-kg block on the left and a 3.0-kg block on the right. The two blocks start out at rest and at the same height.
A. What is the change in the gravitational potential energy of the system of blocks and Earth when the...
Homework Statement
A truck hauling a big tank of oil starts at position x=D (Chicago) and heads due west (–x direction) toward its destination at x = 0 (Des Moines). At Chicago, the total mass of the loaded truck is M and the mass of oil it is carrying is λM. (Thus M(1–λ) is the "tare" mass =...
Homework Statement
A small bullet is fired into a large piece of wood. After the bullet penetrates the wood, the assembly moves as one unit along a low-friction track in the direction of travel of the bullet.
A. After the bullet is stuck in the piece of wood, is the momentum of the wood (not...
Homework Statement
A uranium-238 atom can break up into athorium-234 atom and a particle called an alpha particle, α-4. The numbers indicate the inertias of the atoms and the alpha particle in atomic mass units (1 amu = 1.66 × 10^−27 kg). When an uranium atom initially at rest breaks up, the...
why we assume that velocity decreases linearly in a spring (i.e. if one end is fixed, then velocity of a particle (of spring) at x from fixed =vx/l where v is the velocity of the free end) and why does it hold good too when the spring (linear mass density) is non uniform...
EDIT: spring has...
Dear PF Forum,
I have a question in mind. But I'm not sure if this belong to SR forum, cosmology or classical physics.
So I post it here.
And perhaps as some of you might have known before or thought it over. It's about kinetic energy.
Supposed this...
A rocket, with a rest mass 1 ton.
And the...
I have a question regarding how to calculate kinetic energy. Let's say I was to find the kinetic energy of a ball shot at 180 m/s at a 45 degree angle. Do i simply sub in 180 as v (velocity) in the kinetic energy equation (1/2mv^2) or must it be split into components?
I've recently created a 3D motion generator (Anti-Gravity Transportation (AGT)) in 2D/3D design. unfortunately my current physics knowledge is not advanced enough to take this machine to its maxium potential. i can concieve perpultion and sustainable energy coming from this idea. my question...
I got a little bit confused while studying gravitational potential energy, particularly the expression for long distances: (-GMm/r). An exercise asks me for the velocity, period and radial acceleration for a 1000kg satellite that I wish to put into orbit. That's okay. But after that, I'm...
We know that If object is homogenius and small (like gold atom) we can use this equation to calculate total energy of object when it moves very slow due to speed of light.And the equation is ##1/2(m_1v^2+m_2v^2+m_3v^2...=1/2Mv^2##, ##(M=m_1+m_2+m_3...)## here v is small and we are talking about...
Hi,
I'm reading a high school textbook about mechanics. It's amazing how the author draws up the problems and solves them by introducing a new consistent concept.
Now I'm reading about collisions. He writes the conservation of momentum but the problem is that we have two unknowns in one...
I heard that proportionality of kinetic energy with square of velocity, ##E_k\propto v^2##, can be derived with help of quadratic forms.
It goes like: we guess that ##E_k\propto v^2## and we assume that momentum ##p\propto v##, then equation is valid in another inertial system. And so on. The...
Homework Statement
A charged particle (q = -8.0 mC), which moves in a region where the only force acting on the particle is an electric force, is released from rest at point A. At point B the kinetic energy of the particle is equal to 4.8 J. What is the electric potential difference...
Considering horizontal flow in a pipe (under the action of pressure forces only) if we focus on a fluid element we have a pressure gradient across the same i.e, a net pressure force will always act over the element that essentially maintains the flow.Now, in a region in the flow field if the...
For particle in the box wave function, it is the eigenfunction of kinetic energy operator but not the eigenfunction of momentum operator. So, do these two operators commute? (or it has nothing to do with commutator stuff?)
How about for free particle? For free particle, the wave function is...
Dear PF Forum,
I'd like to ask a question regarding a post in Relativity sub forum.
The formula for kinetic energy is ##E_k = 0.5mv^2##
Which makes sense. Because if we push/accelerate 1 kg object for 1 m/s2 for 8 meters, we'll spend ##E = N.m = 8 joules##
How much time do we need to do that...
Homework Statement
[/B]
A 2.0 kg ball moving with a speed of 3.0 m/s hits, elastically, an
identical stationary ball as shown. If the first ball moves away
with angle 30° to the original path, determine:
a. the speed of the first ball after the collision.
b. the speed and direction of the...
Homework Statement
2. Homework Equations [/B]
KE=1/2 mv2
The Attempt at a Solution
To calculate the kinetic energy of the ball just after it leaves the surface, I use the ratio of the centre of gravities of the ball at the two different heights. My working is (0.41/0.76)×0.75 which gives me...
Homework Statement
In the figure here, a block of ice slides down a frictionless ramp at angle θ=55.0 ˚ while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 54.0 N and is directed up the ramp. As the block slides down through distance d = 0.400 m along the...
