Questions tagged [kinematics]

The description of the movement of bodies by their position, velocity, acceleration (and possibly higher time derivatives, such as, jerk) without concern for the underlying dynamics/forces/causes.

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Kinematics constant acceleration problem

A stone is being thrown vertically upward with a speed of 12.5m/s from the edge of a cliff 75.0m high, what’s the total distance did it travel? It is a constant acceleration kinematics problem, I ...
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Understanding where equation $2.3$ comes from?

I'm trying to understand this paper (equation $2.3$ specifically): Bini, D., Carini, P., & Jantzen, R. T. ($1995$). Relative observer kinematics in general relativity. Classical and Quantum ...
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Why does the amount of rope unwound from a spool correspond to its change in center of mass?

Consider a spool wound up with rope and a person pulling the spool, in such a way that the spool rolls in that direction. I know intuitively that the amount of rope unwound equals the displacement of ...
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Why is the complex time not considered in the solution?

In the solution, why is the the complex time not considered and real and positive time is considered? Is it because complex time does not exist or there is some other reason?
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Does equations of motion work for distance and speed?

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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Why we don't differentiate even if $u$ and $a$ aren't given as constants in question? [closed]

So please help me. I am not understanding why the heck u and a aren't being differentiated in spite of not being constant(or they are???).
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What is the relative acceleration of a ball thrown inside a bus with respect to a man sitting inside if bus has uniform velocity? [closed]

Like both man and ball are experiencing acceleration due to gravity so will the ball have no acceleration w.r.t to man?
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Do moving objects "contain" kinetic energy? [closed]

We know that kinetic energy is relative to the reference frame. In a frame moving with the object, the K.E. will be zero. So is it misleading, or completely wrong, to say that a moving object "...
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Stopping too soon [closed]

I have an object going $1000\frac ms$, $vi$, that I want to slow down to $250 \frac ms$, $vf$. I want it to slow down in $10000m$, $d$. I want to know how much deceleration is necessary, and how long ...
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What is a constant vector?

If the acceleration vector and velocity vector are antiparallel and constant vectors(?) what is the type of motion of the particle/body? Also, what are constant vectors?
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On the motion of a particle [closed]

A particle starts from the origin at $t = 0$ under a variable acceleration $\alpha$, it stops at $t = 1$ at $(0,1)$, provided that the motion takes place along the x-axis. Show that: i) The value of $\...
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How do I study for vectors? [closed]

I live in India and I am currently an 11th Grade student. I am having difficulty studying physics, specifically Vectors and Kinematics. I have Concepts of Physics Part 1 and while its enlightening, I ...
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Query Regarding circular motion [closed]

Suppose a particle is moving with tangential acceleration of constant magnitude but with centripetal acceleration magnitude variable with time (suppose proportional to $\,t^2$). Then what does the ...
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How to calculate total sum of orientation changes in 6 DOF data from a Motion tracker?

I'm using data from a motion tracker that give provides 6 coordinates for every frame ( with frame rate of 240Hz) Position: x, y, z Orientation: azimuth(yaw), elevation(pitch), roll I can calculate ...
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Acceleration in terms of displacement

I am having problems understanding the derivation of acceleration in terms of displacement. The first step is fine: $$a(x) = \frac{\mathrm dv(x)}{\mathrm dt} = \frac{\mathrm dv(x)}{\mathrm dx} \frac{\...
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What is the difference between constant and uniform acceleration? [closed]

What is the difference between constant and uniform acceleration ?
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Motion in one dimension. One car overtaking a different one [closed]

I stumbled upon this exercise: From this book. The problem I have is that I cannot understand author's mathematics from the solution: Precisely: what did he do in the step "Eliminating t ...
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Angular velocity at a general point

I have been reading circular motion for a while and the magnitude of angular velocity is defined as component of linear velocity (perpendicular to the position vector) divided by position vector. But ...
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How important is the concept of rapidity in relativity?

After studying the concept of rapidity and the associated formulation of special relativity in terms of hyperbolic trigonometric functions of rapidity, I've come to understand the elegance of this ...
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Scalar term for acceleration [duplicate]

Consider the following definitions: Distance is the magnitude of the displacement Speed is the magnitude of the velocity X is the magnitude of the acceleration Is ...
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Why should I find value of constant of integration instead of using definite integration?

$v = 2t$, find $s$ (displacement) at 3 seconds if at $t=0$ body is 2m behind origin. My teacher said that I cannot use definite integration as we do not know the boundaries for time, so I have to ...
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What does instantaneous displacement really mean?

I've read and (I think) understood that instantaneous velocity is the velocity of an object for an "infinitesimally" small time interval: $$ \lim_{\Delta t\to0} \frac{\Delta s}{\Delta t} = \...
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Is friction equal to gravitational force during rolling down a ramp?

I'm studying the motion and forces involved in a ball (bidimensional) rolling down a ramp inclined by an angle $\theta$ from the x-axis. This is the body diagram (I didn't draw forces but there is ...
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What happens to velocity if mass changes, in uniform velocity motion of a body? [closed]

If a body is in motion with some constant velocity, but its mass is decreasing as it is moving forward, what will happen to its velocity? Does it stay constant, why?
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Linear Acceleration, Frames of Reference and the Laws of Physics

Alice and Bob, observers in deep Galilean spacetime, have identical rocket ships. Alice is at rest relative to an inertial frame. At $t=0$ she accelerates with acceleration $a_0$ in a straight line ...
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Is there anything like negative deceleration?

I kinda understand acceleration, deceleration and negative acceleration but does anything like negative deceleration exist?
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On relativistic kinematics of particle accelerators

While reading these lectures I came across the following Putting together the first two formulae one reads $M=E_{cm}$, or equivalently, the centre of mass is always at rest. But is it true? It might ...
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How to determine the units of the terms of a function relating two physical quantities?

