The time rate of change of the position of an object

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How are the theoretical properties of a gravity train linked to orbital properties?

Whilst perusing a question on WorldBuilding, a link was given to an article about Gravity Trains. Some of the answers on the question, and the Wikipedia article, state a travel time of 42 minutes ...
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1answer
5k views

Calculating time to reach certain velocity with drag force

I was given a problem for homework where we needed to calculate the time for a falling object to reach a certain velocity when accounting for drag force. I did it by setting up acceleration as a ...
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1answer
427 views

Does decreasing the length of the line between a harness and zip wire increase the velocity at which you travel?

My friend is an instructor at an outdoor adventure centre which has lots of zip wires. The instructor's harness has a shorter line that attaches to the zip wire than the normal harness does and she ...
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1answer
620 views

How do I find the initial velocity in this problem?

An X-ray tube gives electrons constant acceleration over a distance of $20\text{ cm}$. If their final speed is $2.0\times 10^7\text{ m/s}$, what are the electrons' acceleration? I know this equation ...
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1answer
69 views

Can a “flat function” be a particle trajectory? [duplicate]

Recently I came across the concept of a flat function, which is a smooth function $f:\mathbb{R}\to\mathbb{R}$ all of whose derivatives vanish at a given point $x_0\in\mathbb{R}$, the canonical example ...
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0answers
456 views

Finding the terminal velocity of a magnet dropped in a solenoid

We have to find proportionality of the terminal velocity with the factors of the system: Plot: a small dipole(mass $m$) with dipole moment $\mu$ is dropped in a long solenoid (radius $r$, ...
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2answers
242 views

Air velocity in a double-skin facade

I was wondering how the air flows in a double skin facade? Say I have a glass facade with a depth of 1m, a height of 200m and a width of 10m. It is a single vertical shaft all the way up with openings ...
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3answers
561 views

Basic question about acceleration [duplicate]

Very basic question. Please show where I'm wrong in the following reasoning. The movement of an object in function of time could be described as $$ x(t) = v t + x_{i} $$ if velocity is constant. If ...
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3answers
362 views

A question in Special Relativity

In books the equation for length contraction is derived by supposing that the velocity of the spacecraft is the same for both observers. So the question is that, is the velocity really the same for ...
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3answers
24k views

What is the difference between angular speed and tangential speed in a circular motion?

I was looking a long time for the way the equations of this two speeds are obtained, and i found pretty much nothing important, so can someone explain how are those obtained, and which is the ...
2
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2answers
757 views

Does light have initial velocity? [duplicate]

You are standing still in a vacuum, and you throw a ball that moves 10 m/s away from you. Now you start moving in one direction at 5 m/s, and throw the ball in the other direction, away from the ...
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2answers
782 views

If gravitation causes constant acceleration why moon does not fall into earth? [duplicate]

If moon travels with constant speed in one direction and earth gravitation causes constant acceleration in perpendicular direction why moon does not eventually fall into earth? I mean if gravitation ...
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4answers
317 views

Are circularly defined {velocity, distance, and time} a problem in physics?

In order to measure velocity, one needs a calibrated measuring stick and clock. But in order to calibrate a measuring stick you need a calibrated clock and velocity. And in order to calibrate a clock ...
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2answers
183 views

Thought experiment that seems to involve something growing at twice the speed of light. Is anything wrong?

Let foo be some unit of distance and bar be some unit of time which have been chosen so that the speed of light c = 1 foo/bar. Position several observers along a line each separated by one foo, and ...
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1answer
130 views

Measuring more accurately the distance of remote galaxies

From what I read in Wikipedia, the velocity of a Galaxy has two components: one is due to Hubble's law for cosmic expansion, and the other is the peculiar velocity of the galaxy. Since the peculiar ...
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1answer
404 views

Isn't the front edge of a wave, kind of “information” which travels faster than light?

