Rest Definition and 549 Threads

Homework Statement The system is released (m2) from rest and mid AB How can I show that he system comes to instaneous rest when m2 has fallen a distance of (4am1m2)/(4m1^2-m2^2)? Homework Equations The Attempt at a Solution

I'm currently taking Differential Equations, a senior-level American Revolution course, and an Intermediate Macroeconomics course. I'm also working half-time. I'm not doing as well as I would like in DE - essentially a "B-" on the first exam. I just had an exam yesterday, and I think I did a...

Homework Statement A train is traveling up a 3.73 degrees incline at a speed of 3.25 m/s when the last car breaks free and begins to coast without friction. a) How long does it take for the last car to come to rest momentarily? b) How far did the last car travel before momentarily coming to...

Homework Statement A rocket moves upward, starting from rest with an acceleration of 32.2 m/s2 for 5.84 s. It runs out of fuel at the end of the 5.84 s but does not stop. How high does it rise above the ground? Homework Equations I do not know. All equations I have tried have been...

I'm only at the end of the second year (out of 5) of a physics bachelor. I plan on to do a Phd although I've absolutely no idea in which area (and I know the admission will be very hard). After the Phd I'd like to do research for the rest of my life. Is that possible in the US? For example...

From my reading i am seeing the answer But according to special relativity, light ALWAYS travels with the light speed c, and is NEVER at rest and from this statement i am supposed to gather there is no rest mass. But logic tells me just because light is never at rest, doesn't necessarily...

A weight of mass 12.5 Kg hangs from very light pulleys as shown in fig. What force must be applied to the rope so that the mass stays at rest. M=12.5 Kg W=mg a=g=9/8 m/s^2 M=12.5 Kg W = mg = 12.5 x 9.8 = 122.5 N I've done this much but I have no clue what to do now. Can someone please...

Homework Statement The plastic tube has a cross-sectional area of 5.00 cm². The tube is filled with water until the short arm (of length d = 0.800 m) is full. Then the short arm is sealed and more water is gradually poured into the long arm. If the seal will pop off when the force on it...

Homework Statement A car is stopped at a traffic light. It then travels along a straight road so that its distance from the light is given by x(t) = bt^2 - ct^3, where b = 2.30 m/s^2 and c = 0.120 m/s^3. How long after starting from rest is the car again at rest? Homework Equations...

Homework Statement perform a calculation for an object moving vertically in air under gravity and experiencing a retarding force proportional to the square of the objects speed. see (W=.5(cwpAv2) Object is dropped off a 100 meter building from rest. radius of object = .0366m mass = .145...

Why does a non head on collision between objects with momentum and an object without momentum result in a 90 degree split? (objects have similar mass) Could you please represent this in vector form? I'm not sure how I could represent this because it's not a head on collision but a side swipe...

I'm reading Concepts of Modern Physics by Beiser, and the chapter example says: A spacecraft is moving relative to earth. An observer finds that in one hour, according to her clock 3601s elapse on the spacecraft 's clock. What is the craft's velocity relative to earth? (This is not a...

How do you define "at rest" in the Universe? I was reading in a Scientific American an article called: "Misconceptions about the Big Bang" By Charles H. Lineweaver and Tamara M. Davis. In it I found this: Individual galaxies move around at random within clusters, but the clusters of...

Hi! I'm pretty much a pop science guy so I can't say I know much about the underlying math or physics, but after listening to these lectures about pretty much everything over and over again, there is one thing I just can't seem to find the answer to. The explanation of red/blue shift is...

Consider a 4-coordinate system x=(x^0,x^1,x^2,x^3), x^0 plays a role of time, x^1, x^2, x^3 are some kind of space coordinates. In what follows greek letters will be 1,2 or 3, latin will be 0,1,2,3, c = 1, proper time squared ds^2 = g_{ik}(x) dx^{i} dx^{k}. Now, if the body is "at rest" we...

lambda = h/mv v -> 0 means lambda is -> infinite? So if I have an old pickup truck that moves really slow, its matter wave is huge, right?? So it's now a wave and not a particle?

