All Questions
Tagged with kinematics speed
169 questions
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How can I detect when a car makes a turn using velocity vectors and account for speed?
I am trying to detect when a car makes a turn by analyzing its velocity vectors over time. Each velocity vector is represented as:
$$\vec{v_t} = (X_v, Y_v)$$
Currently, I calculate the change in ...
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9
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4
answers
4k
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Is it ever possible that the object is moving with a velocity such that its rate of change of speed is not constant but acceleration is constant?
Is it ever possible that the object is moving with a velocity such that its rate of change of speed is not constant, but rate of change of velocity is constant?
Like speed is only the magnitude, so ...
1
vote
1
answer
81
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How to Calculate the Stopping Distance of Train on a Complex Track [closed]
I am attempting to determine when a train should begin braking to reach a certain point at a complete stop. There are several factors that need to be considered that make this more complicated and I ...
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1
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110
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Speed is equal to distance divided by time but is this correct?
In this study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9784821/, the distance the punch travelled from start to impact is 0.49 meters and the time taken from start of punch (that's it, they define ...
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2
answers
816
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Is there a different way to measure speed, other than with time?
A second on Earth is different from a second on the Sun and a second next to a black hole. Therefore speed, as measured in meters per second, is different in each of these locations. Is there an ...
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1
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94
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Is it possible to have a uniform speed but variable velocity in one-dimension motion?
Is it possible to have a uniform speed but variable velocity in one-dimension motion? I saw a lecture where teacher said that it is possible if particle changes its direction of motion 180$^\circ$.
...
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2
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142
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Average velocity showing different results
I was solving a question, in which, a particle has travelled a distance $s$, with initial velocity $0$ and constant acceleration.
So the equation of motion becomes,
$$ v = a t \tag{1} $$
and
$$ v = \...
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261
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Why isn't the tangential velocity of circular motion zero?
Why is tangential velocity 2πr/T if the body's total displacement in the end of one revolution is zero?
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1
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228
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What does instantaneous velocity mean? [duplicate]
What does instantaneous velocity mean?
on google it says "Instantaneous means something happens very quickly, in a single moment. It's similar to the meaning of "instant", but most ...
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-5
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1
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76
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Reality of speed and time [closed]
I have a very simple question. How does a faster object takes less time for the same distance? A car with a speed of 100km per hour takes one hour to travel 100km while a car with the speed of 50km ...
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1
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48
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In circular motion is acceleration vector and $\frac{dv}{dt}$ the same?
I was studying a book in which they have written this
$$ a = -w^{2} r \hat{e} + \frac{dv
}{dt} \ddot{e} \tag{1} \label{1}$$
Where $a$ is acceleration vector $\hat{e}$ is unit radial vector and $\ddot{...
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31
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What does the square in kinetic energy formula imply? [duplicate]
I was wondering if the velocity squared imply that you need exceedingly more energy to gain speed. And if so, why is this a thing?
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2
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253
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Average angular velocity and speed
Are the magnitude of average angular velocity and the value of the average angular speed always same? If not then can you please give an example.
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54
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How long does it take to hear the sound of a plane that travels at the speed of sound?
in our physics lessons we often learn how to calculate the time that sound of a plane that travels faster than sound takes to reach us using the Mach cone.
But can we use the same method to calculate ...
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1
answer
764
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How fast can the human hand move?
I was playing with my six year old daughter the other day with her toy airplanes (I’m a pilot and she’s very interested in aviation now). I took the little F16 toy and flew it passed her as quickly as ...
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Speed and Velocity
Why did physicists develop the concept of velocity? I searched on the web, but I didn't get a satisfactory answer. All I got is that velocity has a direction whereas speed does not. Why do we need ...
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Shooting a bullet in motion
If a bullet is shot from a firearm from a moving car in the direction of movement, would the speed gained with respect to the car be same as the speed of a bullet that is shot from an immobile gun?
I’...
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Can $d/t =$ speed ever be wrong? Is there a more accurate way to determine speed?
