Questions tagged [velocity]
The time rate of change of the position of an object
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Confusion on higher derivatives of position [closed]
If I apply a force to a stable object and it moves, the resultant force is $>0$ (Newton 2nd law). Ignore any frictional forces:
acceleration occurs and changes from $0$ to something $>0$ say in ...
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2answers
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Why do things stop accelerating?
Before $t=0$: object is not moving
At $t=0$: I push object with sufficient force to overcome static friction
After $t=0$: Object accelerates. Resultant force is greater than $0$. Dynamic friction is ...
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2answers
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Dependence of Lorentz factor on only a component of velocity
In cases of two- or three-dimensional space, why doesn't the Lorentz factor of a component of 3-space momentum depend on only the corresponding component of velocity? That is, why isn't there, for ...
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1answer
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How is the Rapidity Vector Calculated from Velocity Vector and vice versa in special relativity?
How is the Rapidity Vector calculated from Velocity Vector in 3-D and vice versa in Special Relativity?
What I want is to take 2 3D Velocity Vectors, convert each to corresponding 3D Rapidity Vectors, ...
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1answer
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Why is the speed of a quantum particle defined as coefficient of $t$ over coefficient of $x$?
I’m currently studying quantum mechanics from Introduction to Quantum Mechanics by Griffiths. In his free particle section, he says that the speed of a particle is the coefficient of $t$ over the ...
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Motion in one dimension calculating accelaration [closed]
An athlete; Jayleen, starting with an initial velocity of 4m/s; runs with constant acceleration for 6s. Her velocity is measured as 13m/s. What is her acceleration in m/s2?
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1answer
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How does the size of a valve opening determine liquid velocity and pressure?
Say we have a water reservoir with a valve near the bottom to allow water to be released into a separate reservoir (for example, in order to avoid flooding). The valve is initially slightly (10%) open,...
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4answers
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Why does fluid pressure decrease as fluid velocity increases according to Bernoulli's principle?
I’m studying aerodynamics. I understand Bernoulli’s principle very well, I just can't wrap my head around why pressure decreases as velocity increases. Like the garden hose example: if you cover the ...
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1answer
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Can you equate relativistic mass to rest mass? [closed]
I am doing a project with the Inelastic Collison equation and was wondering whether you can insert a relativistic mass into it or whether you can only use rest masses. If you can, is there any ...
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2answers
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Changing mass with velocity
I was wondering that a change in velocity can change the mass of an object slightly. I thought of this since p=mv so if we rearrange it to be m=p/v. Does this mean that a change in momentum or ...
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Find the velocity of $v$ [closed]
In the arrangement shown in the figure the ends P and Q of an inextensible string moves downward with uniform speed u. Pulleys a and b are fixed. The mass M moves upwards with what speed?
How can v ...
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3answers
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Is $ d \mathbf v · d \mathbf v = d \mathit v^2 $?
My teacher has proved the following:
$$ \mathit v^2 = \mathbf v·\mathbf v = \frac{d\mathbf r}{dt}·\frac{d\mathbf r}{dt} = \left(\frac {ds}{dt}\right)^2 \Rightarrow \mathit v = \frac{ds}{dt} $$
Because ...
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The derivative of the unit velocity vector
The set up:
An intertial frame Y-X used to describes trajectory of an insect on some rigid body using some relative vectors. Symbols: $ \vec{r_a}$ is is the vector connecting the origin to some point ...
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1answer
37 views
Calculating flow rate through a mesh
I want to calculate the flow rate of water through holes in a mesh.
In the following hypothetical situation water is flowing through a 13mm diameter pipe at a velocity of 3 meters per second and a ...
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0answers
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Why are drag and kinetic energy proportional to velocity squared? [duplicate]
For example, it takes a car four times the kinetic energy to travel the same distance at twice the speed, which quadruples the drag experienced by the car. This observation is described by the ...
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Would a navigator announcing ship velocity whle approaching lightspeed make linear announcements?
Given my admittedly limited understanding of relativity, I believe that as a hypothetical space ship approaches the speed of light at a constant acceleration, what the crew would "see" on ...
