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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0answers
27 views
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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0answers
33 views
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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2answers
55 views
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
40 views
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
5k views
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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11answers
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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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0answers
11 views
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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2answers
27 views
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
12 views
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
42 views
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
82 views
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
42 views
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
69 views
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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0answers
35 views
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
59 views
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
82 views
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
37 views
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
97 views
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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0answers
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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
84 views
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
68 views
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
18 views
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
64 views
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
97 views
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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0answers
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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
32 views
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
196 views
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
44 views
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
69 views
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
34 views
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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0answers
16 views
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
24 views
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$$
Solving it gives two values of $v$, ...
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0answers
7 views
Forces, gravity, and mathematics: simulating skateboard position as a function of knee bends in a half pipe
How would a physicist explain, perhaps with the aid of a diagram, how kinetic energy in the knees is converted to kinetic energy in a skateboard as a skateboarder with little initial velocity manages ...
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0answers
16 views
Frictional losses in flexible tubing with multiple branches opening up to a large tank
I am working on designing an experiment where I will be creating a wall-jet flow where the wall is a rotating wing. After some thought I realized I need to estimate the pressure losses due to the pipe ...
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1answer
59 views
Speed of light as the maximum speed and movement course
Assuming we have 3 objects d,e,f moving on the same line while e is stationary, d is moving to the left at 'almost speed of light' and f is moving to the right at 'almost speed of light'. What is the ...
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1answer
85 views
How does acceleration affect time dilation and length contraction?
I just studied SR and I understand how velocity affects time and length; how do they evolve during the process of reaching a certain velocity?
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7answers
93 views
Is there centripetal acceleration with velocity of 5 m/s?
So if an object is moving at $5\ \mathrm{m\ s^{-1}}$ in a circle, is it accelerating?
Me and a friend are having a conversation about this.
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0answers
75 views
Derivation of Lagrange's Equation [duplicate]
So I was going through the derivation of the Lagrange's Equation given
in Goldstein. And I have doubts about some of the steps. I would appreciate some clarifications
on them.
First:
$$ \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....
