Rest Definition and 549 Threads

Homework Statement a)-The massive grinder for wood-pulp in a newsprint paper factory, which can render about a half Tonne of wood into a thin soup in less than a minute, is essentially a stone cylinder of radius 0.900 m and mass about 6.00 Tonnes. An enormous motor spins this cylinder on its...

In relativity, we do not talk about just space anymore, but space-time, with time being just another dimension. An observer A at rest in an IRF who considers himself at rest at t=0 x=0, has a far away clock at t=100 for example moving towards him, i would like to say at 1second per second, but...

Hello everyone, this is my first time posting to these forums, and my first time posting any online help regarding math. As you can imagine, this is a bit awkward and embarrassing for me. My textbook has no examples of the type of problem below and hours of googling has failed me. Hopefully...

Homework Statement A student stands on a bathroom scale in an elevator at rest on the 64th floor of a building. The scale reads 828 N. (a) As the elevator moves up, the scale reading increases to 919 N. Find the acceleration of the elevator. (b) As the elevator approaches the 74th floor, the...

Homework Statement A proton has an initial speed of 3.5×10^5 . What potential difference is required to reduce the initial speed of the proton by a factor of 2? Homework Equations KE=.5*m*v^2 EPE=q*V The Attempt at a Solution I did KE=.5(1.67x10^-27)(3.5x10^5/2)^2 and then divided...

Homework Statement A particle at rest with mass M decays into 2 particles, one with mass m1 and the other with mass m2. Use conservation of energy and momentum to show that E1=((M^2+m1^2-m2^2)c^2)/(2M)Homework Equations E=√((p^2)(c^2)+(m^2)(c^4))=γmc^2 p=γmv The Attempt at a Solution Energy...

1. Nellie Newton hangs at rest from the ends of the rope as shown. How does the reading on the scale compare with her weight? 2. ANSWER FROM BOOK. The scale will read half her weight. In this way, the net force (upward pull of left rope + upward pull of right rope rope weight = 0 3. Can...

A car speeding up from rest to constant accel. travels 100 meters in 6.04s. How far did it travel in the first 2.37 seconds? So I figure if I divide distance by time 100/6.04 it will give me the velocity 16.5m/s. And since distance = vt I would do d=15.6*2.37 which equals 37.03m but this is...

What does "rest" mean? If I throw a ball straight up, at its highest point, is it momentarily at rest? Its velocity is momentarily 0, but it is still accelerating.

Homework Statement A particle of rest mass m_0 and kinetic energy 2m_0c^2 and sticks to a stationary particle with rest mass 2m_0. Find the rest mass of the composite particle. Homework Equations Conservation of momentum and thus energy. E_{bef} = E_r + E_k = E_{aft} where Er is...

Feynman's Lectures on Physics has an interesting graphic in volume 3, page 7_3, "Fig. 7-1. Relativistic transformation of the amplitude of a particle at rest in the x-t systems.", see scan below. Say ψ is the wavefunction of a particle at rest in 3D space, ψ = exp[-iEt], hbar = 1. If I now...

Will the friction act on a body at rest. Do not take in the case of inclined plane.

At least that's what it seems. Nilequeen posted that earlier somewhere. story This seems equally interesting: More Refs: http://www.sciencedaily.com/releases/2012/07/120712141916.htm...

Homework Statement An object is falling from rest with air resistance modeled by $$kv_x$$. Where v_x is the object's velocity in the x-direction (downwards). Find an expression for the speed of the object as a function of time. Homework Equations $$mg-kv_x=m\frac{dv_x}{dt}$$ The...

This is from Hawking's Brief History of Time: I don't see why the black hole is cut off from the rest of the universe. The black hole is still there and it's still made of ordinary matter, just a more dense than other matter. Is it because time stops in a black hole? Or that nothing can...

