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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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What would be the displacement-time graph for a body dropped from a certain height which bounces back to the same height after hitting a surface? [closed]

For a freely falling object, displacement-time graph looks like this: When we observe the motion of a ball thrown upwards, the graph looks like this: When the ball moves upwards retardation occurs ...
Kakiaririki's user avatar
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Work Done by kinetic friction in Circular Motion

We know when an object is moving in a circular motion on a rough horizontal surface, direction of kinetic friction is constantly. Thus, fto calculate the work doen by friction, we need to use ...
Akhilesh G's user avatar
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1 answer
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Is the answer given in the option wrong? [closed]

The question is "An Object moves along a straight line. The graph illustrates how the acceleration of the object changes with time. The direction of the motion of the object changed only once, ...
Praveen Kumaran P's user avatar
-1 votes
1 answer
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Strain energy stored in a bungee cord pulled at its midpoint [closed]

A bungee cord that behaves elastically has an unstressed length $L=.76$ m and a stiffness $k=140$ N/m. The cord is attached to two pegs, distance $b=.38$ m apart, and pulled at its midpoint by a force ...
Imperator's user avatar
1 vote
5 answers
106 views

What does it mean when vector quantity is negative?

I’ve seen in some problems that vector quantity is negative. For example, negative Coulomb means that two charges attract… negative acceleration means that object is slowing down. However, magnitude ...
Alexander Djurovich's user avatar
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5 answers
68 views

Motion of person in bus in inertial and non-inertial frame

A person is sitting in a bus that is moving with constant velocity, due to friction their is no relative velocity between bus and the person. Suddenly the bus starts to move with a constant ...
Hrishikesh Pandey's user avatar
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Interpretation of a motion in continuum mechanics with a spatial description

in the book introduction to continuum mechanics 4th edition (Michael Lai, second chapter), there is an exercice about a motion of a continuum (exercice 3.2.1). the motion is $$x1 = X1 + k.t.X2 ;$$ $$...
christian's user avatar
1 vote
2 answers
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What is the correct way to think of position?

How accurate would it be to think of position (along some axis) as the component of radius vector. Example: $$ \textbf{r} = x \hat{\textbf{i}} + y \hat{\textbf{j}} $$ And if that is correct, we could ...
Alexander Djurovich's user avatar
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1 answer
33 views

How to calculate the relative speed when three bodies are involved? [closed]

Two trains A and B start from a station and move in parallel tracks with velocities 40 kmph and 60 kmph respectively. A man sitting in train A. watches a lady who walks inside the train B at a speed ...
Sandhra Baiju's user avatar
-1 votes
3 answers
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Different results of Range of a projectile [closed]

My question is from the Range of a projectile. Range is displacement of the projectile through X-axis. We all know the formula for the range $R$ of the projectile is $$R=\frac{v_0^2\sin(2\theta)}{g}$$ ...
Riju Mandal's user avatar
1 vote
3 answers
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How much time does it take for an object to fall from space? [closed]

Let's say there's an object of mass $m$ in space, $h$ meters away from the surface of the Earth. $h$ is large enough that $g$ cannot be assumed to be constant. The acceleration varies according to ...
jazzblaster's user avatar
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2 answers
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How to find the resultant speed component, and finding the angle in which the trajectory had hit the ground?

When having a trajectory traveling over a projectile, both the vertical and horizontal velocity components must be obtained in order to calculate the resultant velocity. The question is: Why the ...
Mohammad Osama's user avatar
1 vote
0 answers
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Kinematics of a two-body decay [closed]

I suspect a flaw in the reasoning below, but am unable to pinpoint it: Is there something inconsistent in terms of the application of conservation of momentum and energy? Thanks for any hints in ...
Leonardo's user avatar
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Covariant and contravariant velocity [migrated]

I'm facing the following problem in tensor calculus: I want to calculate the velocity of a mass particle in spherical coordinates. So I'm using the following coordinate functions for spherical ...
Hans-Friedrich Pfeiffer's user avatar
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1 answer
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Extrapolating time to infinity for a particle moving spirally outward

If I have a particle moving radially away from me in a straight line and I extrapolate time to infinity, I could see the particle in a particular direction (given enough time for the light to reach me)...
Matrix23's user avatar
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Why is angular velocity vector perpendicular to the velocity vector and position vector in uniform circular motion?

