Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

-1
votes
1answer
51 views

Physics theory/concept behind this question [on hold]

The question is: Two cars start off at the same location and move away at constant velocities. At $t = 0 s$ car $A$ moves away with a velocity of $12.5 m s^{−1}$ NORTH and car $B$ moves away with a ...
-4
votes
0answers
21 views

Quarterback Question [on hold]

Quarterback passes football at 8.00m/s at angle of 31.5 degrees above horizontal. How far does it travel horizontally (assuming it is caught at the same height it is thrown)?
0
votes
2answers
32 views

Kinematics of particles

Do particles have to move in a straight line to apply Suvat equations? I always perceived that they do because acceleration can mean a change in the magnitude of velocity, a change in direction or a ...
-1
votes
0answers
58 views

Find number of collisions [on hold]

A ball dropped from a certain height,falls in the influence of uniform gravity,strikes the ground and rebounds elastically.During a time interval t=8s from it was dropped,it covers a distance s=20m....
-1
votes
0answers
19 views

Relative motion: rain man problems [on hold]

When a man moves down the inclined plane with a constant speed 5 m/s which makes an angle of 37° with the horizontal, he finds that the rain is falling vertically downwards. When he moves up the same ...
5
votes
3answers
78 views

Why do office chairs rotate when pushed/pulled out?

A common source of frustration when I'm at work is the fact that my rolling office chair's wheels rotate whenever I push it forward or backward from my desk, which can cause it to bump my computer ...
0
votes
0answers
39 views

Why does Stirred (rotating) coffee alters cup’s resonance frequency? [duplicate]

I place a spoon in my cup of (dolce gusto lungo) coffee and tap the bottom of the cup with my spoon. It emits a certain (fixed) frequency. However, if I stir the coffee (but not so fast that the ...
0
votes
1answer
37 views

Centre of mass and conservation of momentum [closed]

A bullet of mass $50$ g moving with velocity $600$ $m$ $s^{-1}$ hits a block of mass $1$ kg placed on a rough ground and comes out of the block with a velocity of $400$ $m$ $s^{-1}$. The coefficient ...
-2
votes
0answers
22 views

How to find average speed? [closed]

A ball thrown up from the ground reaches a maximum height of 20 m? Find the average speed between t = 0.5 s and t = 2.5 s. Hint: Split the interval in two parts by using the time instant ( t = 2 s). ...
-4
votes
0answers
83 views

Friction, motion and weight [closed]

$Q1$. Two toddlers, Barry and Olivia are playing on a slide. Barry is sitting on the slide which is inclined at $31^{\circ}$ below the horizontal. His friend Olivia is sitting behind Barry on a flat ...
0
votes
0answers
15 views

Relationship between angle of banked road and normal force and its component [migrated]

Why are these two angles in the diagram below equal? I can't quite see their relationship or proof of why they are the same.
1
vote
1answer
42 views

Thomson Exercise 2.12: Why is $p_i^2 = m_i^2$?

I'm just working on some problems from Thomsons Modern Particle Physics. I' having a hard time understanding the last step in this calculation: The relativistic energy-momentum relation is $E^2 = m^2 ...
-1
votes
0answers
20 views

Laser kinematics [closed]

The laser emitting a collimated (narrow) beam of light rotates with respect to the axis perpendicular to the emitted beam, performing N revolutions per second. The length A screen on which the laser ...
1
vote
3answers
57 views

Similar Triangles in $ a=\frac{v^2}{r}$ derivation

Looking at this image, it is said that the two triangles are similar. How are they similar? I can't seem to figure it out. I understand that they're both isosceles triangles, but how can I prove ...
0
votes
2answers
57 views

How does centripetal acceleration have direction/vector and magnitude while in the formula $v^2=v\cdot v$ is scalar?

$$a_c=v^2/r$$ 1. How does centripetal acceleration have direction or vector while in the formula dot product between velocity vector is scalar (as in kinetic energy)? Radius is scalar quantity. What ...
0
votes
1answer
77 views

Relativistic collisions (elastic) - stationary target, equal mass [closed]

I believe it is more of a conceptual question than a homework question. A moving electron with energy $E$ hits a stationary electron. Question is to find the scattering angle (the angle between the ...
0
votes
0answers
18 views

Theorem of relative derivatives, Mozzi Equations and Theorem of relative motion

I am currently studying Kinematics in a Mechanics course and I am unable to find sources besides college material to help me studying what I learn in classes, probably due to my ignorance regarding ...
0
votes
1answer
41 views

