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Questions tagged [velocity]

The time rate of change of the position of an object

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How can the velocity of elecrons in graphene be measured?

I'm trying to understand how one can measure the velocity of electrons in graphene, from an experimental point of view. Does anyone have some clue?
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physics,finding result by transforming equations [on hold]

The football ball m=1kg was kicked up vertically with speed v=30m/s. Make the model of movement track, also the graph of speed, knowing that Fr=bv2 , b=1 N/m2
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Pressure in the pipe when the pool is draining out

I have a question: the situation is as follows: There is an open pool (in blue) to which a pipe is connected. The pressure above the pool is equal to the air pressure = 1 bar. In normal configuration ...
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1answer
82 views

Relativistic mass effect

Does relativistic mass phenomena only appear while accelerating or even when the object is travelling at constant velocity (say 90% speed of light)?
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Meaning of the term speed of light in context of an object of non-zero mass

We know from GR that an object of non-zero mass cannot propagate at light. I have a problem with the term speed of light. Does it mean the relative speed of that object with another object or frame of ...
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1answer
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Motion of a particle in a uniform magnetic field [on hold]

The questition states: A uniform magnetic field exists given by $\mathbf B=b\ \hat k$ . A particle of mass $m$ and charge $q$ is present in magnetic field has an initial velocity $\mathbf v=v\ (\...
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9answers
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The instant an accelerating object has zero speed, is it speeding up, slowing down, or neither?

This problem is from Khan Academy. Specifically for the blue point circled in red, the answer is that at this blue point, the object is neither speeding up nor slowing down. When I think about the ...
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If absolute velocity does not exist, how can we say a rocket accelerates in empty space?

If a rocket in space fires its thrusters, it is propelled forwards as per the laws of motion. This can be measured by its position relative to other bodies in the universe. Hypothetically if there ...
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How does velocity vary in varying force systems? [closed]

Gravitational and electrostatic forces vary as inversely proportional to the square of the distance. When the bodies in question face attraction or repulsion, the distance changes, and hence the force ...
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Intuition of Distance covered when accelerating [duplicate]

When you're moving at $5$ m/s for $1$ second, you have traveled $5$ m. When you're moving at $5$ m/s (initial velocity) and you accelerate $2$ m/s for $1$ second, you have traveled $5$ m + $1$ m (...
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1answer
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Motion Along a Straight Line: Calculate velocity of a stream

A swimmers speed along the river is 20 km/h and upstream is 8 km/h. Calculate the velocity of the stream and the swimmers possible speed in still water. I understand what the variables are and I ...
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1answer
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How to know is four-velocity is directed towards future or towards past?

Consider a four-velocity vector $\mathrm{u}=(u^0,u^1,u^2,u^3)$. The zeroth component of position is $x^0=ct$. How do I know if $\mathrm{u}$ is directed towards the future or towards the past? Is it ...
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1answer
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High velocity mushrooms?

So y’all know meteoroites burn up in our atmosphere I’m looking for an equation or something that will allow me to calculate how fast a substance can move before it starts to burn up. Specifically I’m ...
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1answer
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Maximum Vertical Velocity of Pendulum

Say there is a 10N pendulum held parallel to the ground. In a frictionless environment, it will continue swinging along a semicircular path. The pendulum tip should have the highest horizontal ...
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5answers
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Intuition of 2D Velocity Vectors [duplicate]

I understand 2D vectors in terms of displacement. For example, Bob moves 3m to the east and 4m to the north, the total change in position (displacement) equals 5m to the north east. But I don't ...
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What is rate of heat produced in terms of radius $r$ in viscous liquid under gravity?

what is the dependency of the rate of heat produced in terms of radius $r$ after the drop attains terminal velocity when A small ball of radius $r$ is falling in a viscous liquid under gravity? My ...
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3answers
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Kinetic energy of an object

