Rest Definition and 558 Threads

Homework Statement A 30 kg wheel has a center of mass 0.1 m left from the center of the wheel and radius of gyration KG = 0.15 m. Find the angular acceleration if the wheel is originally at rest. The radius of the wheel is 0.25m. Homework Equations I=mk^2 T=f*d M=I*a Fn acting bottom in Y...

Hello. The speed of an elementary particle, for example an electron, in Zitterbewegung motion is c. So theory of relativity should say electron is massless particle ? Is Zitterbewegung not considered in theory in relativity ? Thanks.

The Electron Rest Mass is considered as a fundamental constant of nature. In relativistic Quantum Field Theory, in contrast, divergences arise. In order to deal with these divergences, one uses renormalization. According to this renormalization, the 'macroscopic' parameters of the lagrangian...

About 40 years ago, someone told me that free neutrons decay with a half life of around 14 minutes. About 10 years ago, I discovered that W bosons were involved, and that they are about 100 times as massive as a proton. Do W bosons really exist as "massive" particles for their very brief...

Please forgive me if this has been asked before. I understand that a clock that is moving relative to an observer at rest will slow down. If the moving clock is in a transparent rocket, would the stationary observer on the ground see the moving clock slow down physically?

Homework Statement [/B] A) Calculate the electric potential at point A. B) If a small charged particle with a mass m=5.0 mg and charge q=7.0 nC is released from rest at point A, what will be its final speed vf Homework Equations V=Kq/r Uelec=qV Uelec=1/2mv2 The Attempt at a Solution A) I...

Using these equations I am about to prove that photons have a rest mass of zero (mathematically) ________________________________________________________________________________________ E=hc/λ Photon Energy Equation E2=(pc+mc2)2 Mass-Energy Equivalence with Momentum Equation p=h/λ Momentum...

Hi, I'm trying to compute the differential decay of W boson at rest $$W^+ \rightarrow e^+ \nu_e$$ where the boson has fixed spin along z axis, and so specific cirular polarization. Using Feynman rules i get...

Let's see delocalized electron cloud on a surface of a metal (a piece of iron for example): When a strong Nd magnet get close the spin of these electrons allign to the magnetic field but the electrons don't move. Why? The force is not canceled out. Electrons should move and compressed in one...

Homework Statement A meteorite is approaching Earth at very high speed. In order to avoid an impact on earth, the world space agency has launched two space missions: one mission sends the astronaut Albert to the meteorite approaching earth. The other mission, lead by the space commander Trebla...

we use perfect fluid which is characterized by a energy density and isotropic pressure for general forms of matter. When guessing the values of energy momentum tensor indices we can use the physical insight that they are the flux of four momentum in a constant surface of spacetime. The...

Let's ignore gravity in this problem for simplicity. For a wheel rolling without slipping on some surface, the rest point is the point at a given instant of time that is in contact with the surface (the rest point has zero instantaneous velocity). If the wheel is rolling at constant velocity...

Title should be: Does rest mass increase in the FRW metric? The flat FRW metric can be written in conformal co-ordinates: $$ds^2=a^2(\eta)(d\eta^2-dx^2-dy^2-dz^2)$$ where ##\eta## is conformal time. Let us assume that ##a(\eta_0)=1## where ##\eta_0## is the present conformal time. Now the...

Homework Statement A particle with mass M at rest decays into two particles with masses ma=0.15M and mb=0.65M . i) Discuss the relative directions and magnitudes of the momenta of these two particles in the centre of mass reference frame. Homework EquationsThe Attempt at a Solution What's the...

I have seen this before, and just saw a thread about the sped of light. The problem is that they say, "light has no mass" then conclude incorrectly on a number of issues. What may be worse is that no replies seem to address the source of confusion, light does have mass, zero rest mass yes, but...

Homework Statement Homework Equations (Conservation of momentum) (Conservation of energy) The Attempt at a Solution I know linear momentum must be conserved on the X-axis, so mvo=mv1x+Mv2 where v1 is the final velocity of the small mass and v2 is the final velocity of the large mass...

Homework Statement A speeder moving at 120km/h passes a police car that immediately begins to chase, starting from rest, with an acceleration of 1.75 m/s2. How long is the chase? The answer is 38.1s Homework Equations d=v1+at2 At least that's what I tried, but it didn't work out right.., The...