In the equation for acceleration (with known $v$, $u$ and $s$) why velocity is squared and displacement is multiplied by 2? [closed]

In the following equation $$a = \frac{v^2 − u^2 } {2s} ,$$ where $v$ is the final velocity, $u$ is the initial velocity, and $s$ is displacement. Why is velocity squared and displacement multiplied by ...
0
votes
2answers
34 views

Intuition for formula of tangential component of acceleration in general curvillinear motion

In certain problems of plane motion, the position of the particle P is defined by its polar coordinates $r$ and $\theta$. It is then convenient to resolve the velocity and acceleration of the particle ...
2
votes
1answer
53 views

What is $mass \cdot jerk$, or yank?

So if Momentum is $m \cdot v$, Force is $m \cdot a$, and Jerk is $\frac{\Delta a}{\Delta t}$ what is $m \cdot j$? I've read that the name for this is yank, but I'm curious as to what it is ...
-1
votes
1answer
42 views

Why $g$ on equator is less than $g$ on poles? [duplicate]

I found this on my physics book. The book says $g$ on equator 9.78 $m/s^2$ and on the poles 9.81 $m/s^2$. Is it due to gravity?
-1
votes
2answers
44 views

What is the difference between velocity and speed? [duplicate]

What is the difference between velocity and speed? could anyone describe it more specific? does velocity have direction?
0
votes
1answer
49 views

When a body completes one revolution around a circular path will its acceleration be 0?

When a body is moving in a circular motion the acceleration keeps changing, will it be zero when it comes back to the same point it started from(will the average acceleration be 0?)
0
votes
1answer
44 views

Four momentum squared and collisions

So, I am not asking is the square of four-momentum of a particle an invariant to Lorentz trasnformations, but rather,is it invariant in dynamic situations? It seems to me that this also has to hold. ...
0
votes
0answers
40 views

Acceleration as the second derivative of displacement function

Let $x$ be displacement as a function of time $t$ and some other physical quantity $k$ such that $ x = f(t,k) $ Now, 1) Will the acceleration $a$ be $\frac{\partial^2 x}{\partial t^2}$ or $\frac{d^...
-1
votes
3answers
55 views

Can a person free fall onto a big block of jelly and survive disregarding the eventual suffocation? [closed]

Assuming the height is sufficient enough to achieve terminal velocity how high should the block of soft jelly be to dissipate the impact energy safely for an average human?
-1
votes
0answers
22 views

Solving simultaneous equations for motion [migrated]

Textbook asked student to solve the following simultaneous equations where x is distance in cm and t is time in minutes: x = 2t x = -4t -20 I multiplied equation 1 by the 't' coefficient of ...
1
vote
2answers
31 views

How do I determine the components of a cinematic jump, for vertical and horizontal velocity?

I have been tasked with determining the feasibility of The Rock's jump in the movie 'Skyscraper' I am using projectile motion equations to determine it, but have gotten stuck whilst calculating my ...
0
votes
6answers
470 views

Confusion over units in force equation? [duplicate]

While discussing Newton's laws, our book says Force is proportional to rate of change of momentum so they say F is proportional to mass * acceleration if mass is constant So $F=kma$ where $k$ ...
6
votes
2answers
135 views

Do free particles slow down in expanding universe?

My favorite toy model of cosmic microwave background in the expanding universe is a cube with totally reflective walls. If CMB is a black-body radiation, it must be isotropic and homogeneous - the ...
-2
votes
1answer
50 views

Why speed is defined as distance over time [duplicate]

Why speed was defined as distance over time ? Are there possible ways to define speed like distance plus time or distance minus time or distance times time
0
votes
1answer
51 views

Relative velocity of a thrown object w.r.t. ground [closed]

An old-fashioned coke bottle is thrown straight out from the right side of a car at 10 m/s. The car is moving at 80 miles per hour. What is the speed of the bottle relative to the ground (in m/s)? I'...
4
votes
2answers
106 views

Denoting the antiderivative of velocity

With simple Newtonian laws (and in a specific context), I learned that the speed $\vec{v}$ of an object is the derivative of the corresponding position vector $\vec{OM}$. So that means that $$\vec{v}(...
0
votes
1answer
32 views

How was the equation for a gravitational assist derived?