It is said that the stress tensor \mathbf T for a fluid at rest is diagonal. Why is this? The fact that the fluid is at rest means there is no net force, i.e. the body and surface forces cancel each other: 0 = \mathbf F + \nabla \cdot \mathbf T, but from this condition is does not follow...

Homework Statement A bomb at rest with 1.0x10^4 J explodes into three pieces. The first piece is 1.0 kg and travels in the positive y direction with a velocity of 60 m/s. The second piece is 4.0 kg and travels in the positive x direction at 40 m/s. Find the third piece's mass, velocity, and...

Homework Statement A 1600 kg object is initially at rest 400 km above the earth’s surface. The object falls straight down and generates 8.3x10^8J of heat energy while descending to an altitude of 100 km. What is the velocity of the object at this altitude...

Bar collision with ground Homework Statement A uniform bar of mass m and length l has no angular velocity when the extremity A hits the ground without bouncing. If the angle α is 30º, what is the magnitude of v1, so that the bar rotates, around A, until it immobilizes on the vertical position...

Homework Statement A funny car accelerates from rest through a measured track distance in time 21 s with the engine operating at a constant power 240 kW. If the track crew can increase the engine power by a differential amount 1.0 W, what is the change in the time required for the run? I...

How did we come to the conclusion photon has no rest mass? Does photon have any mass(not talking about rest mass) while moving at usual c?

Homework Statement When the elevator is at rest, the scale reads W. Suppose the elevator now accelerates down-ward at a constant rate of 0.4 g. What is the ratio of the new scale reading to the value W of the scale reading when the elevator is at rest? Homework Equations Force...

When you have lots and lots to learn, how do you handle it all? Do you have a specific schedule that you stick to or are you more flexible? What works best for you? When you burn out, what do you do? How do you fit in everything? (thank you)

I was wondering, if the inflation of the universe can be compared to blowing up a baloon with, say, some ink dots on it representing matter, then, as the baloon grows in size, the ink dots should be getting bigger too since they are part of the same fabric. It does not seem to be the case in the...

My book says that if two objects collide completely inelastically, the rest mass of the composite is greater than the sum. I assume this happens because the objects heat up and this is counted in their energy. However, in other problems the book assumes the rest mass of objects/particles is...

Assuming there is a mass on a scale, and they move with the same velocity. I know mass increases for a moving object, but the scale's mass will also increase. So would the scale read any more than if they were both at rest?

Is there any physical object in the universe that is not in motion?

In the two-slit experiment, as I understand it, an interference pattern can be generated by sending many electrons (or photons) through the two slits one at a time, and the pattern itself gets built up over time. The explanation is usually this: A single electron travels as a wave and so...

Homework Statement a speeding motorist traveling at 130km/h passes a stationary police officer. the officer immeaditly begins pursuit at a constant acceleration of 9.3km/h/s (note the mixed units) how much time will it take for the police officer to catch the speeding motorist, assuming the...

Homework Statement An unstable particle called the pion has a mean lifetime of 25ns in its own rest frame. A beam of of pions travels through the lab with a speed of 0.60c. a) what is the mean lifetime of the pions as measured in the lab frame? b) how far does a pion travel ( as measured...

Homework Statement An aircraft has to make an emergancey landing on a runway without landing gear , if the aircraft lands at 40 m\s-1 and μ is 0.5 , How far the aircraft slides before it comes to rest ? Homework Equations X=2 μ g \ v2 The Attempt at a Solution 2 x 0.5 \...

a person moves a full sam's club shopping cart mass=80.0 kg from rest to a velocity of 1.30 m/s over a distance of 1.80 meters to secure a spot in check out line. A. find the time required to get the cart moving from rest to 1.30 m/s? B. Determine the change in the chart's momentum? c...

1) How can get work done on a photon because work done = kinetic energy it depends on mass, but the rest mass of a photon is zero 2) From this equation E=PC , does this mean E of a photon is 0 because P must be zero since it depends on mass?