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1answer
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Difference between $u$ and $v$ as velocity variables in special relativity [closed]
I am beginning to learn about special relativity, so I apologize for the (most likely) basic question.
I frequently see, for example, the Lorentz Factor given by the equation $\gamma = \frac{1}{\sqrt{...
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1answer
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I don't think I understand how to calculate the distance of when objects are passing each other
You are driving a SUV with constant velocity of 22m/s. At a moment, you notice a truck 200 meters ahead of you, moving in the same direction with constant velocity 18 m/s. How far your car should ...
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3answers
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Is an accelerating velocity the same as an identical non-accelerating velocity?
I’m referring to an instant in time where the velocities of two different particles are identical. One particle experiences a force and the other does not. I think their states of motion are different ...
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1answer
26 views
Velocity of Sound with an Increase in Pressure
Why does the velocity of sound not increase with an increase in pressure? Let me take an example. Suppose there exists a gas at some pressure. With an increase in pressure, it would turn into a liquid....
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1answer
44 views
Acceleration in a space without friction [closed]
If an object is accelerated by one point (say, at 09:00 objected is forced) after no force is applied to the object in a space without friction, does it move forever...?
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1answer
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Does Hubble's constant apply to galaxies that are blue-shifted/ moving towards us? Another question
Does Hubble's constant apply to galaxies that are moving towards Earth with a velocity and does Hubble's constant also able to different systems such as binary stars, stars in another galaxies or ...
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1answer
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Find COM velocity with respect to laboratory reference frame
I'm trying to solve the following homework question.
Suppose that in the laboratory frame of reference we have $2$ particles. Particle "$a$" is at rest with total energy $E_a$, while ...
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1answer
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Solving for Initial Velocity [closed]
A ball is dropped from the building 150 m high at the same instant a second ball is thrown upward from the ground. If the two balls pass each other at a point 60 m above the ground, solve the initial ...
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1answer
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Is the velocity variable in the conservation of momentum equation always relative to the ground?
I haven't found anything written about this explicitly but from the questions I have done this seems to be the case. Is the velocity in $m_1v_1=m_2v_2$ always relative to the ground (or at least ...
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2answers
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How momentum is dual to the velocity vector at a point on a differentiable manifold?
The tangent space $T_pM$ which is a real vector space on a point $p$ of a differentiable manifold $M$, has a cotangent bundle $T_p^*M$ at $p \in M$, such that for any $v \in T_pM$ and for any $w \in ...
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3answers
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What is the effect of the mass of object on its acceleration? On its velocity? [closed]
A short answer will do, thankyou!
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4answers
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Why do the two balls come down at the same time?
I saw this video on YouTube in which two balls slide down on different inclines.
The part which confused me was the one at 2:00 seconds. I couldn't understand the physical reason for that.
If we drop ...
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2answers
61 views
Direction of velocity and displacement
Do velocity and displacement always have the same direction? I know this seems like a silly question to ask, but I'm having a hard time coming up with any counter examples, and I'm not able to prove ...
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1answer
16 views
Interpreting recession velocity (red / blue shift)
I just had to teach something that I myself have never learned, concerning recessional velocity of galaxies. Awkward!
The question was: "A line in a hydrogen spectrum has a wavelength of 486.1nm ...
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2answers
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Why do two similar objects not hit the ground at different times?
The formula for air resistance is $$F_{air}=\frac{1}{2}\rho cAv^2 $$
where $\rho$ is the density of the air, $c$ is the drag coefficient, $A$ is the cross sectional area of the object and $v$ is the ...
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Relative Velocity and Mass
Under what conditions can you just add velocities? For example if I throw a paper ball in the air in a 1m/s wind the ball should move in that direction at 1m/s as it falls according to relative ...
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Needed force to reach specific point for the ball
I am making a billiard game and need to push white ball to move other balls which should pocket so I need to calculate the force. I have mass, friction, distances, angles, collision point, origin ...
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2answers
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What is the difference between non-uniform velocity and acceleration?
So I know non-uniform velocity as, "Non-uniform velocity is when an object covers unequal distance in equal interval of time in a particular direction or covers equal distance in equal interval ...
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1answer
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Relativistic velocity addition - algebraic structure?
