All Questions
Tagged with motion or kinematics
4,321 questions
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What can we say about the dependence of resistive force on the velocity v of the bead?
Consider a fixed vertical circle. A large number of smooth, thin rods are fixed along the chords of the circle, all at different angles to the vertical. All the rods have their upper end at the ...
- 1
0
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0
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89
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Mandelstam variables
For a while now I have been struggling with a problem I am facing when considering the 2 to 2 process (Mandestam variables), and I would like to have an understanding of what is going on.
Considering ...
- 1,626
0
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0
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20
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Question on minimum distance between two projectiles, considering drag force [closed]
The following was a question posed in a recent test series:
What would the intended solution be to such a question? Are there any defining features that could be used to simplify the problem or is ...
- 1
0
votes
0
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36
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Vertical motion of an object under air drag and gravity [closed]
The air drag exerted on an object is proportional to its speed. Toss the object with initial speed $v_1$ upwards from the ground. If its landing speed is $v_2$, find the time of motion.
My solution.
...
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-2
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1
answer
58
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Need help in understanding Tangential Acceleration [closed]
I am studying Circular motion and I am confused about tangential acceleration and tangential velocity. I am studying uniform circular motion and it says the tangential acceleration is $0$ in uniform ...
0
votes
4
answers
107
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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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0
votes
2
answers
92
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How is the $v^2-u^2 = 2as$ modified as $v^2-u^2 = -2as$ [duplicate]
I don't understand how, when an object is retarding, its equation of motion $v^2-u^2 = 2as$ becomes $v^2-u^2 = -2as.$
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0
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1
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44
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How to find 4-acceleration scalar product in terms of $ds$ spacetime interval?
We know 4-velocity $$U^i =dx^i/ds$$ where $$ds=\sqrt{dx^idx_i}$$ so we have 4-acceleration $$A^i=dU^i/ds$$
Then we have $$A^iA_i=\dfrac{dU^i}{ds}\dfrac{dU_i}{ds}$$
How should I proceed to find this ...
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
40
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Equilibrium partitioning between two domains with different mobility
Imagine a random walk in a system consisting of two adjacent phases. In one of the phases the walker has a high mobility, and in the other low mobility.
If I'm not mistaken, the walker will in this ...
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0
answers
70
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Use of $dv/ds$ in defining acceleration [duplicate]
We can write acceleration as either
$dv/dt$ or $v dv/ds$.
And surprisingly the work-energy theorem arrives from the second definition.
I feel it would be fundamentally understanding towards work ...
0
votes
1
answer
84
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Simplification of the Differential Cross Section in Peskin and Schroeder
I am reading p. 107 in Peskin and Schroeder's QFT, and I am stucked on one of the steps they took while calculation $2\rightarrow 2$ cross section. For $A+B\rightarrow 1+2$ differential cross section ...
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2
votes
0
answers
72
views
Best way to calculate velocity, acceleration and jerk with different temporal resolutions
I have body motion tracking data I am using for my thesis. I am trying to find relationships between the kinematics of the body of speakers, and the acoustic measures of their speech (e.g. speech ...
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0
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1
answer
42
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Acceleration-time graph to travel 1 meter in 1 second and eventually reach 0 velocity and 0 acceleration
How do I go about getting an equation of acceleration in terms of time such that an object travels $1$ meter in $1$ second, given that:
At $t = 0.5$, the acceleration is $0$ and the velocity is ...
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2
votes
1
answer
100
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Can something be at rest if it has a non-zero acceleration?
I think I have a decent grasp on the physics - I understand that something can be accelerating while stationary. That's the basis of my question. I just wanted to clarify some of the language used.
We ...
- 202
2
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0
answers
127
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Shape of Trace of Chalk on a Blackboard (Kinematics problem) [closed]
A white piece of chalk is thrown onto a black horizontal board moving at constant velocity. Initially, the chalk's velocity was perpendicular to the board's direction of motion. What is the shape of ...
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-2
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1
answer
122
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Why does a graph of radius vs velocity of an object undergoing circular motion have a quadratic slope? [closed]
I'm doing a project with uniform circular motion and I cannot for the life of me understand the conceptual side of the graphs. On a graph of velocity vs radius of a bob undergoing uniform circular ...
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0
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1
answer
47
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Inertia in a different medium than air or vacuum
I have a problem understanding inertia in a medium more viscose than vacuum or air.
