Rest Definition and 558 Threads

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...

Hi, I have this particular question, to which i think my method is correct, though the answer from the book which this question is in gives different to mine. Please! any assistance will be very much appreciated! Question: A Rocket was launched directly upwards from rest. Its motors...

Hi, I'm studying Roman culture and civilizations in a course at my university and I'm learning how poets and philosophers argued that the natural state of matter is in motion, that everything is always in motion and never at rest, that there is an empty void that exists between objects and...

At the last scattering surface (LSS), the energy density of neutrinos is argued to be ~0.68 of the energy density of blackbody photons, based on a thermodynamic equilibrium argument. This is also required to obtain the correct total energy density for stable expansion. At that time, the average...

This question has been asked several times, but I don't want the answer (I can see the stupid answer...) I need help with my solution... Homework Statement A large aquarium of height 5.00m is filled with fresh water to a depth of 2.00m. One wall of the aquarium consists of thick...

[b]1. A person standing close to a railroad crossing hears the whistle of an approaching train. He notes that the pitch of the whistle drops as the train passes by and moves away from the crossing. The frequency of the distant approaching whistle is 555 Hz; it drops to 472 Hz after the train is...

Homework Statement A 2.0 kg block is released from rest on a frictionless 30 degree incline. After sliding 0.80 m it comes in contact with the spring, and after sliding an additional 0.20 m, it comes momentarily to rest. What is the spring constant? I knew that spring constant is equal to...

When one says they are at rest relative to the cosmic microwave background, does this mean that they are in a frame where the same frequency is measureed in all directions? Because, I could imagine if I boosted in one direction, then the spectrum behind me would be redshifted, and the spectrum...

A 1kg particle is in a potential given in joules by U(x)=4x2+5x-3, where x is in meters. The particle is initially at position x=1m and moving with velocity v=6m/s in the +x direction. Find the position when the particle first comes to rest. Here is my train of thought F(x)= -dU/dx...

Okay, so I have an astronomy/astrophysics exam tomorrow and I understand everything except for the local standard of rest. Could someone please explain it to me? Thanks!

Homework Statement A block with mass m = 3.57 kg is attached to a spring with spring constant k = 165.7 N/m and negligible mass. The coefficient of kinetic friction between the block and the table is µk = 0.239. The box is displaced from its equilibrium position to the left by 0.216 m. If the...

Penrose says in “Cycles of Time” that rest mass isn't exactly a Casimir operator of the de Sitter group, so a very slow decay of rest mass isn't out of the question in our universe. If rest mass is strictly conserved, should it be a Casimir operator of the de Sitter group? Decay of rest...

Homework Statement A sledge of mass m = 85 kg has initial velocity v0 = 45 m/s and is moving horizontally along a straight line. The net force acting on the sledge is solely due to air resistance and is given by F = −k v2, where the constant is given by k = 1.2 kg/m. Find where the sledge...

If the universe were expanding very, very rapidly, would rest mass disappear? I've been reading "Cycles of Time" by Roger Penrose, which is about his "conformal cyclic cosmology" theory. The gist of it is that in the VERY VERY distant future, like a googol of years from now, when all the...

[b]1. a 9.0 killogram mass and a 3.0 kg mass are at rest on a frictionless table. A massless spring is compressed between the masses, which are held together by a thread. The thread breaks and the 9.0 kg mass moves to the left with a velocity of 2.0 m/s. Find the velocity of the 3.0 kg mass...

long questions but only need a little help i think: 1) 3 particles A,B,C of masses m,2m,3m lie at rest in that orderon smooth horizontal table.the distance between each particle is a> A slack light inelastic string of length 2a connects A and B and an exactly similar slack string connects...

1. A body of mass 2kg is initially at rest and is acted upon by a force of (v - 4) Newtons where v is the velocity in m/s. The body moves in a straight line as a result of the force. 2. a. Show that the acceleration of the body is given by dv/dt = (v - 4) / 2 b. Solve the differential...

1. A skier starts from rest at the top of a hill of height h down a 30.0 degree ski slope with an acceleration a. a.) What is her speed at the bottom of the hill? b.) If the hill was h = 250. m high and her acceleration down the slope was a = 4.00 m/s2, what was instantaneous speed at the...

A train is traveling up a 4.4 incline at a speed of 3.10 when the last car breaks free and begins to coast without friction. How long does it take for the last car to come to rest momentarily? The way I approached it that I reduced the speed to its x and y components. But I don't know what...

this thought was inspired by the recent news about FTL neutrinos. of course i suspect their instruments are broken and that no such thing happened, but regardless, the question stands: it's easy to talk about the rest frame of classical objects where the notion of "trajectory" applies and...

This is a problem from my Calculus class in the sections about vectors. Homework Statement Two forces F1 = 2i + 6j and F2 = 2i -2j act on an object. What additional force is needed to keep the object at rest? Homework Equations I'm not sure where to start. The Attempt at a...

Homework Statement A car starts from rest, accelerates at a constant rate, has a displacement of x and a final velocity of v. What is the final velocity (in terms of v) if the displacement was 9x? Homework Equations v^2=vo^2 + 2a(x-xo) The Attempt at a Solution I have no idea. :(

If I moved in the rest frame of a solar neutrino would I still measure neutrino oscillations? Thank you for any help!

