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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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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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7 answers
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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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Hexagon projectile motion [closed]

A projectile is fired from a point P with speed u at an angle  with horizontal such that it touches the vertices B, C, D and E of a regular hexagon ABCDEF as shown in the figure. The side length of ...
baldwinIV's user avatar
-1 votes
2 answers
61 views

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 votes
0 answers
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I can be both observer and object in kinematics or not? [closed]

It is a hypothetical situation | Complies several theories. | For e.g. Case 1 :- If I observe my whole body in kinematics then there will be no motion. Case 2 :-If I keep a part of my body stationary ...
Jatin 's user avatar
-5 votes
1 answer
56 views

Hi, how should I solve this problem? Thanks [closed]

Hi, how should I solve this problem? Thanks
jollyshandy's user avatar
0 votes
1 answer
26 views

How to find the other positive velocity? [closed]

A cannon, located 60.0 m from the base of a vertical 25.0 m-tall cliff, shoots a shell at 43.0° above the horizontal toward the cliff. (a) What must the minimum muzzle velocity be for the shell to ...
polimorphism's user avatar
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0 answers
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Question regarding succesive ranges of a projecticle on an inclined plane [closed]

This question is regarding the following problem: From an inclined plane a particle is thrown in a direction normal to the surface find the ratio of the successive ranges of the particle on the ...
koiboi's user avatar
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0 answers
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IE Irodov's Question on Relative Velocity [closed]

A motorboat going downstream overcame a raft at a point A; T = 60 min later it turned back and after some time passed the raft at a distance l = 6.0 km from the point A. Find the flow velocity ...
memeguy's user avatar
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1 vote
1 answer
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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
-1 votes
0 answers
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This is a question about pendulum problem in electrodynamics [closed]

Question: When two particles $A$ (charge $q_{1}$, mass $m_{1}$) and $B$ (charge $q_{2}$, mass $m_{2}$) hang from a common point by insulating threads of lengths $l_{1}$ and $l_{2}$ respectively, the ...
sp nk's user avatar
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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
42 views

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
88 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
109 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
62 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
61 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
0 answers
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Max height above the ground of a projectile on incline [closed]

This may look like a trivial problem, but it's not for me. It goes as follows:- "A particle is projected at an angle of 'x' with respect to an incline with an initial speed of 'u' from an incline ...
PROFESSIONAL ASIAN's user avatar
-1 votes
1 answer
93 views

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
40 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
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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
1 vote
3 answers
46 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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0 answers
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Why doesn't a body with uniformly varying velocity give total displacement [duplicate]

For a body moving with constant acceleration of 1 m/s2, the velocity of the body increases by 1 m/s. After 5 seconds, its velocity would be 5m/s. As the velocity was changing by 1m/s I just thought to ...
Sai Varun 's user avatar
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
74 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
36 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 answers
155 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
1 vote
0 answers
98 views

In gyroscopic effect of a quadcopter, why does precession cause torque, not vice versa?

I don't know if the header corresponds to my actual quest but i will explain. In quadcopter dynamic equations of Newton-Euler formation that I have encountered in all academic publications, torque ...
pysicsuser's user avatar
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0 answers
25 views

Third law of motion [duplicate]

Newton's third law states that for every action, there's an equal and opposite reaction. If that's the case, then how can anything move? if I push a box, then the reaction force would just cancel the ...
Ahmed's user avatar
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0 answers
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Force-simulation for graph layout: How to avoid particle collapsing into a single point?

In a force-based graph-layout simulation using Barnes-Hut, what are the conditions for collapse? With collapse I mean multiple (or even all) nodes "collapsing" into a single point. Is there ...
skep's user avatar
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0 votes
1 answer
54 views

Can distance traveled by a body be zero?

I had seen a teacher saying on YouTube that we must note that distance traveled can not be zero then I searched for the same on net and surely some sources say same e.g. the below link https://byjus....
Shinnaaan's user avatar
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0 votes
1 answer
33 views

How to decide for correct value of phase difference?

A sinusoidal wave is propagating along a stretched string that lies along x-axis. The wave is moving in +x-direction. Figure shows the graph of transverse displacement of particles of the string at x =...
Garv Chaudha's user avatar
2 votes
4 answers
176 views

Why doesn’t a cart accelerate when I push it with a constant force?