Homework Statement The coefficient of static friction is 0.625 between the two blocks shown. The coefficient of kinetic friction between the lower block and the floor is 0.137. Force F causes both blocks to cross a distance of 4.46m, starting from rest. What is the least amount of time in which...

I have been studying that velocity = displacement / time. Now what if displacement / time always gives me same value - does it means that object is at rest as displacement is same then the body has not moved at all. So in above graph velocity is constant - ie displacement wrt to time is same...

Hey guys, this is not really a h/w question but I thought this would be the best place to get a relevant answer. So I was doing physics h/w last night and found that I could spin on my chair (a standard office swivel chair) by moving my arms in the opposite direction to the way I wanted to...

When I use E=mc2 to calc. the rest energy of an electron, I get .512Mev not .511Mev. I am using 9.109x10-31 kg for the rest mass of an electron and 2.9979x10^8 m/s for the speed of light in a vacuum. Can anyone tell me why there ís a discrepancy between my results and the accepted answer?

Hi everyone! So, I know that for a certain Synchrotron I have an output value of 1.5GeV/u for Uranium-238 particles, with a charged state of 28+ (## ^{238}U^{+28} ##). For this ion I would like to calculate the rest energy and the associated relativistic gamma factor. My approach was the...

Dear PF Forum, I just want to ask a simple question. Even if we are at rest (ignoring that the Earth rotates, evolves around the sun, orbitting SMBH and Milky way orbitting what? Virgo Supercluster? And Virgo Supercluster to what?), A. So even if we are at "rest" (blue line), are we always...

I do not know much about computers too (not really true but I am not really up to date), I do not know if I am doing what I am supposed to, here is my first simple question: Two connected pipes, equal diameter (internal) 100 mm, same height (2200 mm), I have water in one pipe at 2000 mm, in the...

I was wondering... can the rest mass of an object be time dependent? Like in a scenario where the body is losing mass? (Sorry I meant for a title "rest mass time dependent?")

In another thread a point was raised that current theory (or perhaps experimental results) establishes a definite (or appromimate) relationship between the average and the variance of the rest masses for the three flavors of neutrinos. I have tried to educated myself from material I can find on...

It could be that I'm misinformed, but I heard electrons at rest have magnetic fields. I thought that magnetic fields required a charge to be traveling at velocity before a magnetic field would arise. If this is the case could someone help me out? If an electron has a magnetic field at rest what...

There are two separate clocks, each set in a plane and on the ground. Assuming inertial reference frames, how can this be? Perspective of the observer in motion: The observer in motion on the plane will have recorded some time duration. Since the the world outside the plane is moving at a...

Homework Statement A man of mass m is on a still boat of mass M. the man jumps to the left so he has only horizontal velocity. Immediately afterwards the boat has velocity v. What's the work the man made. Homework Equations Conservation of momentum: ##m_1v_1=m_2v_2## Kinetic energy...

An electron rest mass in kilograms is calculated from the definition of the Rydberg constant R∞: where α is the fine structure constant and h is simply Plancks constant. Now, assuming the electron has an associated rest energy, Any idea on how this is calculated? I'm assuming using...

Homework Statement An electron moving with a speed v can behave as wave with wavelength 6.4 x 10^-15 m. Given that the mass of electron = 9.1 x 10^-31 kg and the charge of electron is 1.6 x 10^-19 C, find (a) the speed of v of the electron, and (b) the voltage needed to accelerate the electron...

Homework Statement I have a problem involving a goods lift with a cage m1 = 1500kg which is raised at V = 4m/s via a winding drum with a radius of 0.6m with the help of a counter weight of m = 900kg. i am asked to find the braking torque required to bring it to rest in 1 1/3 seconds. Also i am...

Homework Statement A ball, which is launched in the air with velocity V, has inelastic collisions with the floor: the kinetic energy after each collision is k times the kinetic energy before the collision, where k<1. Assume that the gravitational acceleration is constant: g [m/s^2]. I was asked...

Homework Statement What should be the spring constant k of a spring designed to bring a 1400 kg car to rest from a speed of 28 m/sec so that the occupants undergo a maximum acceleration of 5g’s? I have the solution manual and can see how they did this, but am curious as to why my attempt did...

