Questions tagged [relative-motion]

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If the escape velocity for a body that is very close to a BH is near $c$ but not $c$ can it move away a little bit before it falls inside the BH?

The escape velocity from a common gravtational attractor means that a body lounched away from the attractor will never turn back. But in the case of a BH at the event horizon this escape velocity is $...
1 vote
1 answer
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Where does the relative velocity composition law equation come from?

I'm trying to understand this paper (equation $2.8$ specifically): Bini, D., Carini, P., & Jantzen, R. T. ($1995$). Relative observer kinematics in general relativity. Classical and Quantum ...
-2 votes
1 answer
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What is the relative acceleration of a ball thrown inside a bus with respect to a man sitting inside if bus has uniform velocity? [closed]

Like both man and ball are experiencing acceleration due to gravity so will the ball have no acceleration w.r.t to man?
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Is e (COR) defined for whole situation or just during collision

According to wikipedia $${\text{Coefficient of restitution }}(e)={\frac {\left|{\text{Relative velocity after collision}}\right|}{\left|{\text{Relative velocity before collision}}\right|}}$$ ...
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Determine orbital motion of a binary

I consider two objects with masses $M_1$ and $M_2$ in a system. The coordinate system was chosen in such a way that the origin of the coordinates lies in the center of mass. Means: If $\vec{x}_1$ and $...
3 votes
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Wind and sound waves [closed]

The official answer is C. Why not A? If I add a horizontal component of velocity towards left, why would the path become curved?
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1 answer
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Why can't any object gain the speed of light? [duplicate]

Suppose a object A is moving towards left with 200,000 km/s and objects B moving with 200,000km/s towards right. According to this above Statement, this could be happened because Speed of objects is ...
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2 answers
65 views

Velocity of one particle w.r.t. another

Let us say that two particles $p_1$ and $p_2$ are moving in an inertial frame fixed to some point on earth. Call this frame as world frame. The velocity of $p_1$ is $(v_{1x}, v_{1y})$ in $x-y $ ...
0 votes
2 answers
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What angle does a projectile have to be shot on a rotating disk in order to pass through the center?

Let us consider the following setup: We have a rotating disk of radius $r$ and with angular velocity $\omega$. At the periphery of the disk, we have a projectile with some mass that's sent with a ...
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4 votes
5 answers
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Can't understand a statement about motion

From the book where I am studying motion, It says Motion is a combined property of the object under study and the observer. There is no meaning of rest or motion without the viewer. I know that, for ...
1 vote
4 answers
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A problem Understanding how a two-body system of planets starts rotating around barycentre

Consider,We are Creating a Two-body system in free space,Where no other mass exists,Let's Take First Mass M1 and hold it,Now bring Second Mass M2,hold it up,Now we are giving a suddenly impulse To M1 ...
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Minimum seperation of moving objects doubt

Let there be $2$ objects $P_1$(initial velocity $u$ $ms^{-1}$ & acceleration $a$ $ms^{-2}$) & $P_2$ (initial velocity $U$ $ms^{-1}$ & acceleration $A$ $ms^{-2}$) initially separated by ...
-2 votes
1 answer
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How can I calculate the relative velocity on the surface of a planet that is both rotating and orbiting a star? [closed]

So here is the problem that I'm dealing with: I thought that I could just subtract the 10000 m/s from the 30000 m/s since they're spinning opposite of each other but that didn't end up giving me the ...
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1 answer
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Angular velocity of a particle in uniform circular motion about a general point

This problem was given by our professor. Consider a particle P executing uniform circular motion wrt the point O with uniform angular velocity $\omega$ anticlockwise whose cordinate is $(2R,0)$ in a ...
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Is there a bug in this step (and how to fix it?)

Reading an old book of classical mechanics (Spiegel's theoretical mechanics) I came across a passage that I would like to clarify. In order to find the equations of motion of free falling point ...
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3 answers
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Why is the speed of near speed of light moving particles not over the speed of light?

I've been looking for an answer to this question for a while now and I've seen the mathematical explanation $$Vr=[V1+V2]/[1+V1*V2/c²]$$ I understand that the result cannot be greater than $c$ because ...
5 votes
5 answers
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How is a change in KE the same in every inertial reference frame?