Let's consider the classical bus experiment.
The bus (a closed system) is accelerated or decelerated and a person ...
-1
votes
3
answers
98
views
Explaining the equations of motion in kinematics [closed]
Hi I Have these equations and I don't know and understand what each of them means.
Can someone help me?
$$\tag 1 v=v_0+at$$
$$\tag 2 x=v_0t+\frac{at^{2}}{2}$$
$$\tag 3 v^{2}=v_0^{2}+2ax$$
What does ...
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1
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2
answers
88
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Problem with logic regarding projectile motion problems when only Range and Angle are given
Im struggling with understanding a problem with my logic in regards to solving problems relating to finding out an initial velocity when given a range $d$ and angle of elevation $\theta$. The main ...
0
votes
1
answer
65
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In the kinematic equations, how is that possible while deriving an equation? [closed]
We have this kinematic equation:
$$x_f = x_i + v_it + \frac{1}{2} at^2.$$
Now, I do not have any problem with this equation, but where I have a problem with is the way we derived this equation.
We ...
0
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1
answer
28
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Why is the tangent of the rear wheel path of a bicycle parallel to the frame?
In "bicycle problems" (made famous for example by the book "Which Way Did the Bicycle Go?") the relevant point is the following: If $r(t)$ and $f(t)$ are the points of contact of ...
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1
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0
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27
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Different Directions in a general curvilinear motion in a plane (Polar Coordinates)
In a polar coordinate system, We define 4 directions:
Radial Direction: Joining the origin with particle's position (represented by r)
Normal Direction: Perpendicular to the curve at a point (...
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0
votes
1
answer
54
views
Regarding motion [closed]
I am conducting a thoughtful experiment
involving a train that accelerates at 10 m/s^2
. The train has a long passage of
12 m, and I am standing in that passage. If I jump up straight and remain in ...
user437229
26
votes
21
answers
5k
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What happens when a car starts moving? The last moment the car is at rest versus the first moment the car moves
Imagine a car that's at rest and then it starts moving. Consider these two moments:
The last moment the car is at rest.
The first moment the car moves.
The question is: what happens between these 2 ...
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0
votes
1
answer
100
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Regarding Motion
Suppose there is a train that travels from point A to point B, and some distance vertically from point A, there stands an observer, let's name them O1. Beside O1, there is another observer, O2, who is ...
user437229
0
votes
3
answers
73
views
How and why should we properly assign signs to objects in motion in opposite directions? [closed]
On a foggy day, two car drivers spot each other, when they are just 80 m apart. They are traveling at 72 km/h and 60 km/h respectively towards each other. Both of them simultaneously apply brakes, ...
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1
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1
answer
481
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Doubt in Verlet's Algorithm
In studying the temporal evolution of a system according to the deterministic model, we begin by considering a Taylor series expansion for the displacement $r$. First, we consider a positive variation ...
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0
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1
answer
27
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Plotting the displacement-time graph of a body [closed]
Suppose a body starts from point $A$ at a uniform speed of $1$ m/s. Here is the break-up of its motion:
It first travels north $3$ m.
Then it turns right and travels $4$ m.
Then it again turns right ...
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1
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4
answers
153
views
Why is $v^2= u^2-2as$ if acceleration is negative?
Why is $v^2= u^2-2as$ if acceleration is negative? Wouldn't that bring the acceleration in the answer as positive?
Suppose $v=0, \ u=90 \ \text{m/s}$, $s = 0.6 \ \text{m}$. Then, using $v^2-u^2 = -2as$...
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0
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2
answers
104
views
How to calculate the velocity of a point on a rigid body that is both translating and rotating?
I'm trying to figure out a problem involving the motion of a rigid body in 2D. The body has:
A translational velocity $\mathbf{v} = (v_x, v_y) $ at its center.
An angular velocity $\omega$ around its ...
-4
votes
2
answers
58
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Newton's third law opposing first law itself giving extra force? [closed]
If an object strikes a wall with a force $F$ and come back with same velocity in straight line only, at the moment of collision the object give force $F$ and experiences a reaction $F$, so the ...
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1
answer
45
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Confusion with classic kinematics and functions: weird results
Let think I am studying some simple system (this is a thought experiment), where I have two classic objects, and the position versus time plots follows two curves (I will left out physics constants, ...