While studying kinematics I came across a problem which said, A particle is moving along X-axis, its position $x$ varying with time $t$ as $x(t) = 2t^3 - 3t^2 + 1$. Now, that is not the full problem ...
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Upper and lower limits of integration in the derivation of kinematic equations?

I have already read part of this answer, but I need further clarification. In the derivation of kinematic equations, the following two lines are present: Acceleration is constant. $\text dv=a\text dt$ ...
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Peskin & Schroeder's QFT book page 167

I am wondering how to get below equation (above eq.(5.104)) on Peskin & Schroeder's QFT book page 167: $$ y\simeq\frac{1}{2}(1-\cos\theta)\simeq 1-\frac{\chi^{2}}{4}. $$ Here, the book try to ...
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Projectile motion question - finding launch angle given only range and initial velocity [closed]

this is a first year physics problem about projectile motion, which I usually am pretty good with but this question confused me because it doesn't state that the motorcycle lands on the same elevation ...
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Proving the equivalence between max range for a fixed speed and min speed for a fixed range for a projectile

https://math.stackexchange.com/a/2663051/ In this post which was accepted as solution the answerer said "By the way, proving that the maximum range in a slope (or minimum speed to a fixed range) ...
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Kinetic energy with respect to center of mass frame (COM) [closed]

Let there be an object having some chemicals in it. It starts moving with a uniform velocity $v$ and a chemical reaction starts happening. In this case, which of the following statement/s is/are ...
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Generalize knowing when to accelerate towards or away from a target you are moving towards to arrive without overshooting it

Imagine you are a spacecraft moving towards a position and you start out with zero relative velocity. You accelerate towards it, then halfway there you start accelerating in the opposite direction so ...
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Understanding the meaning of the two below expressions related to rate change [duplicate]

We know that velocity vector $\vec{v}$ is given by $\frac{d\vec{r}}{dt}$ where $\vec{r}$ is the position vector of a particle carrying a 2D motion . I would like to know what then $\frac{d|\vec{r}|}{...
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What does "$L$ seconds" mean in $\lambda = 0.225L \ \rm s$? [closed]

I was reading a paper, (Iannou et Chien 1993) and they were trying to determine the exact amount of reaction time on the California safety spacing rule, and the result was: $ \lambda = 0.225 L\ \rm s$ ...
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Can elastic mediums snap at a faster speed than the wave which travels in it?

The speed of wave in an elastic medium is given by Velocity of Longitudinal Wave 1) Velocity of Sound in any Elastic Medium: It is given by $v=\sqrt{\frac{E}{\rho}}=\sqrt{\frac{Elasticity\,of\,the\,...
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I have a question about explanation of inertia of motion of a body by pseudo force

If a bus stops moving suddenly, we tend to fall forwards due to the inertia of motion of our upper body. But can we explain the sudden jerk in the forward direction due to some pseudo force? (Because ...
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Easy mechanic question

A man is walking down a street, he wants to avoid touching any rain drops. Walking with a velocity of $v$ and rain drops falling at $u$. He has an umbrella with radius of $r$ and his height is $h$. ...
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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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Difference between geodesics on surfaces and paths under gravitiational fields

Sorry for the maybe silly question, but I'm a math student and I'm not able to find the answer to this question from the physics point of view. Let us suppose that a ball is set in a non equilibrium ...
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Threshold energy for pair production from proton-electron collision

In this undergrad nuclear physics problem I am asked to find the kinetic energy threshold for an electron colliding with a still proton to create an electron-positron pair. So in short: $$e^- + p^+ \...
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Constant acceleration problem [closed]

A spaceship departs from the origin of the LCF Σ and moves along the $x$-axis with constant proper acceleration $a = 10 m/s^2$ until it attains the speed $v = 0.5 c$. Calculate the time the spaceship ...
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Find the maximum distance the ball will travel [closed]

A ball is being thrown at initial speed of $v_0=7$ m/s with an angle $\theta$. I am trying to find the maximum distance the ball will travel before hitting the ground. At first i wanted to find the ...
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Differentiation [closed]

Why is $$\frac{d}{dt}v^2=2v\frac{dv}{dt},$$ When: $$\frac{d}{dx}x^2=2x,$$ where $v$ is velocity? I don't understand why the variable $x^2$ has the derivative of $2x$, whereas the variable velocity has ...
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The value of $g$ in free fall motion on earth [closed]

When we release a heavy body from a height to earth. We get the value of $g=9.8 \ ms^{-2}$. Now, I'm confused about what it means. For example, does it mean that the body's speed increases to $9.8$ ...
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Acceleration on a body in free fall inside a elevator which is going up [closed]

A stone is released from an elevator going up with an acceleration a. The acceleration of the stone after the release is? Answer to this question is only g. But why does a does not influence the stone....
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What radius should you take while converting rpm to m/s? [closed]

When converting rpm of, say a helicopter blade, to m/s, the equation used is:$$v_{m/s} = \frac{2\pi{r}}{60}\times N_{rpm} $$ In the equation, we have radius as a variable, as the speed changes with ...
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3 votes
2 answers
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Faster Small Tires vs Slower Large Tires [closed]

We have two tires with radius r and R respectively. They are connected to two almost identical vehicles with same net mass. "Almost", because Gear ratios are adjusted such that At equal ...
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How does negative velocity and positive acceleration exactly and vice versa slow down objects?

I am kinda confused how does negative velocity(-v) and positive acceleration(+a) exactly and vice versa slow down objects? i have a thought about it please let me know if i am correct. according to ...
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