Wouldn't you be able to determine both the momentum and position of a particle at rest? Wouldn't a particle at rest behave only as a particle and not as a wave? Never mind I get it now you would never be able to observe a particle at rest.

http://www.washingtonpost.com/blogs/on-faith/post/attention-governor-perry-evolution-is-a-fact/2011/08/23/gIQAuIFUYJ_blog.html" I would tend to agree that belief in evolution is a good indicator of general understanding of science (or perhaps more accurately, that lack of belief in evolution is...

http://www.cbc.ca/news/politics/story/2011/08/22/layton-obituary.html" Regardless if your blue, orange, green, red, or apolitical, Jack was probably one of the most respectable Canadian politicians. My sincerest condolences both to his family and close friends. May you rest in peace Jack.

Problem XIV, page 18 ------>http://www.physics.princeton.edu/~mcdonald/examples/ph101_2006/learning_guide_ph101_2006.pdf A patient's leg is held in traction as shown in the diagram. The top and bottom pulleys are fixed, while the central pulley is not, but has come to rest at a position...

I'm having trouble resolving the contradiction between theories of the Cosmic Microwave Background, and Special Relativity. Einstein denied the existence of any absolute standard of rest. As einstein-online.info paraphrases: "In the real world, there exists no such state of absolute rest...

Homework Statement Two particles of equal mass M and equal net energy E are approaching each other at an angle of 90 degrees. Find the net energy of one particle in the rest frame of the other. Do not assume that the velocities are small compared to the speed of light. Homework...

This has been discussed in a number of threads and in FAQs. I was wondering what constituted a rest frame as nothing in the universe is at rest, if you work the figures out we are moving at around 2.5% c. In another thread I found out that at rest simply meant not accelerating. This means...

In a previous thread someone pointed me to DH's FAQ article on the Rest Frame of a Photon. In the article DH states, "Time and length cease to have meaning in the limit v→c. In that limit, all time and length intervals shrink to zero," and I've been thinking about the implications of that...

hey guys ...i've got a doubt.. when there is no absolute rest in the universe...how is rest mass defined?

Imagine a solid, non-conducting cylinder at rest in IRF K, with a positive spherical charge centered on one end and a negative spherical charge on the other end. Each charge experiences an electric force toward the other. The cylinder is compressed, but there is no torque. Let us say that the...

A car with a mass of 1200 kg accelerates from rest to 20 m/s in 6.0 seconds. What average power must the car produce to cause this acceleration? a. 5 kW b. 15 kW c. 30 kW d. 40 kW For this problem, I did (1200)(9.81) and got the force. Then I used d= (6 seconds) x ((0 +20)/2) to find...

Hello everyone, I have a project of mine where I need to find out the force that acts on a wheel to start it rolling and keep it rolling so I can then select the correct motor and gear box. I have not had to do this kind of physics for years and I am having trouble with this problem: If a...

What is CMB rest? The Cosmic Microwave Background is remarkably uniform -- the temperature of the light is the same from all directions in the sky to within about one thousandth of one percent! That is, if you first adjust for the effects of solar system/orbital motion. Solar system motion...

Homework Statement A stone is thrown straight up from the ground with an initial speed of 44.1 m/s . At the same instant, a stone is dropped from a height of h meters above ground level. The two stones strike the ground simultaneously. Find the height h. The acceleration of gravity is...

Homework Statement 2000Hz siren and worker are both at rest with respect to ground. What frequency does worker hear if the wind is blowing toward him from the siren at 12m/s? Homework Equations f'=f(v/v-vs) The Attempt at a Solution So since the worker is stationary, Vd in the...

Problem statement How fast must a neutron be traveling relative to a detector in order to have a measured kinetic energy that is equal to its rest energy? An "attempt" I know Ek = mc^2 - m0c^2 But if Ek = m0c^2, wouldn't the two terms cancel out from this equation? I am having trouble...

Homework Statement a 45kg child runs with a speed of 3.50m/s tangential to the rim of a stationary merry-go-round that has a momentum of inertia of 555 kg m^2, and a radius of 2.45m. when the child jumps off, the entire system begins to rotate. what is the angular speed of the system...

From my understanding E=mc2 shows that relativistic mass is equivilent to energy. And hence the conservation of relativistic mass is a restatement of the conservation of energy. Also from my understanding it also indicates that rest mass can be converted into photons. Also I think this...

Is amplitude always perpendicular to the rest axis? in a wavelength amplitude it the distance between either the crest or through from the equbilium line. then in the case of transverse vibration, what is its amplitude? thanks

Homework Statement m=10k h=12m F=200N Homework Equations a=v/t F=ma The Attempt at a Solution I cannot find the remaining equations to completely work the problem.

Homework Statement The free surface of a liquid at rest contained in a container of reasonably large size is always seen to be horizontal. Can we say that it is a consequence of i) the absence of relative velocity between the liquid and the container ii) the absence of relative...

I was hoping someone could point me in the direction of the best way to calculate the rest energy of a proton. I am a complete noob with the standard model, so please be gentle. My goal is to compare a calculation of the energy which accounts for the quark structure of the proton versus E=mc^2...

Bike and Car both accelerate from rest ("intermediate" problem) Homework Statement Basically, both a bike and car start from rest. The bike will not go any faster than (final velocity) 20 mi / hr. The car will not go faster than (final velocity) 50 mi / hr. However, at first, the bike is...

Homework Statement Q: The rest energy of a proton is 1501.10^-10J. Calculate its rest energy in MeV. Homework Equations The Attempt at a Solution

Why is it that simple balances always come to rest in a horizontal position when equal weights are placed on both ends? If the weights are equal, then (assuming that the distance from each weight to the pivot is the same) the torques produced by the weights are equal and opposite and the net...

So every particle with some mass, even if the mass is very, very close to zero has a rest frame. A neutrino, say, could sit right next to me. But a photon, a massless particle, of course, can't, it has to zip by with light velocity. But when I would reduce the mass of a particle slowly...