So I wonder why the gradient in coordniates other than cartesian ones bears coefficients. Let's take spherical coordinates for example. We have (Source) - Sorry if image doesn't work - too lazy to get the TeX right.[/size] From what I know, I don't see anything that raises cartesian...

According to my physics textbook, the equation E^2=\left(mc^2\right)^2+\left(pc\right)^2 suggests that a particle may have energy and momentum even when it has no rest mass, and that the total energy then is E=pc. This strikes me as odd, since the relativistic momentum of a particle is given by...

SOLVED Given initial angular velocity of wheel, find revolutions to rest Homework Statement As a result of friction, the angular speed of a wheel changes with time according to d \vartheta / dt = 4.1e-.088335775t where the initial angular velocity is 4.1 rad/s. Find the number of...

Homework Statement Thanks for everyone that helped me with the physics questions! I had my physics 2 final today and got a 94! There was a question that I could not figure out for a long time. It goes like this. What would the velocity of the photon be if the Kinetic energy of the photon...

I have read over the definition of the derivation of the energy relationship with momentum and rest mass and I am a little confused. By looking at the definition of relativistic mass we have the definition m = m0 / SQR(1 - v^2/c^2) where m0 is the rest mass. Now a photon always travels...

Homework Statement In the figure below, an open tube of length L = 1.8 m and cross-sectional area A = 4.6 cm2 is fixed to the top of a cylindrical barrel of diameter D = 1.2 m and height H = 1.8 m. The barrel and tube are filled with water (to the top of the tube). Calculate the ratio of the...

Hi How would I show that the centre of mass of two point particles, one of mass m1 and the other m2, when released from rest from infinite simultaneously, stays in the same place? I feel this is a very simple question, I just can't seem to get it right. Everything I've tried still involves...

Does the CMB allow special "almost" rest frames to be defined? In this sense, use a rocket to put yourself in a frame of reference such that in this frame observations of the CMB would average to zero (average over photon momentum) over your celestial sphere. In such a rest frame is the total...

http://www.thrfeed.com/2009/03/discovery-universe-hawking.html I'm really excited about this. Planet Earth was such an amazing series that did what a lot of hopefuls failed to do: tap into the sit-com audience. For a lot of us, 'Universe' will just be a cool rehash of things we already know...

From what this layman can comprehend of Einstein's relativity is that mass causes a curvature of space-time. This space-time is a 4-dimensional geometrical construct. An object moving through a gravitational field would deviate from its straight space-like path in order to achieve the closest...

Hi. I am someone who would like to begin to understand the mathematics behind physics. I have forgotten much of the math that I was taught in high-school, not that I paid much attention at the time, unfortunately. I ran across the book The Mathematics of Relativity for the Rest of Us which looks...

Homework Statement Two stationary positive point charges, charge 1 of magnitude 3.45 nC and charge 2 of magnitude 1.85 nC, are separated by a distance of 50.0 cm. An electron is released from rest at the point midway between the two charges, and it moves along the line connecting the two...

Homework Statement What is the rest mass energy of one mole of neutrons? Hint one mole is 6.02 x 10[SIZE="1"]23 particles (avocado's number), and the neutron has mass m=1.675 x 10 [SIZE="1"]-27 kg. Homework Equations The Attempt at a Solution I wasn't sure of the relationship...

Homework Statement Two blocks, A and B (with mass 20.0 kg and 40.0 kg , respectively), are connected by a string, as shown in Figure P5.64. The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between block A and the incline is μk = 0.290. Determine the change...

Is there such a thing as "at rest"? I've been watching some lectures on relativity from a professor at Berkley and he brings up the central idea of the "reference frame" relative to being in motion or "at rest". He says that if I were to ask you if you were currently in motion or at rest...

why do bodies at rest weight more than zero? here is the bull thing... now I am sitting on my chair and i know Earth exerts a force on me which is called my weight. by definition w=mg I DO NOT have any acceleration g or anything else. let me prove a = dv/dt my speed is zero v = 0, coz...

Two MM-devices A and B (=two perpendicular arms x and y being the paths for light signals) are at rest in the same frame. Both arms are of equal length, say, 1 light-second long. B is accelerated away along the positive x-axis and reaches relative velocity, say, 0.5 c. I asked: will B have to...