Is there a more accurate way to determine speed? I am asking because this has to do with an accident reconstruction where my son was killed.
The investigators are trying to conclude his speed prior to ...
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2
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87
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Explain the equation
Can someone explain me this equation. This is braking distance equation that applies all reaction times ect.. Taken from Bosch Automotive Handbook.
But what does the 25,92 mean there?
v= velocity
tvz =...
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115
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$E_k = (1/2) mv^2$ doesn't make sense to me [duplicate]
I hope this is the right platform to ask stupid questions like this, but this is driving me nuts right now. Probably embarrassing to say, but I actually have somewhat of a physics background, but also ...
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What does squaring a vector mean?
So,in the 3rd equation of motion,i.e $v²=u²+2as$,what does the square on the final velocity and initial velocity actually mean?And how does it make an effect on their direction?
suppose upwards vector ...
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2
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194
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When will the 2 cars Have equal speeds? [closed]
If car1 started at 20m, with initial velocity of -4m/s and acceleration of 3 m/s^2.
Car 2 started at 15m, with initial velocity of 6m/s and acceleration of 0. At what time will the 2 cars have equal ...
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4
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749
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Car stopping times (not distances)
(Apologies if this is not the correct Stack Exchange site; I was unsure where I should post this question)
I was prompted to write this after reading on Reddit the stories told by drivers who had ...
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2
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Calculating average speed as weighted mean
In the books it says that average speed is just s/t. But I am wondering if we can calculate average speed using weighted average mean, using time or using length of path? For instance, if we know that ...
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239
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Why does it take $2d/\lvert v_1 - v_2\rvert$ time to overtake? (Can physics catch-up to math?)
The following answer is from this post.
So it becomes particularly easy to see that the opposite-direction meetings must occur at the interval $2d/(v_1 + v_2)$ and that the overtaking meetings must ...
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71
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Number of meetings of $2$ cars starting from opposite ends of a road [closed]
Question:
$2$ cars travelling at $108,75$ kmph respectively, start from the opposite ends of a $90$ km straight road. Travelling back and forth continuously for $10$ hours, how many times do the $2$ ...
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4
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908
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Mathematical proof for: Acceleration always orthogonal to its velocity changes its direction
Whenever I ask this doubt that how can force perpendicular to objects velocity can change its direction but cant change its magnitude I get proof for only the magnitude will be constant that is: no ...
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1
answer
64
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Speedometer Dilemma [closed]
This is what is written in Resnick Halliday Krane Physics Vol.1
The speedometer of a car indicates it's speed, not it's velocity, because it does not specify a direction. Speed is a scalar, since it ...
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2
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140
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Does equations of motion work for distance and speed? [closed]
In some books,when solving to find the distance and speed of the object having motion in straight line,the three equation of motion are used.so my question is whether these equation of motion (i.e $v=...
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What is closing speed?
what is closing speed? the only information google was able to give me, is that closing speed is when a car is approaching another car both at 30m/s the closing speed is 60m/s, so what exactly is ...
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1
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126
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Is this expert report wrong about basic kinematics? [closed]
This question is about the application of kinematics in an expert report for Eirikson v. Breton, ABQB 2000 798 (archived), a judgement for a case where a woman was driving a car that was accelerating ...
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1
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1
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94
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Simple difference between module of velocity and time derivative of module of position [duplicate]
What is the conceptually difference between the two:
$$\frac{d|\vec{r}|}{dt}=\frac{\vec{r}\cdot\frac{d\vec{r}}{dt}}{|\vec{r}|}\neq|\dot{\vec{r}}|\equiv \bigg|\frac{d\vec{r}}{dt}\bigg|$$ ...
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What is displacement time graph for this object which is in $xy$ plane going in sine wave like path from A to B. Also can velocity constant in path?
The path is from A to B in sine wave curve while the displacement is straight line.So how displacement is calculated for graph purpose here
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Calculate efficiency from discrete power, time and distance
I have a sequence of points from GPS and OBD for some vehicles.
