Speed Definition and 999 Threads

This problem bothered me many years ago when I was taking a university course in quantum mechanics, but I assumed it was due to an error on my part which I, however, couldn’t locate, and I didn’t ask my course instructor about it. Recently, when researching a q.m. question on the Internet...

The two spaceships A and B approach each other at constant speed v: A----------B There is no way of knowing if B is standing still while A is moving at speed v (to the right), or if A is standing still while B is moving at speed -v (to the left). This shows that speed is relative. But if the...

In school, I was taught that the position of an electron relative to the nucleus is only an approximation. It is very likely that the electron will be close to the nucleus and where it is 'expected' to be, but it may in fact be anywhere in the universe. Is this correct? And does this allow...

So I followed the derivation of the Macroscopic Maxwell's equations by averaging the fields / equations and doing a taylor series to separate the induced charges and currents from the free ones. But why does light now "suddenly" travel slower in dielectric media? I mean, sure, it comes out from...

At supersonic speed, air become compressible. However why does Mach number decrease when flow area decrease? I understand that pressure will increase because the density will increase when flow area decrease. However shouldn't the Mach number increase in order to conserve mass flow? Unless the...

Sorry, me again. In another thread #47 I gave a experimental setup to detect an anisotropy in light speed of the form ##c(\hat{n}) = c_o + \alpha (\hat{n}\cdot\hat{v})##. It was pointed out quite correctly that the error incurred in the long arm to the sensor would cancel the anisotropy making...

Homework Statement I am having difficulty understanding the conversion between power and rotation at the engine and at the wheel. Can you please state which parts are right and wrong, and why please as I think I've spent that long on researching I've confused myself with too much information...

Has anyone encountered the term "hypersonic sound speed" in connection with fluctuations of thermodynamic quantities in condensed matter? How is hypersonic different than regular sound?

Is there any relationship between the Speed of gravitational waves and the Universe's "local" expansion rate? Speed of gravitational waves is supposed to be equal to the speed of light. Gravitational waves don't travel faster than light. But we can observe far galaxies moving away from us with...

Homework Statement Homework Equations [/B] Equations of motion: v = u + at s = 1/2 (u + v) t s = ut + 1/2at^2 v^2 = u^2 + 2as 3. The Attempt at a Solution Hello, on a i used the 2nd equation: 30m = 1/2 (3*10^8m/s+3*10^8m/s) t so -> t = 1*10^-7s but to get the correct solution i...

$\text{A person jogs eight complete laps around a $400 \, m$ track in a total time of $14.5 \, min$}. \\$ $\textit{a. Calculate the average speed in $km/h$}\\$ \begin{align*}\displaystyle \frac{(8)400 \, m}{14.5 \, min} \left(\frac{km}{1000m} \right) \left(\frac{60 \, min}{h}...

Hi, What is people measuring when they measure the speed of light (c) actually? the photons or the waves? or some kind of manifestation of light? I ask because I was reading about photons and that they "might" have a very small mass and therefore are not traveling at c. If photons have a...

Homework Statement Homework Equations E = γmc2 p = γmv K = E - mc2 E2 = c2p2 + m2c4 The Attempt at a Solution I have completed most of this question, but I am struggling to get the required result to the final part of the question.[/B]

Good morning. I've just completed working through Einstein's work on special and general relativity. Do I understand that, in relativity, a moving object cannot measure its own speed without an external reference to compare to? IE, there is no experiment it can conduct to determine its own...

Homework Statement Homework EquationsThe Attempt at a Solution When the source is not moving, ## \lambda = 6250 A ## ...(1) When the source is moving, ## \lambda ' = 6500 A ## ...(2) From (1) and (2), ## \lambda ' > \lambda ## ...(3) This means that the source is moving away from...

1.Why does the angular speed of small gear depend only on larger gear only? 2.Why does the length of linkage connecting two gears does not have any influence on the angular speed of smaller gear? The first question can be answered by looking at slack and tightening of chain caused by rotation...