Im currently writing a paper about a hypothetical probe meant to escape our solar system and I want to analyse how gravitational assists would be beneficial for its mission. I found a website with an ...
0
votes
1answer
35 views

How to draw diagrams of Path, velocity and time for a complex problem?

What does an approach or a solution strategy look like for the following problem: Two point-shaped bodies with the masses m_1=100g and m_2=200g are connected to a string of 30 cm length and lie on a ...
3
votes
2answers
309 views

If an object in uniform motion with zero net force, can its mass change?

According to newton laws if something is in uniform motion and equivalent force is equal to zero then its mass cannot change. Our book says an object stays in state of rest or motion unless compelled ...
1
vote
2answers
67 views

Why does wave keep on travelling despite destructive interference?

I've problem here. Imagine you've a line of spheres that are attached to each other with springs. You push one sphere down hard. it drags its neighbors down and which in turn pull their neighbors and ...
0
votes
0answers
95 views

Angular velocity of rigidly rotating orbit in 3D

Consider a circle in 3-dimensional space. On this circular orbit, a rigid bead moves, thus changing its angle $\phi$ with a reference radius on the circle. The intrinsic angular velocity is given by ...
0
votes
1answer
23 views

How to chose which formula to use for thermal energy?

In some cases we use (3/2)kt in some cases kt and some cases (1/2)kt. How to chose which formula to use for thermal energy?
1
vote
1answer
36 views

Antiproton production threshold

Why is the antiproton threshold on cern 6* m_p and on uspas it is 7 * m_p?
1
vote
1answer
26 views

Angular acceleration of a double compound pendulum [closed]

How can I calculate the angular acceleration of a double compound pendulum? I'd like to know what the angular acceleration of each of the pendulum's center of mass will face at any point in time. PS -...
1
vote
0answers
63 views

Transformation of $4-$velocity

Notation: a greek index indicates four labels; spacetime coordinates $\mu = (0,1,2,3)$. A latin index indicates three labels; spatial coordinates $i = (1,2,3)$. $$* * *$$ A quantity, to be ...
1
vote
0answers
51 views

Does the proper four-acceleration $A^{\mu} = (0,0)?$

Let the proper four-position vector $x^{\mu}(\tau) = (0, \tau)$. Differentiating this successively wrt $\tau$ I get the four-velocity $u^{\mu}(\tau) = (0, 1)$ and then the four-acceleration $A^{\mu}(\...
0
votes
0answers
31 views

Confusion about valid set of virtual displacement

The answer of the problem below makes me confused about my thinking about virtual displacement... Consider the system in the figure below, similar to mechanisms used for aerial filming of sporting ...
1
vote
2answers
151 views

Locus equation of a projectile in terms of $\tan\theta$

This is the locus equation of a projectile projected from the ground at an angle $\theta$, with an initial velocity $u$ : $$ y = x\tan\theta - \frac{gx^2}{2u^2\cos^2\theta} \tag{1} $$ I just read ...
0
votes
2answers
48 views

Can the world line of a particle be successively differentiated to any order to always give a four-vector?

Starting with the world line of a particle given by $x^{\mu}$, this can be successively differentiated with the particle's proper time $\tau$ to give the four-velocity from the four-position, four-...
1
vote
0answers
38 views

Particles colliding at greatest height [closed]

Could I please ask for advice on the following question? It's the very last part. Surely it is wrongly printed because $(\sqrt3-1)(\sqrt3+1)=2$ And coefficient of restitution (e = separation ...
0
votes
1answer
58 views

Entropy production, local thermodynamic equilibrium and adiabatic process

It is said that for local thermodynamic equilibrium the local entropy production needs to be 0. Now, I am reading the following from the book by de Groot and Mazur "Non-Equilibrium Thermodynamics". ...
0
votes
2answers
59 views

$v_y$ vs $v_x$ curve, getting weird value of $v_y$ at $x$ = $0$

(I know the title isn’t clear. I didn’t know how to best describe my question in the title) So, we have a position-time relation : $\vec r$ = $2t\hat i$ + $4t^2\hat j$ It shows that the particle ...
2
votes
2answers
70 views

Can we know whether it’s a $1D$ or a $2D$ motion just by looking at the position-time relation?

How do I know whether it is a $2D$ or a $1D$ motion, just by looking at position-time, or velocity-time, or acceleration-time equations? Maybe the question is not very clear, I’m not sure I’m ...