Homework Statement
This is my first time posting here guys so correct me if I am wrong. This question was on my test and I wanted to know if I did it right. There is a block of mass m and it is moving at a certain velocity before pressing against a spring which compresses distance x.
Find...
Imagine two experiments A and B.
In experiment A I load a gun with a cartridge and shoot a bullet. Total energy in this experiment will be E(heat) + E(projectile). I include recoil in E(projectile). E(heat) in its turn will heat the muzzle and some air. Done.
In experiment B I do...
This is mostly a conceptual confusion I'm having, not a specific problem, so it didn't seem like it'd fit under homework problems.
I'm having trouble understanding when potential energy should or shouldn't be used in a energy conservation equation. When looking at a problem with a skier going...
I have always found the Newton's Cradle that my daughter bought for me fascinating. With the steel balls as identical as possible then the analysis of the process is simple. Both the momentum and kinetic energy are conserved (assuming negligible losses) on collision. The only way(?) this can...
Hi, new here, so I hope I'm doing this correctly. I'll keep this question as brief as possible, but it requires just a bit of setup. I'm not an engineer or physicist, but do have a more than decent layman's understanding. I've lately become fixated on the game of bowling (ten pin), and have...
hi
I have been given an assignment at school to look at various ways heat is transferred through liquids. I'm interested in looking more into the kinetic energy of molecules and how their vibration causes heat, I would like to know if there is a device I could use to record the frequency of...
I know there are some threads discussing about the Lorentz force equation but this is something different I came across and I couldn't find anyway to derive that formula.
To be specific I'm talking about a charged particles in a magnetic field, where F=vqB and everything that is moving has...
There is 14 km of tunnel of 7.7 m diameter, full of water traveling at 3.75 m/s,that represents approximately 8000 Megajoules of kinetic energy.
How? Calculate it to prove (Taken From Wikipedia under topic of "Water Hammer".
Homework Statement
Lets say we have a series of balls and an eggs. All items have equal mass but are traveling at different velocities.
Thus they have differing kinetic energies.
Now, for each 'ball' object we have, we want to find an egg object with a similar kinetic energy. Let's say...
Homework Statement
So I have a horizontal pulley positioned at the edge of table with a mass of .2kg hanging down from a height of .76meters, the other end of the string is attached to a wooden block of mass .25kg that when the .2kg weight is dropped the wooden block is pulled towards the...
Homework Statement
A body is moving on a horizontal plane which gradually turns to another plane forming an angle ##α##. Friction coefficient is ##μ##. Find the kinetic energy of the body after the turn if in the beginning it was ##K_o##.
Homework Equations
Newton's laws.
The Attempt at a...
Homework Statement
Homework Equations
Please see below.
The Attempt at a Solution
I'm pretty sure my method is correct but I'm getting small answers:
$$
COM \\ \\
E_{6}= E_{2}+E_{\alpha}
\\
\\
Minus \ E_{2} \ and \ square \ both\ sides\\
\\
E_{6}^{2}+E_{2}^{2}-2E_{2}E_{6}=E_{\alpha}^{2}\\...
Homework Statement
Hi,I have been struggling on this problem for a whole day,looking for someone to sort it out!
My question:(please see the attached diagram as well)
Consider 2 spheres A and B,having different masses (m and M) but equal in size.
A is moving to the right at a speed u, B is...
Homework Statement
So first the task:
Determine the average value of the kinetic energy of the particles of an ideal gas at 0.0 C and at 100 C (b) What is the kinetic energy per mole of an Ideal gas at these temperatures.
I took the above right out of the pdf we got from our professor.
I know...
Homework Statement
A truck is moving at constant velocity v0 with a box of mass m on it. Suddenly it starts decelerating until its velocity becomes zero. Between the box and the truck the is a force of friction and the deceleration of the truck is sufficiently slow to allow the box not to start...
I am having trouble deciding when to use which equation.
If you're given the wavelength of a proton, let's say 100 fm, and have to find the kinetic energy of it, how would you do this?
Here are my ideas:
Idea 1: Use lambda = h/p, where p = sqrt(2Em).
Idea 2: Use E=(pc)^2+(mc^2)^2 =...
Homework Statement
Homework Equations
Q = c m ΔT
The Attempt at a Solution
so converting 55 mph to meters per sec gives me a velocity of 24.58 m/s
kinetic energy of car is 1/2 m v2
i set 1/2 m v2 = c m ΔT
plugging in v and c and masses of both
ΔT = 134.56
is that correct?
Homework Statement
A bullet of mass 2.0 * 10-3 kg is fired horizontally into a free-standing block of wood of mass 4.98 * 10-1 kg, which it knocks forward with an initial speed of 1.2 m s-1.
(a) Estimate the speed of the bullet.
(b) How much kinetic energy is lost in the impact?
(c) What...
Homework Statement
The problem is that my teacher asked to solve this using kinetic energy but i doubt it uses kinetic energy... i thought it uses potential energy.
[/B]
You put your little sister (mass m) on a swing whose chains have length L and pull slowly back until the swing makes an...