A cart which weighs 500g is moving on a horizontal table with the starting speed of 7 m/s. At the end of the cart there's a non-elastic wire attached, which is thrown over a pulley, and on the other end of the wire there's a 200g load. I need to find the speed of the cart and the distance it...

I have two pressure vessels (volumes known) at different pressures (known) . There is a connecting tube between them of known diameter. I first want to calculate velocity during the equalization and should easily be able to determine the time to equalization. P1 V1 P2 V2 Cross section of...

I've learned that ideal gases have the same average kinetic energy, but this doesn't necessarily mean that they have the same speeds within a container..Instead, is it right to say that (according to kinetic molecular theory) that the speed of molecules at an instance is a wide range of speeds?

If the speed of light is ~300 m/s in a vacuum, can the electric and magnetic fields of the wave be condensed such that it travels faster? The idea being that an outside force condenses these fields and lenghtens the wavelenght with no loss of energy thus increasing the directional speed. The...

Homework Statement If the car is going 30 m/s half way up the loop and loses energy due to friction at a rate of 2.0J per meter of track, how fast will it be going at the top? (this is question related to the loop of roller coaster track, with radius 20m.) Homework Equations 1. Ki + Ui = Kf +...

Why the speed of light is constant for every observer ? Is it a special thing for photons cause I guess there's no other elementry particle that can move with c ? Also I want to investigate the constant of c for every observer, in the perspective of particle relationship. For example, can I...

Hi there, so I want to know how to get the speed I need to move some object from point A to B, accordint to the distance between points, gravity and height angle. I means, I have this: height angle = 40.0 distance from point A to B = 5m gravity = -9.81 speed = ? I think that I just need to know...

Homework Statement An object of mass 100kg is acted on by a constant force as it moves through a displacement at a constant speed of 7.2m/s. What is the net work done on the object? Homework Equations Wnet = ΔK Fnet = 0 The Attempt at a Solution I know that the answer is zero because the...

Homework Statement 14.11 A boy slides down a water chute, starting from rest a A. Neglecting friction determine his speed (a) at the end B of the chute; and (b) on entering the water at C. Homework EquationsThe Attempt at a Solution for (a): for (b): Do I have to treat the boy at B as...

Hello, so i know in a free fall the acceleration is constant (9.8 m/s2) therefore speed/velocity is increasing.. But I am wondering why we can't use Speed=D/T

Homework Statement The lawn tractor in figure 18 goes up a hill at a constant velocity. Calculate the power that is developed by the tractor. Mass: 120.0 kg Angle of incline: 21 degrees Distance: 12.0 m Velocity: no velocity given other than it is constant Time: idk Homework Equations None...

Homework Statement The question and the known/given variables are on the image in part 3. The question says that a 20-g bead is attached to a light 120 cm-long string. Now in my mind the bead will travel in a circular path if it is pushed really hard. So Isn't the length of the string, 120 cm...

Homework Statement The exercise is this: The mass of the car is m=500 kg. The maximum speed of the car on flat road is v1=35 m/s and on 10 % up hill (tan(alpha)=0.1, alpha is with respect to flat) the maximum speed is v2=20 m/s. The friction force is double on up hill because it has been made...

Homework Statement What is the escape speed of an electron launched from the surface of a 1.0-cm-diameter glass sphere that has been charged to 10nC? Homework Equations Given: d= 1.0cm r= 0.05cm= 0.0005m q1 = 10nC = 10 x 10-9 (sphere) q2 = -1.6 x 10-19 (electron) Equation: U = (kq1q2)/r KE=...

Homework Statement A proton is released from rest at the positive plate of a parallel plate capacitor. It crosses the capacitor and reaches the negative plate with a speed of 50,000 m/s. What will be the final speed of an electron released from rest at the negative plate? Homework Equations...

Homework Statement A small but very powerful bar magnet falls from rest under gravity through the center of a horizontal ring of conducting wire, as shown in the figure below (on the left). The speed-versus-time graph, in arbitrary units, of the magnet will correspond most closely to which of...

Does centrifugal force generate in increase in overall speed? For example, if I am driving down a highway on-ramp which goes in a circular fashion, with my speed slowly increasing, does my overall speed increase because of the centrifugal force generated from the circular on-ramp? Is more force...