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3
answers
117
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How to measure the velocity of a body "directly"? Is it possible?
I know that by making length and time measurements we can sometimes get a law for the movement and then calculate the velocity using calculus (it's the derivative with relation to time of the position ...
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2
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3
answers
126
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Angular velocity basics
Is angular velocity only defined for circular motion or can it be described for lets say projectile motion as well?
0
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0
answers
32
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Literature request - Dual quaternion dynamics
In my engineering practice, quaternions turned out to be much more practical than trigonometric rotation matrixes. I learned from this book on quaternions and dynamics how to describe rotation and ...
0
votes
1
answer
55
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How to calculate the force needed to make the shopping cart move? [closed]
So I have this project, where I make a shopping-cart-gokart and I would like to calculate how much force is needed for the shopping cart to start moving.
The biggest issue I had is that I could only ...
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1
vote
1
answer
81
views
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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0
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2
answers
134
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A man standing in an elevator at the third floor of a building. What is the primary factor that determines the man's kinetic energy?
Misconception in Elevator Kinetic Energy Question
I recently encountered the following question in a physics entry test exam:
Question: A man standing in an elevator at the third floor of a building. ...
1
vote
1
answer
51
views
Calculating distance between two trains [closed]
Two trains A & B of length 400m each are moving on two parallel tracks with a uniform speed of 20ms-1 in the same direction, with A ahead of B. The driver of B decides to overtake A and ...
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0
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1
answer
90
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Derivative of the product of a scalar function and a vector valued function
According to Berkeley Physics Course, Volume 1 Mechanics,
The time derivative of a vector valued function can be derived from the formula:
$$
\mathbf{r}(t) = r(t)\mathbf{\hat{r}}(t)
$$
where the ...
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0
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1
answer
53
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How to calculate angular and linear components of a force acting upon a 3d object?
apologies if this isn't worded great: I don't know all the technical terms for what I'm describing.
Given a 3D object in space (no gravity or air resistance or anything), let's say its center of mass ...
1
vote
1
answer
62
views
Deriving the fact that an approximately parabolic terrestrial trajectory is a tiny section of an ellipse
Given that $$|\vec{g}|=\frac{GM}{|\vec{r}|^2}$$ and $\vec{g}$ always points to the Earth's center of mass, can the "almost parabolic" elliptic trajectory be derived provided the initial ...
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0
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2
answers
47
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Which derivative of position as function of time can be constant in uniform circular motion?
As I understood, the x-t graph for uniform circular motion is sinusoidal, v-t is cosinusoidal, a-t is also cosinusoidal. Is there any futher derivative that is constant throughout each revolution?
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3
answers
80
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Clarification on Momentum vs Inertia in Exerting Force when Stopping
I encountered a physics question in an exam four years ago that I believe may have had an incorrect answer key. I'm seeking clarification on the correct concept.
The question was:
The property of ...
0
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3
answers
113
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Doubt about Polar coordinates
I know that for motion that does not involve rotation relative velocity of a object say $a$ with respect to $b$ can be calculated as $$\mathbb v_{ab}=\mathbb v_{ao}-\mathbb v_{bo}$$where $o$ is some ...
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1
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0
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103
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Cross Section Formula and Delta Function Identity (Eq 4.77 in Peskin & Schroeder QFT)
In the book, while deriving the cross section formula for particles A and B, a Dirac delta appears in Eq 4.77:
\begin{align}
\int d\bar{k}^z_A \, \delta\left.
\left(
\sqrt{(\bar{k}^\perp_A)^2+(\bar{k}^...
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0
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4
answers
147
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Are solids with the same density as air possible?
I was recently considering how to keep a super cheap ultrasonic range sensor safe from balls (or blocks, or whatever) going down ramps (or otherwise moving at high speeds) in a physics lab. It struck ...
0
votes
4
answers
85
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Why is the direction of friction inwards in a rotating disc even though there is no motion in the inward direction?
So, I was studying circular motion and I learnt that when an object is placed on a rotating disc, friction acts inwards to provide the necessary centripetal acceleration and facilitates the circular ...
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7
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139
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I have confusion between the concept of distance and displacement [closed]
I can't understand that why do we say that distance is a scaler quantity and displacement is a vector quantity?
Let me give some examples:
$1)$ Shyam is travelling from New Delhi to Mumbai. Now ...