We know that motion is relative. So let an object(o) be moving with a certain velocity with respect to an object (A).If another object (B) is moving with respect to (A) at a given moment and they ...
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Observer on rotating ring problem

Assume that there is a ring, This ring is revolving such that its tangential speed, relative to an inertial frame of reference, is near to the speed of light. An observer stands at rest relative to a ...
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3answers
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What is the net force on an object which is moving with a constant velocity? [closed]

Imagine a toy car moving with a constant velocity. By Newton's second law of motion we can see that $F=ma$ and, since there is no acceleration, the net force is zero. But still we can experience a ...
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1answer
48 views

Can I calculate force in the following situation if the following information are given?

A moving car collides with a stationary car, after which they move at the same velocity. After going some distance they stop. The following information is given: mass of the 2 cars the velocity of ...
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2answers
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How does the orbital radius affects the orbital velocity

I have a question says that "If the orbital radius of a satellite increase four times the orbital velocity will be ..." and the answer is that the velocity will be doubled !! We studied that orbital ...
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3answers
50 views

Sign conventions for relative velocity problems

I am having trouble solving relative velocity problems because I can't seem to understand the sign that goes along with the velocity of different objects. $$ v_{ac} =v_{ab} + v_{bc}. $$ How do the ...
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4answers
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What does a negative acceleration mean? Is the object slowing down, changing direction, or both?

I am confused about such things as negative velocity, acceleration, and displacement and what the negative indicates.
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How do you calculate the speed of air when it fills a vacuum of 1 cm³?

At different heights, atmospheric pressure is different. If a vacuum was created of say 1 cm³, how would i calculate the velocity of air filling it back in. The adjacent layer of air would obviously ...
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4answers
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What is the correct formula for relative velocity?

I have consulted byjus.com, HC Verma and Khan academy, all are saying different. byjus and HC Verma book is saying that formula for relative velocity is $V_a +V_b$ but in Khan academy they are telling ...
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2answers
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A beginner's question on time dilation [closed]

I have just started understanding relativity so the question might look absurd. I know that the faster we move through space , the slower we move through time. But I haven't understood it fully. I ...
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2answers
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Is motion smooth? [duplicate]

It's obvious that for every particle velocity is smooth i.e it cannot undergo sudden finite change in its position in infinitisiminal time. Similarly any particle's velocity cannot undergo a change ...
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1answer
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Radial component of velocity at extreme distances

Suppose I am given that a planet's position with respect to some star is of the form $\textbf{r} = r\textbf{e}_{r}$. Then of course $\textbf{v} = \dot{r}\textbf{e}_{r} + r\dot{\theta}\textbf{e}_{\...
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1answer
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How do u get Eq3 from Eq2&Eq1 [closed]

I keep getting the wrong results by subbing eq1 into eq2 It’s from Kleppner’s an introduction to mechanics 2nd edition
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3answers
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What does it really mean by “faster flow, lower pressure”?

My primary school physics textbook trys to brainwash me with the idea that a region in a fluid with fast velocity (often) has lower pressure than a region that flows slowly. Examples of this include ...
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3answers
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Four-velocity vector of light

Please note that my question is not a duplicate, it is not about the speed of light, my question is only technical about the four velocity vector for light, its definedeness, value and constantness. ...
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Choosing motor speeds for an omnidirectional robot given desired linear and angular velocity

Below is an example of an "omnidirectional robot" with four wheels. Each wheel has rollers on it so it can only exert a force along the line parallel to its face, coincident to the ground, and ...
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2answers
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Do objects move in 2 directions at once?

If a velocity vector of an object can be divided into an x and y component relative to a second object's position, and both objects have gravity that attracts both objects to each other. We then know ...
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1answer
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Finding tangential and normal velocity from a curve [closed]

How do you find tangential and normal velocity from a curve? I know how to find dy/dx, but I have no idea how to obtain ut and un and dv/dt.
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4answers
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Does $j=\rho v$ hold in quantum mechanics?