"at rest" in Einsteinian relativity I'm just wondering what the concept "at rest" means in Einsteinian relativity. The common thought experiment of an observer on a platform (Albert) and an observer on a train (Henry), moving relative to each other, is often used to explain relativity. If we...

I am wondering what the rest energy (mc^2) is of 1 cubic meter of pure matter (no empty space). Thanks, Jake

So, I need to make an Excel spreadsheet that realistically models the motion of a toy rocket. I need to take drag, gravity, and thrust into account, keeping in mind that the latter two will be influenced by the change in mass. The equation for force I must use, then, is: F = ma + v(dm/dt)...

Homework Statement Does an object at rest have inertia? Homework Equations The Attempt at a Solution

Hello, Suppose, A and B is clocks at both end of train. A is at left and B is at right. Observer O is at middle of train at point M. Observer R is on platform. Train is at rest and O synchronize both clock. The clock is synchronized with respect to both observer. Now, train starts moving to...

Hi folks, I asked a form of this question in another forum and didn't get a satisfying answer. As I understand it, there is a time in the early universe (t < 10–12 s) when particles have not acquired mass. According to special relativity, massless particles travel at c. Also according to...

I'm new to physics, so I'm sorry if this is a dumb question. If a string cannot be point like, it has measurable spatial dimensions, then it must have mass. Well if a string was vibrating at the resonant frequency of a photon, and at rest it must have mass and therefore a nonzero rest mass. This...

The question is rather old but I am not sure if we have a final conclusive answer (I was not able to figure it out for myself, nor have I found consensus in the literature) 1) do free-falling charges in a static gravitational field radiate? 2) do charges at rest in a static gravitational...

Would it be possible that every rest frame is going through a force field so everything will be smaller on atom level and time goes slower too (Lorentz, Einstein) ? So that force field is the holder of the encapsulated ration distance / time (C) ... That would explain the unknown time...

Homework Statement Two particles of mass 4 and 5 kg (respectively) move towards each other. If the mass of the system is 20kg what can you say, qualitatively and quantitatively about the system in the center of mass frame? Homework Equations In the CM frame net momentum is zero...

Homework Statement An antique yellow statuette of a bird is suspended from a spring scale. The scale reads 11.81 N when the statuette is suspended in air, and it reads 11.19 N when the statuette is completely submerged in water. a. Find the volume of the statuette b. Is the bird made of gold...

Homework Statement A beam of unknown particles travels at a speed of 2.5 x 10^8 m/s. When the particles are moving at this speed, their average lifetime is found to be 7,3 x 10^-8 s. What is their average lifetime when at rest? Homework Equations Well, Lorentz transformation for time...

Lets say for a moment that everything that travels at speed below c has a rest frame.. All kinds of waves are produced from entities which has a rest frame... for example, Water waves produced from water surface which has a rest frame, similarly sound waves from physical objects, light...

Hello again! Another silly question from a silly engineer if you guys would help, please? Question is: do we know enough about how time flows (in a frame of reference at rest) to assume that it has always flowed at the same rate, ever since the first plank time after the big bang? I mean, I...

Why is the rest energy usually ignored in Schrodinger’s equation? (I am aware of Dirac’s later relativistic equation.) What is the justification? Wouldn’t it change the nature of the solutions to the last equation below if it were included? Well, ok, it won't copy my Word equations. Why...

Calculating the rest mass of Ra [simple!] Homework Statement Calculate the rest mass of 226/88 Ra.Homework Equations The Attempt at a Solution There are 88 protons and 138 neutrons. Therefore, (88*1.007276)+(138*1.008665)=227.8361u But the answer says 226.0254u. It also says 4/2 He is 4.0026u...

a 59 kg pole vaulter falls from rest from a height of 4.7 m onto a foam rubber pad. the pole vaulter comes to rest 0.34 seconds after landing on the pad. calculate the athlete's velocity just before reaching the pad. calculate the constant force exerted on the pole vaulter due to the collision...