$\tiny{243.13.01.19}$ $\textsf{The following equations each describe the motion of a particle.}$ $\textsf{ For which path is the particle's speed constant?}$ \begin{align*} \displaystyle R_1(t)&= t^7\textbf{i}+t^4\textbf{j}\\ R_2(t)&= \cos(3t)\textbf{i}+\sin(8t)\textbf{j}\\ R_3(t)&=...

We are using VR technology for people with spinal cord injury ( incomplete so they can walk with assistance) for a study. They will be walking on a treadmill wearing an oculus. We have a question regarding relative speed since we are updating the software view based on that if person A runs at 5...

Homework Statement The spring in the figure (Figure 1) is compressed by length Δx. It launches the block across a frictionless surface with speed v0. The two springs in the figure (Figure 2) are identical to the spring of figure 1. They are compressed by the same length Δx and used to launch...

Homework Statement The question is as follows: A 50kg ice skater is gliding along the ice, heading due north at 4.0m/s. The ice has a small coefficient of static friction, to prevent the skater from slipping sideways, but kinetic friction =0. Suddenly, a wind from the northeast exerts a force...

Hello! I have been brushing up my Rigid Body Dynamics. I tried computing the angular speed with respect the Center of Mass (CM) using the usual split of kinetic energy and also the split of Angular momentum using the CM. First, a simple case: Two particles of mass M each separated by a distance...

Can anyone help me with a very basic question please. Is it really not possible for anything to travel faster than the speed of light, as dictated by relativity theory ? I am a complete beginner to Physics and only have very basic mathematics knowledge and I'm trying to understand the basics of...

This is something I haven't been able to wrap my head around yet. In physics, I've always been told that gravity is a force that ALWAYS works between "objects" with mass. Now, it seems clear to me that if a feather and a hammer were to be dropped at the same time on Earth (without air...

So I was wondering that why does time move slower the faster you get ? And does it happen at all or is this is just fake ?

I'm working on some decorative items made of copper. I'd like to have them achieve the brown color of an old copper penny (or the old copper pipes in my home). I've read you can do this with some chemicals, but due to size/shape I'd like to do this some other way. I'm also concerned that any...

Homework Statement This is an example problem I found on khan academy and it didn't have an official problem statement... So I am going to have to make up my own problem statement from what was given. I can link the video if any of you want to see it. A positive charge 4uC and a negative...

Say a super fast car is going car is going at twice the speed of sound, an there is an aircraft going at the same speed. Normally, maneuvering and controlling at high speeds (slowing down, speeding up, stopping and changing direction) is very hard. Now, I just want to make sure by asking, what...

[FONT=verdana]Dear Everybody, How to get started for this problem? An Earth satellite has its apogee at [FONT=verdana]2,400[FONT=verdana] km above the surface of Earth and perigee at [FONT=verdana]750 km[FONT=verdana] above the surface of Earth. At apogee its speed is [FONT=verdana]6,800...

Earlier today, when I saw that Firefox was installing an update when I fired it up, I did my usual groaning facepalm and wondered what I might find broken this time. I've been a faithful Firefox user since 2004, shortly after it appeared on the market. But in recent years, my loyalty has been...

I may have a fundamental misunderstanding of the concept, but I was wondering, how does the accelerating expansion of the universe calculate for the time dilation in light travel? From my understanding, we know that the universe expansion is accelerating because the farthest galaxies that we...

If two clocks start from the same point, and one travels double the speed of another, will they be showing the same time when they get together at the destination point. Obviously, faster clock will arrive first, and will have to wait for the slower one to arrive.

Hello, I have been looking at physics calculators, but cannot seem to find precisely what I need. I don't need a very precise answer, merely a realistic ballpark one. I need to know how we find the rough speed of an object's movement when a certain amount of force is applied to it. For...

Homework Statement The power driving the railroad engine is switched off. The engine stops, from its speed of 16m/s^-1, without braking in a distance of 1.1km. A student hypothesis that the horizontal resistive force is constant. Based on the hypothesis, calculate the mass of the railway...