Considering the definition of phase and group velocities, We know group velocity can't exceed C but phase velocity can be infinitely high. Assume a monochromatic electromagnetic wave traveling with a ...
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3answers
2k views

What is the velocity area method for estimating the flow of water?

Can anyone explain to me what the Velocity Area method for measuring river or water flow is? My guess is that the product of the cross sectional area and the velocity of water flowing in a pipe is ...
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1answer
461 views

whats the rate of energy increase required for constant acceleration between 0.0c and 0.99c?

I was wondering how much energy would be required to accelerate 1000kg to 0.99c at 1G. What I don't understand is what the rate of increase of energy is required as velocity increases. I was looking ...
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2answers
303 views

How do you travel in a circular orbit around a massive body?

I am trying to figure out how an object could achieve a perfectly circular orbit. Given a mass for the planet or other body the object is orbiting and a distance from the center of mass, how fast ...
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3answers
874 views

Train crash: are these situations alike? [duplicate]

I was just wondering... I believe that if a car travelling 50 miles per hour crashes into a wall, the result should be the same as crashing to another car also travelling 50 miles per hour (but in the ...
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1answer
208 views

Visualisation of electron

first things first, I'm not by any means a physicist nor a student of physics. I study graphic design. Theme of my bachelor thesis is visualisation of physical and mathematical phenomenons, long story ...
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3answers
1k views

Does mass affect velocity when travelling through frictionless medium?

I found the following question on an standardized test, and was debating with some friends what the answer would be: A car of mass M is travelling with a constant velocity through a plane in which ...
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3answers
451 views

Velocity measurement in relativistic perspectives

I understand the precepts of relativistic time dilation, but I'm looking to nail down the local perception of velocity in each frame. My question is threefold: Given two observers $A$ (rest frame) ...
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1answer
618 views

Where do the equations for resistive force come from?

I've been watching MIT's Walter Lewin physics lectures. In lecture 12, Lewin pulls, out of nowhere, a couple of equations regarding resistive/drag forces in fluids: $$\begin{align} \vec{F_{res}} &...
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2answers
429 views

Mathematical model for this graph of a simplified binary star system?

Unnecessary background for question: I had a school assignment asking us to relate a quadratic equation to a real life example relating to our future dream career, making sure to express the accuracy ...
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3answers
532 views

If you could reverse gravity, what velocity would you achieve on leaving Earth?

If you could reverse gravity, to make it repulsive instead of attractive, what velocity would you achieve on leaving Earth? A simple question really, but I have completely forgot how to calculate ...
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1answer
179 views

Motion is relative, right? And most pop sci relativity explanations are somewhat incorrect?

On page 20 of A Brief History of Time: . . . all observers should measure the same speed of light, no matter how fast they are moving. But in an observer's frame of reference, they're actually ...
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1answer
588 views

Concept of relative speed

I am traveling on a train running at a speed of 100mph. If from the train I shoot a ball at a speed of 100mph in opposite direction then what would be the speed of the ball with respect to a person ...
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2answers
45 views

Juno probe's speed is in relation to what frame of reference?

When describing the velocity of space probes in general (the Juno probe in particular) what frame of reference is the velocity quoted in? This is in relation to the news of the Juno Satellite ...
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1answer
52 views

Why is the potential independent of the generalized velocity?

In Goldstein, Classical Mechanics, Chap. 1.4 we derive Lagrange's equations from D'Alembert's Principle. My question is regarding the last part of the derivation, specifically the part where he ...
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2answers
125 views

What is meant by the velocity of a star?

I recently read somewhere that among other things like size, radius, distance from earth, luminosity, age, etc of a star, velocity was another variable. What is exactly meant by the velocity of a star?...
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2answers
2k views

If two objects have all the same conditions except different masses. Will their terminal velocity be different?