I am unable to understand if the angular velocity vector is always perpendicular to both the velocity vector and position vector how does it influence anything at all and what is it's significance. ...
Madly_Maths's user avatar
2 votes
2 answers
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Physics Kinematics Equation $\Delta x = v_f\Delta t - \frac 12 a \Delta t ^2$ Derivation Using Calculus [closed]

I was wondering how you can derive the physics kinematics equation $\Delta x = v_f\Delta t - \frac 12 a \Delta t ^2$ algebraically. I understand where this equation comes from geometrically (when a=...
BakedPotato66's user avatar
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Relation bitween Mandelstam Variables in three-body final state

What is the relation between Mandelstam variables in the three body final state? There are 5 independent Mandelstam variables. What is the relationship between them?
Andrea's user avatar
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The correct dimensional formula for distance travelled in $n$th second? [closed]

I have read other similar questions on this site (including The dimensional formula of distance travelled in $n$th second with the same name), but it does not specifically answer what I was looking ...
Lakshay Rohila's user avatar
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2 answers
66 views

How many $G$ of accelaration do we experience when we come to a flat surface from a slope?

I was recently riding a bicycle when I realised that when I went onto a flat road from a short but steep slope, I felt something weird in my body as if I was expereiencing some difference in the ...
Sambhav Khandelwal's user avatar
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1 answer
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How to Express the Cross Section of a Three-Body Final State Scattering in Terms of Invariant Masses $s_{ij}$?

I'm working on calculating the cross section for a scattering process that results in three bodies in the final state. My goal is to express the cross section in terms of the invariant masses $s_{ij}$​...
Andrea's user avatar
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0 answers
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Semi-Inclusive Deep Inelastic Scattering (SIDIS) kinematics

I'm having some trouble understanding the kinematics in SIDIS. For example take the reaction $l+N\to l'+h+X$, where $l$ is a lepton, $N$ is the target Nucleon and $h$ is a hadron. The kinematic ...
rafa's user avatar
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1 answer
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Does spinning the umbrella slow down the fall more?

Ignoring its structural weakness, if you jump from some height and use an umbrella to slow down the fall, would making it spin while you're falling affect the speed in any way?
Flamethrower's user avatar
3 votes
7 answers
847 views

Physical Quantities Sign Convention

I see that almost all physical quantities carry signs. But the confusion I have is what they really mean. Does negative velocity mean decreasing velocity or velocity in the opposite direction? Does ...
Singing Account's user avatar
11 votes
1 answer
1k views

Why does the cross section of a metal after a hypervelocity impact look like that?

Look at this image of a cross section of a piece of (I assume) metal after a hypervelocity impact: I understand where the crater shape comes from, but what puzzles me is the cavity near the bottom: ...
paulina's user avatar
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1 vote
1 answer
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What happens to $\frac{d}{dt}\left(\hat{v}\right)$ at the highest point a projectile reaches when launched vertically upwards?

Acceleration is given by $\dot{\vec{v}} = \frac{d}{dt}\left( v \hat{v}\right) = \dot{v} \hat{v} + v \dot{\hat{v}}$. What happens to $\dot{\hat{v}}$ when the direction of velocity flips by $180^o$? E....
Anis Manuchehri-Ramirez's user avatar
0 votes
2 answers
79 views

Why is the displacement -time graph of an object thrown upwards a downward parabola?

So, this is the displacement-time graph of an object thrown upwards with an initial velocity $u$. I understand the first part as the equation is $s = -ut + \frac{at^2}{2}$ which is simply the ...
Madly_Maths's user avatar
2 votes
1 answer
57 views

Velocity Needed For Water To Overcome Adhesion Force To A Rounded Steel Inclined Plane

Context: I work at a fast food restaurant with a 3-module sink. The sides are slightly angled down to allow the water to trickle down into the compartments. I found that water clings to the side of ...
Rrasco88's user avatar
2 votes
2 answers
206 views

Need help regarding projectile motion

While studying motion in 2D, I came to know that when an object, projected with some initial velocity, making angle $0°$ with the horizontal, will have zero range. Its a bit confusing. The object has ...
Ishaan's user avatar
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-1 votes
1 answer
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Components of velocity in projectile motion [closed]

I came across this question in my physics textbook (Gr12) and I was hoping someone could explain the solution to me A ball is thrown horizontally off a building at $8.2\,\text{m}/\text{s}$. At a ...
Nathan's user avatar
  • 3
0 votes
1 answer
48 views

Mandelstams for $2\to 2\to 3$ process

2 initial particles become two other particles, from which one decays into 2. Let $p1$ and $p2$ be the momenta of the initial particles, $p3$ the momentum of the decaying particle, $p5$ and p6 the ...
Ville Alanko's user avatar
1 vote
3 answers
99 views

Is retardation reported with opposite sign as that of acceleration?

Does retardation have opposite sign of acceleration? For example if acceleration of a car is 15m/s² than if we are asked to report retardation will we report it as -15m/s² or simply there is a ...
NOTE Book's user avatar
1 vote
2 answers
48 views

Does coordinate acceleration match proper acceleration when $v=0, s=0$?

