Tagged Questions
1
vote
2answers
134 views
What does it mean if a body has kinetic energy?
What does it mean if a body has kinetic energy?
Does it mean that the momentum vectors of each particle of that body has the same direction?
What about angular momentum?
0
votes
2answers
145 views
Perpendicular Elastic Collision (different masses, different velocities)
I'm stuck on a mechanics problem and I can't make any headway past momentum and kinetic energy being conserved. Here is the problem:
Two hover cars are approaching an intersection from ...
1
vote
1answer
55 views
Fundamental properties of motion
The first paragraph of the Wikipedia article on the angular momentum operator states that
In both classical and quantum mechanical systems, angular momentum
(together with linear momentum and ...
-1
votes
1answer
58 views
Determine KE of electron given momentum & mass [closed]
Some info:
wavelength of electron: $2.78 \times 10^{-10}$
momentum of electron: $2.38 \times 10^{-24}$
Determine KE of electron. In a provided hint: $KE = \frac{p^2}{2m}$. So I have:
$$KE = ...
0
votes
5answers
173 views
Why is momentum conserved (or rather what makes an object carry on moving infinitely)?
I know this is an incredibly simple question, but I am trying to find a very simple explanation to this other than the simple logic that energy is conserved when two items impact and bounce off each ...
0
votes
1answer
151 views
Definition of energy
What is the definition of energy $E$ given a dispersion relation $\omega=\omega(k)$ where $k=|\vec k|$ and $\omega$ is not necessarily linearly proportional to $k$? What about momentum $\vec p$?
This ...
1
vote
1answer
261 views
Nuclear reaction: creation of deuterium
A proton p collides with a neutron(at rest) n at relatively low-energies and creates a 'deuterium-core' d:
p+n->d+γ
Find the wavelength for the photon as a function of the proton's momentum and the ...
5
votes
1answer
146 views
Impulse from absorbing a photon? Is there an increase in rest mass?
I'm going through A P French's special relativity. In one chapter (6) the following is set up:
Suppose that a stationary particle of mass $M_0$ is struck by a photon of energy $Q$, which is ...
5
votes
2answers
244 views
Intuitively Understanding Work and Energy
It is easy to understand the concepts of momentum and impulse. The formula $mv$ is simple, and easy to reason about. It has an obvious symmetry to it.
The same cannot be said for kinetic energy, ...
0
votes
0answers
26 views
Elastic Collision Between Two Objects [duplicate]
Possible Duplicate:
Elastic Collision And Momentum
I've already asked this question, Elastic Collision And Momentum, but I didn't find the answer particularly helpful--sorry, I don't mean ...
0
votes
1answer
320 views
Elastic Collision And Momentum
The question I am working on is, "Two blocks are free to slide along the friction-less wooden track shown below. The block of mass $m_1 = 4.98~kg$ is released from the position shown, at height $h = ...
5
votes
2answers
236 views
Photon energy - momentum in matter
$E = h\nu$ and $P = h\nu/c$ in vacuum.
If a photon enters water, it's frequency $\nu$ doesn't change.
What are its energy and momentum : $h\nu$ ? and $h\nu/c$ ?
Since part of it's energy and momentum ...
0
votes
1answer
123 views
Momentum And Energy Problem
The information to the question is, "A $59.0~kg$ boy and his $38.0~kg$ sister, both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backward with a velocity ...
0
votes
4answers
181 views
Find total energy and momentum of an moving electron in a rest frame
I have an electron moving with speed $u'$ in a frame $S'$ moving with speed $v'$ relative to a rest frame $S$.
How do I find the total energy and momentum of the electron in the rest frame $S$?
I ...
0
votes
0answers
248 views
Error Analysis, Change in momentum, Kinetic Energy
If momentum of an object is increased by 10%,then its kinetic energy will be increased by?
Well, I don't need the solution logically by calculating the change in Kinetic Energy etc, but my question ...
4
votes
3answers
499 views
Why do we need the quantity momentum?
Why do we need the quantity Momentum in physics when we have the quantities like Force and Energy? Isn't it possible to substitute the usage of Momentum with equivalent of Force and Energy?
-3
votes
1answer
136 views
Mathematical question on Collisions [closed]
A 2.5kg ball travelling with a speed of 7.5m/s makes an elastic
collision with another ball of ...
3
votes
1answer
1k views
How do kinetic energy and linear momentum relate?
It took me quite a long time to click my gears in place and even then I'm not sure it's completely correct.
The problem is that I need to understand these concepts (physics concepts; not just these ...
4
votes
3answers
339 views
Conservation of Energy and Momentum Regarding Forces - clarification needed
The other day, my teacher stated something along the lines of, "Conservation of momentum is not violated by the actions of internal forces, but the conservation of energy is violated. Energy is ...
2
votes
0answers
252 views
kinetic energy in collisions
We were hoping you could help us understand collision energy.
Vehicle A is driving West at 35mph and weighs 1437kg.
Vehicle B is driving North at 35 mph and weighs 1882kg.
Vehicle B crashes into the ...
1
vote
2answers
235 views
Connection between momentum and energy
What is the connection between momentum and energy?
Which of the answers is the correct?
A particle can have zero momentum but energy.
A particle can have zero energy but momentum.
...
-1
votes
1answer
253 views
Minimal kinetic energy during elastic collision [closed]
Two wagons, moving towards each other along a straight line, collide. The first wagon has the speed 3 m/s and the weight 3 kg. The second wagon has the speed 1 m/s and the weight 1 kg. The collision ...
0
votes
2answers
255 views
Kinetic energy absorbing in order to avoid damages?
is this possible? To absorb kinetic energy and disable inertia force?
http://www.youtube.com/watch?v=KnKPbAbJI0w
http://www.youtube.com/watch?v=4_5oseSVUc4
3
votes
2answers
910 views
Conservation of Momentum/Energy collision Problem
I'm working on a physics problem in preparation for the MCAT and there's this particular problem that's troubling me. I don't know if it's a bad question or if I'm not understanding some sort of ...
1
vote
2answers
109 views
Is stopping something work?
If somebody pushes against a mass moving with $3 \frac{m}{s}$ to slow it down to $2 \frac{m}{s}$, he will drain the moving system of kinetic energy. Does he do work then or does he consume work?
My ...
12
votes
4answers
578 views
Energy is actually the momentum in the direction of time?
By comparatively examining the operators
a student concludes that `Energy is actually the momentum in the direction of time.' Is this student right? Could he be wrong?
2
votes
2answers
3k views
Difference between momentum and kinetic energy
From a mathematical point of view it seems to be clear what's the difference between momentum and $mv$ and kinetic energy $\frac{1}{2} m v^2$. Now my problem is the following: Suppose you want to ...
5
votes
2answers
5k views
What is the relationship between kinetic energy and momentum?
I can't seem to figure out the relationship between $E_k$ and $p$ or $F$.
I understand that the units are pretty different. But for example:
A bullet with a mass of 10.0g is moving at the speed of ...
7
votes
9answers
853 views
How to explain independence of momentum and energy conservation in elementary terms?
I'm trying to explain to someone learning elementary physics (16 year old) that linear momentum and energy are conserved independently. I'm not a professional physicist and haven't tried to explain ...
4
votes
3answers
2k views
Is the giant Newton's cradle in the Kit-Kat ad feasible?
Apologies in advance if this is too basic a question for physics.stackexchange. I don't want to dumb down this venerable institution. :)
My wife and I just watched this TV ad for Kit-Kat where a crew ...
23
votes
8answers
13k views
If photons have no mass, how can they have momentum?
As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