This is not about special relativity, so assume speeds are much less than $c$. This article says a change in kinetic energy (KE) remains constant in all inertial reference frames. So the kinetic ...
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1 answer
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Kinetic energy consistency

Suppose a vehicle 1 is on the top of another vehicle 2 (we can think of it like a big platform). Imagine the following independent experiments: Suppose that the top vehicle accelerates to a speed $...
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2 answers
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Average speed / Velocity

We know that in kinematics we have the concepts about "average speed". By definition the average speed is the total of the distance divided by time, but I still don't get it what is the ...
2 votes
2 answers
190 views

Does the speed of sound wave change when the source velocity change?

The speed of sound in air is about $740$ miles per hour. Suppose that a police car is sounding its siren and is driving towards you at $60$ miles per hour. At what speed is the sound of the siren ...
7 votes
6 answers
2k views

Is it wrong to just say that things continue at constant velocity unless acted upon, as velocity is only relative?

Like when saying that people mistakenly thought things automatically slowed down after being thrown etc (accelerated), because that's just due to all the air or surface friction or gravity. Do you ...
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2 votes
3 answers
538 views

If I accelerate through space, can I say all stars gain kinetic energy?

Suppose I accelerate through empty space. Say all stars are small heavy marbles I can use to do work with by means of their velocity. Say I can let them smash into some generator that turns their ...
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3 answers
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What exactly will happen if you jump in the upward direction from a roof of on a moving car?

I'm not a physicist and I'm a little bit puzzled with the image below: I know it's a joke but if we assume we don't have air resistance what exactly will happen if someone jump in the upward ...
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Relative angular velocity and linear acceleration of a fixed rigid body coordinate with respect to another moving rigid body coordinate

Let me describe a problem I currently have: The robot (orange box) moves around the object (green box) located in a fixed position. Odom keeps providing a homogeneous transformation (rotation and ...
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2 answers
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Question about relative motion from "A Brief History of Time" [closed]

I read this example in Stephen Hawking's A Brief History of Time: If one sets aside for a moment the rotation of the Earth and its orbit round the Sun, one could say that the Earth was at rest and ...
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3 answers
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If I'm moving with almost speed of light but without any acceleration will I see any relativistic effects?

As the moving is relative there is no matter on which speed you are moving if there is no acceleration. We will fill it exactly the same as no moving (if other objects moves with the same speed). So, ...
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2 votes
2 answers
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Confusion regarding Inelastic Collisions contradicting my book

Suppose two bodies $A$ and $B$ with equal mass are kept at a distance. $A$ starts moving towards $B$ at a constant velocity, they hit, and I assume that it is a PERFECTLY INELASTIC collision here. ...
1 vote
1 answer
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Linearly Interpolating in a Non-Inertial Frame

I am working on an engineering task where we have a flying object which knows its height above a curved surface as well as how close it is to other flying objects. If I want to interpolate between two ...
5 votes
3 answers
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What is the "true" distance an object travels based on relative speeds?

There are two objects (x and y) with x travelling at 10km/h and y travelling at 11km/h, both with respect to the earth. After 1h, from the perspective of the earth, y travels 11km, but from the ...
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Is there any physical experiment that could tell us which object is moving to the other?

Imagine in empty space there are two objects in where one of them is moving to the other. How we can know which one is moving to the other? If there is an experiment that could tell us, would this ...
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0 votes
3 answers
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How can an accelerated frame and a gravitational field be equal?

How can two things that are different be equal? In a gravitational field there is actually gravity that push us down, but in the accelerated frame there is nothing that push us down.
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3 votes
3 answers
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Relative velocity related to acceleration

Let's say we have a car moving on the horizontal ground with a velocity of $10 \hat{i} \frac{m}{s}$. A person inside throws a ball vertically upward with a velocity of $3 \hat{j} \frac{m}{s}$. Now I ...
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3 answers
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A question about relative motion and how to make sense of it

So, here is the question: Assuming the 2D Cartesian system and the basis vectors $\hat{i}$ and $\hat{j}$, we have two cars A and B located at (0,6) and (-30,0) respectively. Car A starts moving with a ...
1 vote
5 answers
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Thought experiment on relative motion