Homework Statement Two electrons start at rest with a separation of 5.0 x 10^-12 m. Once released, the electrons accelerate away from each other. Calculate the speed of each electron when they are a very large distance apart (Ee = 0). Homework Equations EE = kQq/r Ek = (1/2)mv2 The Attempt at...

So a couple of days ago I ran into someone who said that an object traveling forever in a vacuum will eventually come to a stop due to deformation. After a little research I wasn't able to find much on the topic can someone explain it to me, and is it true that he object will eventually stop...

What equations can be used to compare the force of a resting X mass to the force of a smaller Y mass falling Z distance. Specifically, how much resting mass would equal the force of 300 pounds being dropped from 10 feet up?

Hi there, I'm trying to get a better intuitive handle on the concept of rest mass and rest energy - the energy term associated with rest mass. Introductory Physics textbooks often give statements along the lines of "mass is a form of energy" or "mass can be converted to energy" to explain...

Homework Statement weight of the box 10 kg on table at rest. Homework Equations deternmine weight of box and normal reaction acting on it. also determine w and Fn if force 40N pushes down the box. The Attempt at a Solution s i did like w=mg =NORMAL REACTION(R) and 40=10 * acceleration due to...

Homework Statement A 2.0-kg body moving along the x-axis has a velocity vx = 5.0 m/s at x = 0. The only force acting on the object is given by Fx = (–4.0x) N, where x is in m. For what value of x will this object first come (momentarily) to rest? Homework Equations 0.5 mv^2 = KE F*d = work...

When we say 938 MeV/c^2, is the speed of light already factored in? because I have read in some places where if you multiply this by c^2 you get the energy, and that is 938 MeV rather than 938* (2.998e8)^2 so when considering the rest mass of the proton, is the c^2 a variable, or a unit?

Homework Statement A solid cylinder of radius R is rolling without slipping on a rough horizontal surface. It collides with another identical cylinder which is initially at rest on the surface. The coefficient of restitution for the collision is 1.The coefficient of friction between the...

So gravity is supposedly caused by objects such as planets, stars, etc. resting on space which curves space. The more massive the object, the larger the bulge it creates, the stronger the gravity. My question is, why do these objects even rest on space in the first place? It's as if there's a...

A block is at rest on a ramp with an incline of 30 degrees above the horizontal. Find the force of static friction between the block and the ramp. One might be tempted to say that it equals the resultant force down the ramp: mg sin30. Or... A book is at rest on a table. What is the net...

Homework Statement a.) [/B]A proton and an "positron" (identical to an electron, except positively charged) are brought ##5µm## apart and released from rest. What is the initial potential energy stored by this system? b.) In all of the previous problems on this homework, the system's...

Hey, Say we have an object released at rest, separated by a certain distance..blah, blah, blah. When we use conservation of energy here, the kinetic energy would have a initial velocity right? So, K1+U1=K2+U2 assuming the object eventually comes to a rest...so U1 = 0, K2 = 0, so we would have...

Homework Statement A particle of rest mass m0 collides elastically with a stationary particle of equal mass and scatters at angle θ. The incident particle has kinetic energy T0 before the collision and T1 after the collision. (a) Show that T12 (2m0c 2 + T0) 2 = p02 p12 c4 cos2 θ. (b) Using the...

Homework Statement (a)Find Christoffel symbols (b) Show the particles are at rest, hence ##t= \tau##. Find the Ricci tensors (c) Find zeroth component of Einstein Tensor Homework EquationsThe Attempt at a Solution Part (a)[/B] Let lagrangian be: -c^2 \left( \frac{dt}{d\tau}\right)^2 +...

Homework Statement A particle of mass m, initially at rest at x=0, is accelerated by a force that increases in time as F=Ct2. Determine its velocity v as a function of time. Homework Equations x = vt v = at The Attempt at a Solution The correct method makes sense, but my method has no error...

1. Consider the situation shown in figure. Initially the spring is unstretched when the system is released from rest. Assuming no friction in the pulley, find the maximum elongation of the spring. https://drive.google.com/file/d/0B3FvaDRwJ2neQWtBU3JrazVTeEU/view?usp=sharing Homework...