I can't seem to find a straight forward answer to this. I really just want to know if changing mass of an object affects the terminal velocity. If two objects of the same dimensions except one had ...
2
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1answer
709 views

Calculating the eccentricity of an exoplanet

I'm wondering how to calculate the eccentricity of an exoplanet by its radial velocity vs. phase graph. To clarify my question I will take an exoplanet called WASP-14b 2 as an example (http://...
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2answers
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Factors on which Coefficient of restitution depend

What are the factors on which coefficient of restitution depend? What is the reason for more coefficient of restitution of two glass balls (0.95) than for two lead balls (0.20)?
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1answer
77 views

Change in velocity of a circular orbit?

For a body in a circular orbit will any (i.e. however small) decrease in velocity mean it falls to earth or will it go into an elliptical orbit? I originally thought that it was the first (i.e. falls ...
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2answers
1k views

What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere?

What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere? the comet is falling radially towards the earth. Will this velocity be ...
2
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1answer
307 views

Determine orbital position after change in velocity

I am working on a satellite simulator for a project/game and I am stuck on this one bit of physics. So far I have a satellite that revolves around earth on a 2D plane following Keplerian motion using ...
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1answer
227 views

Speed of three objects falling with different masses

The following is the problem that I am working on. Three different objects each with mass $m_1<m_2<m_3$ is launched from the same height $h$ with three different angles $\theta_1 < \...
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2answers
434 views

Understanding units manipulation (speed of falling coconut after 20m)

When I was on holidays, I was told a story about how someone passing under a palmtree and almost got a coconut fall on his head. Given that these palmtrees where about $20m$ high, we wondered at what ...
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1answer
4k views

Kinematics with non constant acceleration

A particle experiences an acceleration described by $$ a=kx^{-2} $$ where x is the displacement from the origin and k is an arbitrary constant. To what value does the velocity v of the particle ...
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1answer
56 views

Difference between escape velocity and speed [duplicate]

What is the difference between escape velocity and escape speed , is their any error if we use them interchangeably?
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2answers
123 views

Velocity addition rule in special relativity

I just worked out a problem showing peculiarities of the velocity addition rule in special relativity. This was the statement for the problem: "Nefarious thieves flee the scene of their bank ...
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3answers
2k views

How to figure out the height it would take for an object to reach terminal velocity?

I'm trying to figure out how high an object would have to be dropped to reach it's terminal velocity. Specifically if an object had a terminal velocity of 520 mph, how would I figure out how high it ...
2
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2answers
120 views

Sum according to a function - composition of velocities

An observation more than a question. Take any function $f$ (additional hypotheses may follow) and evaluate it on any two points $x_1, x_2\in\mathcal{D}_f$. Define then the sum of these two points as ...
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4answers
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Are wavelength and the distance same thing?

Can you clarify for me the following question: are wavelength and distance same? I know wavelength is measured in terms of distance but when we have a look at the two equations: $$ c=f\,\lambda\\ ...
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2answers
2k views

Velocity of car down an Inclined Plane

I was learning to make a car game and came across this situation where my car is on an inclined plane. It's initial velocity is 0. Now, the problem is that my memory serves me this formula to ...
2
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1answer
2k views

Drift velocity of electrons with changing area

What would happen with the drift velocity of a cylindrical resistor's diameter increases, with a given voltage between its terminals? According to the expression: \begin{align} R&=\rho\frac{L}{A}\...
2
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2answers
525 views

Elastic collisions and conservation of momentum

If you have an elastic collision between objects 1 and 2 and where 'kinetic energy is conserved', does this mean object 1 will always have the same velocity it had before the collision? Or will ...
2
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1answer
745 views

How to find equation of motion for this trajectory? - object leaves curved ramp at a given velocity [closed]

Here is the sketch: The sketch is supposed to be side-view of the path of the object. The following values are known: $r$ - radius of the circle that describes the path AB of the object $a$ - ...
2
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1answer
84 views

Is it possible to affect the trajectory of a black hole?

Basically is the black hole itself affected by the matter going into it? Does it either get pulled by gravity toward things or have its own velocity affected by matter that "impacts" it?