If I push a cart with a constant force, it moves at a constant velocity, so there must be no net force. The applied force must be canceled out by kinetic friction and air resistance, but the magnitude ...
jazzblaster's user avatar
0 votes
1 answer
42 views

Shaking pencil's hyperbola formula? [closed]

When you typically shake a pencil, it bends and forms a curve (hyperbola?). I want to formalize this phenomenon, but I'm not sure how to do it. I'd like to incorporate factors such as amplitude, ...
Myeongjun Chae's user avatar
2 votes
2 answers
756 views

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 ...
foolishmuse's user avatar
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1 vote
1 answer
75 views

How does relative motion work for an extended object?

I have this conceptual doubt which might be flawed very badly but I don't understand this particular thing. For example, if one end of a stick is moving with velocity $v_1$ and the other with $v_2$, ...
Krave37's user avatar
  • 123
0 votes
2 answers
31 views

Relative trajectories of two projectile [closed]

Two balls are launched with different initial velocities and at non-coplanar angles (meaning they could be in entirely different planes).Not Considering the effects of air resistance, describe the ...
user avatar
1 vote
1 answer
59 views

High school kinematics problem [closed]

From a town, cars start at regular intervals of 30 seconds and run towards, another town with a constant speed of 60km/h. At some point of time, all the cars simultaneously have to reduce their speeds ...
SHASHWAT SHARMA PHUKAN's user avatar
-2 votes
2 answers
107 views

How to Measure the depth of a Hole by Dropping a Rock? [closed]

Let's say I have a rock and a stopwatch. I am standing on the edge of a deep hole or canyon, and can see the bottom. How would I go about measuring the depth of the hole?
Arrow's user avatar
  • 101
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0 answers
21 views

Closed form solution for the linear acceleration of a particle on 3D rotating object given momentum and MoI?

Is there a closed-form solution for the linear acceleration of a particle on a rigid body undergoing some arbitrary rotation in 3D with no external forces, given its angular momentum vector and its ...
Gabi's user avatar
  • 347
0 votes
0 answers
17 views

How to mathematically model a lumped-mass cable model?

I am trying to simulate a 2D cable as a lumped-mass model. I think that it's like a chain of pendulums and I would preferably like to be damped. Just to make sure, this is the cable model that I'm ...
galtor's user avatar
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1 vote
1 answer
99 views

Lorentz-invariant phase space integral

Consider the following Lorentz invariant integral associated to a $2\to 2$ scattering: \begin{equation*} I = \int \frac{d^3\mathbf{p_3}}{(2\pi)^3 2E_3} \int \frac{d^3\mathbf{p_4}}{(2\pi)^3 2E_4} \...
Spectree's user avatar
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0 votes
1 answer
64 views

Why don't they use golf ball dimples on bullets or cannon balls? [duplicate]

Dimples help the golf ball to fly far. But do you know why they don't use them on bullets or cannon balls? Some kinds of cannon ball have similar size as a golf ball.
Creative Mania's user avatar
-3 votes
1 answer
52 views

I cannot understand the way these questions were solved [closed]

I was going through the mcqs of my physics book and i stumbled upon this pair of questions. Source of images: vaia.com 1.Figure gives a snapshot of a wave traveling in the direction of positive xalong ...
Anish Shrestha's user avatar
0 votes
1 answer
77 views

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$^\circ$. ...
NOTE Book's user avatar
0 votes
1 answer
45 views

A change in the unit vector over a finite time interval

how we can write the change in unit vectors over a finite time interval, the change in unit vectors in an infinitesimally small-time interval 'dt' is given by the magnitude of the really small angle ...
Manish's user avatar
  • 37
0 votes
1 answer
34 views

Does drag coefficient vary with size?

Take three spheres having respectively a 1 meter, 100 meters and 1000 meters diameter. Size aside they don’t differ in any other way. They’re moving through a fluid at the same, constant velocity of 3 ...
Riccardo Zanardi 's user avatar
0 votes
4 answers
96 views

Why acceleration is not always parallel to velocity but velocity is always parallel to displacement? [closed]

Velocity is derivative of displacement : $$\vec v=\frac{\mathrm {d\vec r}}{\mathrm dt}$$ And acceleration is derivative of velocity. $$\vec a=\frac{\mathrm {d\vec v}}{\mathrm dt}$$ Given that their ...
An_Elephant's user avatar
13 votes
4 answers
1k views

How do we measure the position of a body? [duplicate]

I am a high school student and I was studying kinematics about position of a body. So, one thing I do not understand in this diagram is the position of woman. Initally, at $t=0$, this woman was at $...
Armadilo's user avatar
  • 141
1 vote
1 answer
122 views

What is the point/meaning of a trajectory equation

I have just learned about the trajectory equation and it is defined as such in my textbook An equation that relates the position vector of displacement(but not distance) of a particle along x and y ...
koiboi's user avatar
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