Questions tagged [velocity]

The time rate of change of the position of an object

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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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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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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
79 views

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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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
70 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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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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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
97 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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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
86 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
96 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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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....
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62 views

Are there any formulas that calculate the stopping distance of a car on different surfaces that include deceleration?

I already found the formula $d = v^2/2\mu g$ where '$v$' is for velocity, '$\mu$' is for the coefficient of friction between the tires and the road surface, and '$g$' is the acceleration of gravity. ...
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What happens to velocity when Time equals zero?

I am not formally educated in Science but natural questions have always intrigued me.The way I put it is that I am married to Commerce but Science has been a childhood love. Now I have this very basic ...
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2answers
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There are two velocities on the sphere. How to sum them on the sphere?

As shown in the figure, there are two velocities on the sphere, one is the velocity along the meridian direction, the arc length is its size, the other is the velocity along the equatorial direction, ...
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What's meaning of velocity of electron? [closed]

How do we define velocity of microscopic particles at small scales. As for macroscopic particle we can scale the distance travelled by object. But this is not the case with electron. Still, while ...
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Independence of position and velocity vector [duplicate]

Hi I am a mathematics student with an interest in Physics. In our Physics elective our prof. said if $\vec r$ denotes the position vector then the velocity vector $\vec v = \vec {\dot r} $ is ...
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48 views

Hyperbolic motion with non-zero initial velocity

The equations of hyperbolic motion in a single spatial direction with initial velocity of zero are pretty easy to find given a bit of googling, such as in this answer. And while I'm too rusty at ...
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1answer
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Rapidity in 4-vector Transformation

In Lorentz transformation we have a concept of rapidity as related to boost. Rapidity is defined as a hyperbolic angle α such that $$\tanh(α)=v/c .$$ This further defines a matrix for Lorentz ...
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Vertically move in a helicopter to go somewhere on Earth [duplicate]

Is it possible to go from point A to point B (which are on same latitude) by hovering above A and wait till the earth rotates to point B below and then come down vertically? I believe there would be ...
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2answers
108 views

How to decelerate from velocity $v$ to stop time $t$ over distance $d$? [closed]

I'd be grateful for some help with this problem I am trying to solve. Let's say that I have an object travelling at a velocity $v$. I want that object to come to a halt in time $t$ AND travel exactly ...
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35 views

Speed is different when differentiating a function and when not differentiating

I have the function, $S(t) = t^2$. When Finding speed $= V = \frac{dS}{dt}$, we get $V = 2t$. Now If, I don't differentiate it and simply put $V = \frac{Distance(S)}{Time(t)} = \frac{t^2}{t}$ We ...
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Confusion about average value of $v^2$

I know that expected value of velocity means $$\langle v\rangle=\frac{d\langle x\rangle}{dt}$$ and since I know how to calculate $\langle x\rangle$ namely $$\langle x\rangle=\int_{-\infty}^{\infty}x|\...
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Velocity addition formula derived from velocity boosts

I understand the derivation for the equation the velocity in a boosted frame by taking the boosts of the differentials such that: $v'^{\mu}= \frac{dx'^{\mu}}{dt'} $ where $x^{\mu} = \Lambda^{\mu}_{\, \...
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1answer
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Dynamically changing acceleration of object moving towards sun due to gravity

For a collection of sci-fi short stories set in the rather near future I need an approximation of the time it would take a space ship to travel from an Earth orbit to Ceres. In a previous story of ...
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1answer
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Does Horizontal Velocity remain constant when it hits a surface in a Parabolic Motion?

It is told in one of the answers that the horizontal velocity stays at 4.0 m/s after the ball bounces from the plate. Why is it still at 4.0m/s, isn't there friction or is it neglected for the sake ...
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Why isn't acceleration always zero whenever velocity is zero, such as the moment a ball bounces off a wall? [duplicate]

The answer to this homework problem is $\left(\text{D}\right) :$ I understand why we rule out options $\left(\text{A}\right)$ and $\left(\text{B}\right)$ first. However, I don't get why $\left(\...
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The chain rule and velocity transformation in relativity

From elementary calculus, we have that the chain rule occurs when we differentiate a function like $f(y(x)) \equiv f(x)$: $$\frac{\mathrm{d}}{\mathrm{dx}}[f] = \frac{\mathrm{d}}{\mathrm{dx}}[f(y(x))] ...
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1answer
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Spring mass system

While solving some spring block questions one doubt came in my mind ..is it possible to calculate maximum velocity of a point between two springs of different force constant attached to a block of ...
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1answer
56 views

How fast will air travel to fill a vacuum?

Suppose I have a sealed glass cylindrical vessel of radius r and length l that is evacuated. I smash one end. How long will it take for air to (a) reach the end of the cylinder (b) fill the vacuum ...
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111 views

What happens to $P = F × v$ for a car moving on a frictionless surface and in vacuum?

I'm considering a scenario in which a car with an engine capable of producing maximum power of 200 hp is moving on a frictionless surface and in vacuum. Since no work is lost due to friction or air ...
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1answer
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Signs in relative vector addition

So I know the formula for relative vector addition is $$w = \frac{v-u}{1-\frac{uv}{c^2}}.$$ How do I chose when to use this formula or its inverse transformation for solving vector addition problems ...
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2answers
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How does the mass distribution and center of gravity affect the speed of a lego car down a ramp? [closed]

we are doing a research involving motion of an object with a nonuniform mass distribution, and we have to explain how mass concentration, mass distribution, and center of gravity will affect a Lego ...
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1answer
51 views

In the equation for acceleration (with known $v$, $u$ and $s$) why velocity is squared and displacement is multiplied by 2? [closed]

In the following equation $$a = \frac{v^2 − u^2 } {2s} ,$$ where $v$ is the final velocity, $u$ is the initial velocity, and $s$ is displacement. Why is velocity squared and displacement multiplied by ...
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Confusion on Horizontal & Vertical Components of a Parabolic Motion

This was a question I found about projectile motion, the question was what's the bike's speed when it took off. Using $S=ut + 0.5at^2$, the time taken to reach the ground is $0.505 s$, they used ...
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A basic question on Heisenberg uncertainty and experiment

I’m not a physicist or anything even close. But what I understand from the reason for the Heisenberg uncertainty is that the photon is changing the volecity/momentum when it hits the particle. ...
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66 views

What is the difference between velocity and speed? [duplicate]

What is the difference between velocity and speed? could anyone describe it more specific? does velocity have direction?
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Doubts in understanding the instantaneous velocity [duplicate]

I was studying about the fundamentals in physics and I read a defination of average velocity. It was like that average velocity is a physical quantity which gives the measure of overall rapidity of a ...
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2answers
88 views

The maximum velocity of an object in water [closed]

Suppose we have the mass and volume of an object, like a sphere, with density less than water. We grab it under the water and leave it, so it will fly up to the surface. What will be the maximum ...
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Which is more important for a force of the impact mass or velocity? [duplicate]

If a 2 times bigger mass collides with an object in which a 2 times smaller mass collides but with 2 times the speed which one will produce more force on the object? The object is stationary before ...