Alice and Bob are riding in their rocket at arbitrary proper acceleration through an arbitrary region of spacetime. Bob steps out of the space ship right next to Alice, such that at $t=t'=0$, $v=0$, ...
g s's user avatar
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0 votes
7 answers
94 views

How does the result of derivative become different from average ratio calculation?

Lets give an example. Velocity, $v=ds/dt$. If we know the value of $s$ (displacement) and $t$ (time), we can instantly find the value of $v$. But then this $v$ will be the average velocity. Now ...
Arafat's user avatar
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-1 votes
2 answers
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Problem with resources, Walter Lewin's third lecture

I've watched Walter's third lecture in 8.01 and I have a small problem with the last part, where he says that $$\vec r_t=x_t\cdot \hat x\ +\ y_t\cdot \hat y\ +\ z_t\cdot \hat z \\ \vec v_t=\frac{d\vec ...
1 vote
1 answer
62 views

Why centripetal acceleration does not causes the rotating particle to reduce the radius of its circular path?

I think that the centripetal force must develop a corresponding centripetal velocity that keeps on increasing as time passes because, $v = u + at$ Centripetal velocity constantly increases in terms of ...
Peter swift's user avatar
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0 answers
15 views

Position and displacement vector in Arc coordinate system

In Arc coordinate system the position of the particle is given by the length of the path(which is pre-determined and may also be curved) that it has travelled so how can we write it's position vector ...
Manish's user avatar
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1 vote
2 answers
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Displacement and position vectors

I know that displacement vector means a change in the position vector of a body and also that change in displacement vector and change in position vector are not the same thing, but if we talk about a ...
Manish's user avatar
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0 votes
5 answers
92 views

Motion formula gives correct answer but without formula gives wrong answer [duplicate]

Assume a body with initial velocity= 10 ms final velocity= 20 ms and acceleration= 2 ms , so the time to reach final velocity will be 5 seconds. If we try to find distance it will travel in 5 seconds ...
nitu sahay's user avatar
-1 votes
2 answers
116 views

How Fast Must a Man Run to See Rain Falling horizontally?

The fact that tan 90° is undefined indicates a key issue in the problem. Does this mean it is impossible to observe rain falling at 90 degree? When rain is observed to be falling at 90° with the y-...
Dron Bhattacharya's user avatar
1 vote
2 answers
66 views

Is the $y$-component of projectile motion independent of the $x$-component or not?

In projectile motion, it is said that both the $x$ and $y$ components are independent of each other but according to the equation of the trajectory, $$y = x \tan\phi - \frac12 g x^2/(u^2\cos^2\phi)$$ $...
Sai Varun 's user avatar
1 vote
0 answers
72 views

Angular velocity versor

I am going back through the definitions of good old Euclidean vectors and trajectories to see whether when i was younger i missed important concepts. In my notes, and reference book, i found that for ...
LolloBoldo's user avatar
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-1 votes
1 answer
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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 ...
SnoopyKid's user avatar
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0 votes
2 answers
44 views

Equations of motion for constant acceleration

I read that the equations of motion for a constant acceleration can be represented in a scalar form as well as a vector form, but what's the need to do them in vector form what extra can we do by ...
Manish's user avatar
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1 vote
0 answers
43 views

The stupidest question ever on relative kinematics and angular velocity [duplicate]

I am scratching my head on a very basic formula whose meaning escapes my intuition. On basically all texts of mechanics the following result is derived: Suppose that a rigid body is moving with ...
ebenezer's user avatar
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1 vote
3 answers
49 views

How is momentum conserved in this collision with loosely-connected spheres?

There are three identical spheres. B and C are loosely connected with a light inextensible string, and A approaches B directly at some initial velocity $v$. There is no angular momentum. A and B have ...
spraff's user avatar
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14 votes
4 answers
2k views

Why doesn't constant acceleration give me total displacement?

I started learning 1D kinematics and learnt definitions of constant velocity and constant acceleration. I thought that if a particle is changing its velocity uniformly then it has constant ...
Sai Varun 's user avatar
0 votes
2 answers
76 views

Why can't we have accelaration in the form of meters per minutes*seconds?

I have been pondering over a concept regarding the general formula for acceleration, which is widely accepted as $\frac{m}{s^2}$. This formula elegantly illustrates that a given mass or body is ...
Sambhav Khandelwal's user avatar
1 vote
2 answers
41 views

Setting $u$ = escape velocity when calculating the maximum height of a thrown object

So, if I throw an object at some velocity $v$ at an angle θ, the maximum height reached by the object is $\frac{v^2\sin^2{\theta}}{2g}$ but, I know this isnt true. clearly in a weird way, the height ...
uggupuggu's user avatar
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0 votes
1 answer
214 views

Circular motion at relativistic speed

I am working on a personal hard science-fiction project but when I analysed the following situation, in the context of special relativity my conclusion seems counter intuitive and perhaps I am ...
hello world's user avatar

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