Each point has the instantaneous power of the engine $(P)$, the time elapsed from the last points $(T)$ and the distance traveled from ...
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2
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170
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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 ...
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Can crooked surfaces alter speed messurement using a laser?
this might be an unconventional question yet I think the physics community would be the one to help here.
Please hear me out.
So my problem/question:
I drove into a laser speed trap with my motorcycle ...
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1
answer
333
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Distance given two velocities
I have a home trainer that is connected to an application that I am writing which needs to calculate a distance traveled given the speeds that the trainer is sending.
As such, every second, the ...
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0
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46
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1/velocity for higher dimensions
I have a somewhat basic question. I am sorry if it trivial.
Denote the velocity by $v=\frac{dx}{dt}$ suppose that $x \in \mathbb{R}^n$ and I want to parametrize $t$ in $x$ and compute $\frac{dt}{dx}$. ...
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3
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Is the derivative of the magnitude of a position vector the speed? Is the integral of the speed the magnitude of a position vector?
I'm reading a book titled "Introduction to Mechanics" by Kleppner, and I came across an example: A bead moves along the spoke of a wheel at constant speed $u$ meters per second. The wheel ...
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6
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861
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Is velocity a vector quantity? [closed]
I've read that velocity is a vector quantity. Then why do most of the people when stating the velocity of an object never use direction? Most of them usually say that 'a car is moving at a velocity of ...
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1
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Units of Linear Speed in a Circular Motion
During Uniform Circular Motion, the linear speed of the particle is defined as the radius times the angular speed.
$$ v = r\omega $$
The units of linear speed is meters/second (m/s). But the units of $...
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Why the things small seemed to move faster?
*This question might had to do with the introduction of the absolute scale.
Consider the planet that travel around the star, the length for it
to complete the orbit was in the range of the years.(The ...
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217
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How to calculate the speeds two objects need to move at in order to reach different destinations at the same time [closed]
For example: On a graph there are two points. Each point has a different destination. The distance between Point A and its destination is 50, and the distance between Point B is 100. The points will ...
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1
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162
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How does acceleration relate to the rate of change of speed?
I am given the following question:
The trajectory of a charged particle moving in a magnetic field is given by $\textbf{r}=b\cos(\beta t)\textbf{i}+b\sin(\beta t)\textbf{j}+ct\textbf{k}$ where $b,\...
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2
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187
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Variables in rectilinear motion
I wrote a post few days earlier on circular motion but it seems i still haven't got the hang of it yet. When is this equation actually true?
$s=ut+\frac{1}{2}at^2$
Suppose velocity is given by $v=t-2$ ...
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4
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720
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Velocity squared confusion
As far as I know, a vector cannot be squared. Velocity is also a vector, though we have equation of motion, $v^2=u^2+2aS$. I am perplexed with $v^2$ here. What does it imply?
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2
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325
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Finding average speed of a body traveling between two points [duplicate]
A body travels from A to B at 40 m/s and from B to A at 60 m/s. Calculate the average speed.
Can't we just add the given speeds and divide by 2 to get the average speed? This way answer would be 50 m/...
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3
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Is there any explanation from special relativity regarding the speed of a fly inside a car?
I have faced a scenario mentioned in this Question.
There was a fly inside my car and I was travelling so fast. shutters are opened in the car. I observe that when I slow down and accelerate, there ...
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2
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146
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Is it possible to derive a distance time graph from a displacement time graph?
If I take the derivative of a displacement-time function, it will give the function of its velocity over time. If I take the absolute value of my velocity function it will give me a function of its ...
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2
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104
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Is it possible to tell the speed of Shoaib Akhtar's hand after delivering the fastest ball?
Fastest bowling in cricket history is Shoaib Akhtar's 161.3 km/h.
From Google.
Then what was the speed of his arm when he delivered the cricket ball to the pitch? Is it possible to tell? Hand cannot ...
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