The relativistic velocity addition $\oplus$ for 3-velocities $\bf{u}$ can be constructed from Lorentz boosts $\Lambda$ acting on 4-velocities $u$
$$ u \to u^\prime = \Lambda(v) \, u \implies \bf{u}^\...
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2answers
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Velocity operators in quantum mechanics
According to the Heisenberg equation of motion, the velocity operator is given by
$$\hat{v}=\frac{d \hat{r}}{dt} = \frac{1}{i\hbar}[\hat{r},\hat{H}].$$
Question 1: How can I find the velocity operator ...
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Velocity Question from grandparent
My Grandparent asked me this question a few years ago, and I am getting around to giving him an answer, but I don't know the answer. Can anyone help?
"A pickup truck is speeding along a highway ...
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1answer
43 views
Does maximum velocity change when vertical mass-spring system is used in different location on Earth in SHM?
Let me elaborate for you my concerning
I am thinking of a example of a vertical mass spring system. Suppose i place my system at equator, let suppose a wall clock which uses a vertical spring mass ...
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1answer
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Sig Figs when finding Slope [closed]
When finding the slope of a position vs time graph, do you use sig figs?
For example, if the slope is 150m/10s, would the answer be 20m/s (because the least amount of significant figures in this is 1),...
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2answers
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How to create a position-vs-time graph from this?
I'm given the following problem:
At what times is the particle found at $x= 20m$?
I know this is a very fundamental problem, but still I cannot see how the answer ends up being $4$ and $12$. Note ...
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1answer
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In terms of being on an elevator, velocity, acceleration and forces, how are they related?
Before you answer, read this: Say you are on an elevator, and for some reason, when in it and you jump, you have a different velocity from the elevator, say the elevator is at 15 MPH and you are ...
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1answer
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Splitting a varying distance into constant acceleration and deceleration periods
I am moving a tool over a varying distance. My motors can support constant acceleration and deceleration of $1 \space m/s^2$. I need to cover the distance as quickly as possible (accelerate for as ...
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Do charged particles move along the electric field line?
I was discussing with my friend about electric field lines and he said that:
given a test charge at rest at a point in the region of the electric field the charge will continue to move along the path ...
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3answers
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What is the velocity of an object sitting on the surface of the Earth in General Relativity?
In General Relativity an object on the surface of the Earth feels a force from the Earth due to the surface of the Earth's constant acceleration through space or space-time.
From what I've heard time ...
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0answers
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Velocity operator for Hamiltonian that satisfying generalized Schrodinger equation
The velocity operator is defined as $\mathbf{v}=\frac{i}{\hbar}[H,\mathbf{r}]$ for the Hamiltonian $H$ satisfying $H\psi=\epsilon \psi$. What's the expression of $\mathbf{v}$ for $H$ satisfying the ...
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Hello, can anyone please help me understand and solve the problem? [closed]
ABCD is a track with a horizontal section BC of length 5 m. A 0.3 kg steel sphere is released from a point on the slope AB and it rolls towards the end D of the track. A stop watch was started shortly ...
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2answers
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If hypothethically a car tries to go in two different directions at the same time, which direction will it end up going?
When we add two vectors(A and B), we get one resultant sum vector(C).
i.e. adding two different directions gives us one resultant direction.
So in the same way if a hypothetical car was trying to go ...
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5answers
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Significance of $\frac{dv}{dx}=0$
Suppose an object is moving with varying acceleration in time.
What does it mean when it hits a point where $\frac{dv}{dx}=0$?
Does it mean the object has hit maximum velocity?
Assume the object ...
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1answer
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Is propagation speed depending of wavelength? (QM)
In case of a single free particle, no potential field, the wave function is:
$$ \Psi = A e^{i(kx-\omega t)}. $$
As it must fulfill the Schrödinger equation
$$ - \frac{\hbar^2}{2m} \nabla^2 \ \psi(\...
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3answers
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Why can't we tell, we are moving?
I stumbled upon this question:
Can we really not tell if we are moving?
and it made me start thinking (probably a bad idea for a non-physics guy).
To my knowledge, moving at relativistic speed means ...