Homework Statement here's the problem A 68.5 kg skater moving initially at 2.40 m/s on rough horizontal ice comes to rest uniformly in 3.52 s due to friction from the ice. Homework Equations F= ma The Attempt at a Solution I'm sure this equation is reliant on finding the...

Hello all, First off, I am not sure if these questions belong in this category. For a couple of years now I have been interested in physics/quantum mechanics, and a while ago I decided it was probably my main interest. After realizing my school did not offer physics, and therefore not...

In QM, the energy of a particle with a non-zero rest mass is Planck's constant times the frequency. How does the energy associated with the rest mass m0c2 fit into this picture? Planck wrote of an "instrinsic frequency" associated with the rest mass. Thanks in advance.

Homework Statement [This probably seems really easy to the physics whizzes out there but...*blushes*] Two identical cylindrical vessels with their bases at the same level each contain a liquid of density 1.30x103 kg/m3. The area of each base is 4.00cm2, but in one vessel the liquid height is...

Homework Statement Mass of 22kg on a 45o to the horizontal. \mus = 0.78 \muk = 0.65 Determine the magnitude of the largest force that can be applied upward parallel to the ramp to have the box remain at rest. AND Determine the magnitude of the smallest force applied to the top of the box...

Homework Statement A steam engine is running at 200 RPM whe nits steam is shut off. The friction of its various parts produces torques that combine to decelerate the machine at 5.0 rad/s^2. How long will it take to come to rest? Please help asap I have a test tomorrow. Homework...

This is probably a very elementary question so I apologize in advance. Relativity says that objects of great mass warp the fabric space, hence why we experience gravity. Do objects of great mass simply warp and float ABOVE the fabric of space, or do they rest ON the fabric like marbles on...

Homework Statement An object at rest explodes into three pieces of masses 5.00 kg, 10.0 kg and 20.0 kg. The 5.00 kg piece moves west at 30.0 m/s; the 10.0 kg piece moves southwest at 20.0 m/s. What is the velocity of the 20.0 kg piece and what direction is it moving? Homework Equations...

can anyone help me to solve this question? please and thank you :D A small block slides from rest from the top of a fixed frictionless sphere of radius R. Determine the vertical distance traveled by the block, x , where it loses contact with the...

What exactly do we mean by rest energy of a particle ? It is known that electron has rest energy of .511Mev but what is meant by this ? An electron is never at rest (except in its own frame of reference) then why it is said rest energy ?

Please help! i know how to do a elastic collisions in 1 dimension, but the 2D is too confusing...here is my problem: You have a blue ball with a mass of 1.5 kg moving with a speed of 4.5 m/s in a direction below the positive x-axis. You have a red ball with a mass of 3.6 kg moving with a...

Homework Statement For a car starting at velocity=0 m/s, what would limit the acceleration in the first fraction of a second? (It's isn't the power of the engine) Use the fact that the force acceleration the car is the power over the velocity minus the air resistance force. The drag...

This concept would be dependant on having the technology to actually travel at velocities which we can now, only impart to particles Ie: .99c The plan would be to have 3 ships somewhere in space with negligable gravitational effect. 2 of the ships set out in opposite directions...

Homework Statement A moving 2.3kg block collides with a horizontal spring whose spring constant is 258 N/m. The block compresses the spring a maximum distance of 0.09m from its rest position. The coefficient of friction (mu) between the block and the horizontal surface is 0.32. What is the...

Homework Statement A charge q of mass m is released a distance d from a semi-infinite grounded conductor. How long will it take the charge to reach the conductor? So I tried this using the method of images, and I can easily find the force on the charge a distance d away: F = -q^2 zhat /...

Homework Statement So this was part of a two part thing, the first part was just to find out which statements were true and i figured that out but as far as this i just don't know what to do. this first stuff is for the problem that i already have and it is the second stuff that i need the...

Homework Statement A 2.80 kg mass, m, on a frictionless table is moving in a circle with radius 0.440 m at a constant speed. m is attached to a 5.40 kg mass, M, by a cord through a hole in the table. Find the speed with which m must move for M to stay at rest. for this one i am completely...