Let's consider the current of probablity $\vec{J}(\vec{x},t)$ associated to a particle of mass $m$ with wave function $\psi(\vec{x},t)$, given by $$\vec{J}(\vec{x},t)=\frac{i\hbar}{2m}(\psi \nabla\...
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2answers
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Do faster moving projectiles make larger penetration holes? [closed]

When it comes to shooting guns, a bullet of a certain size will make a certain size hole in the paper or wood target. A $.22$ bullet makes a pea size hole regardless of if its shot out of a pistol ...
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1answer
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Projectiles with unequal initial velocities, purely horizontal

If projectiles $A$ and $B$ are projected horizontally with different initial velocity from the same height, then both $A$ and $B$ possess the same vertical component of velocity, at any instant. ...
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1answer
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How two cars are getting at the same point of the road (obstacle, cyclist, another car parked on a small part of the road) in the same time? [closed]

You have an ordinary road, two ways. You are driving on the right part of the road and you see a person walking on the same part 400m away, you have to slow down or to accelerate because from the ...
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1answer
36 views

Relativistic Subtraction of Speeds

The formula for relativistic addition of speeds is well-known; say, if you were to have two objects travelling at each other at speeds of $v_1$ and $v_2$ (as measured by an outside observer), the ...
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1answer
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Scale diagram confusion

I’m familiar with scale diagrams where three forces act upon an object and trigonometry is used to find the resultant force, but I’ve come across questions that use units of velocity instead of force. ...
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Waves velocity for a standing wave of a string

I have done a laboratory experience to determine the speed of propagation of a wave in a vibrating magnetic string. To calculate the frequency (f) of oscillation I used an oscilloscope that calculated ...
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0answers
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Why can we parameterize a null geodesic such that its velocity is four-momentum? [duplicate]

One principle in general relativity is that the wordlines of massless particles are null geodesics. It also seem to be a commonly stated fact (for instance see eq. (3.62) in Section 3.4 of Carroll's ...
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3answers
85 views

How is final velocity negative when acceleration is in positive direction?

When a body starts from rest and starts accelerating in positive direction and moves certain positive distance, its final velocity is given by : $$v^2 = u^2 + 2as$$ Solving it gives two values of $v$, ...
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Forces, gravity, and mathematics: simulating skateboard position as a function of knee bends in a half pipe

How would a physicist explain, perhaps with the aid of a diagram, how kinetic energy in the knees is converted to kinetic energy in a skateboard as a skateboarder with little initial velocity manages ...
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0answers
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Frictional losses in flexible tubing with multiple branches opening up to a large tank

I am working on designing an experiment where I will be creating a wall-jet flow where the wall is a rotating wing. After some thought I realized I need to estimate the pressure losses due to the pipe ...
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1answer
59 views

Speed of light as the maximum speed and movement course

Assuming we have 3 objects d,e,f moving on the same line while e is stationary, d is moving to the left at 'almost speed of light' and f is moving to the right at 'almost speed of light'. What is the ...
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1answer
85 views

How does acceleration affect time dilation and length contraction?

I just studied SR and I understand how velocity affects time and length; how do they evolve during the process of reaching a certain velocity?
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7answers
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Is there centripetal acceleration with velocity of 5 m/s?

So if an object is moving at $5\ \mathrm{m\ s^{-1}}$ in a circle, is it accelerating? Me and a friend are having a conversation about this.
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0answers
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Derivation of Lagrange's Equation [duplicate]

So I was going through the derivation of the Lagrange's Equation given in Goldstein. And I have doubts about some of the steps. I would appreciate some clarifications on them. First: $$ \frac{d}{...
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1answer
52 views

Linear and angular speeds of a train

I am using Radar sensor in a train. Sensor is in the front part of the train to detect object and avoid collision. It needs vehicle motion data to calculate objects longitudional and lateral speeds....