Imagine two persons (A and B) in a vacuum in outer space that are in front of each other and are not in motion. Say that suddenly A starts moving away with a constant velocity from B. In this case, ...
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2 answers
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Why is light speed constant even in respect of a moving body? [duplicate]

My teacher told that speed of light is constant. The speed of moving object appears 0 when seen by another moving object( of same speed as that of first) but she told that light speed is constant ...
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2 answers
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Sign convention for relative displacment

If an object A is $X\ \mathrm m$ behind B,than the relative displacemnt of A wrt B would be $-X$. However is object A was moving towards B(at rest) at a rate of $Y\ \mathrm{m/s}$, then $$V_{ab}=+Y-0=+...
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3 answers
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Kinetic energy "paradox" -- where am I wrong here? [duplicate]

Body $A$ is at rest and has mass $2$, so the energy required in order to accelerate it to a speed of $v$ is $v^2$, and so the energy required in order to accelerate it to a speed of $2$ is $4$. On the ...
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1 answer
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For an airplane moving north from some latitude (say $30^{\circ}N$), why does rotation of the Earth cause an increase in apparent drag?

I'm not able to understand the answer to this example: Example 10 from the Curtis Orbital Mechanics text book : An airplane of mass $70 000\ \mathrm{ kg}$ is traveling due north at latitude $30^\circ$...
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11 answers
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What is the essential difference between constant speed and acceleration?

I do know what the difference is but what I am trying to understand is how an object knows its speed is changing and/or how space knows an object is accelerating. The particular thing I am interested ...
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How do you find relative motion of two objects not travelling in a straight path?

I understand relative motion linearly, but how about more complex motion, like travelling in a circle? Would you just find the objects velocities at some point using the formula $v=\omega r$ and then ...
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Relativistic addition of velocities

Suppose I have two frames of reference $S$ and $S'$ moving relative to each other. Suppose an object has a velocity of $v_s = a\hat{i}+b\hat{j}\space$ in the frame $S$. Similarly, it has a velocity of ...
2 votes
5 answers
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If motion relative to a frame of reference is purely relative, how do we account for the work done to move relative to the frame of reference?

I get the idea that everything is in motion, and there's no absolute reference frame for everything. But when we consider local events, like a train passing through a town, I have trouble accepting ...
9 votes
3 answers
834 views

Greatest distance between a particle moving with constant velocity and a particle moving with constant acceleration

Two particles start moving along the same straight line starting at the same moment from the same point in the same direction. The first moves with constant velocity $u$ and the second with constant ...
0 votes
2 answers
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How do we know if a particle is moving or not? [duplicate]

if there is only one particle in the universe, how do we know if it is moving or not? We don't have any other object to track the distance between the two, then is it possible to determine the ...
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1 answer
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Does the rotation of Earth make two electrostatically charged bodies interact magnetically (with each other)?

Does the rotation of Earth make two electrostaticaly charged bodies fixed on its surface interact magnetically (with each other)? If yes, is this interaction different as geographical latitude changes?...
2 votes
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Should the velocity increase or decrease?

Suppose some projectile is traveling along the positive $x$ direction at a velocity $v$. While moving it is emitting particles, and thus losing mass. If the particles are being emitted in the same ...
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0 answers
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Doubt regarding derivation of rocket equation

I'm having quite some issues deriving the ideal rocket equation, and I suspect it is due to lack of identifying scalar terms and vector terms. Here is how I derive it : Let $v$ be the velocity of the ...
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1 answer
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Can a bubble of vacuum move through space?

If there are really regions in space where a vacuum exists, I have learned there can still exist electric and magnetic fields within. That makes this region then differentiable from the regions around ...
16 votes
10 answers
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Why do bodies traveling at constant velocity experience the same physics?

I am new to special relativity. I don't have a background in physics. I was reading Brian Green's The Elegant Universe and got hung up on an example. In fact, Einstein realized that the principle of ...
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1 answer
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Distance between two airplanes [closed]

I need help with a vector problem where my solution is different from that of my teacher. The translation of the problem reads as follows: An air traffic controller observes two aircraft on his radar ...

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