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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1answer
29 views

How would the graph look like? [closed]

How do i sketch a graph of Kinetic Energy vs. Mass provided that momentum is constant? Pretty sure this is a basic question but i and my classmates can't get to a solution
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Solving an infinitely decaying propelling system [closed]

I am a HK secondary school student who is taking part in the HKPhO training in my school. I was doing some training questions and struggled with this question: A car with initial speed $v_0$ is ...
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Meaning of negative time

Whenever we graph time along a $x$-axis, we graph it along negative and positive $x$-axis both. So what does a negative time mean in the negative case axis? What does the negative sign indicate?
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Finding velocity from total linear acceleration

I am new to this platform so I apologize if I am asking question in an incorrect manner I am not a physic student hence the reason I am here to clarify some of my doubts. I have this idea of using an ...
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2answers
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Approximating the angle between the trajectory [closed]

I started to learn physics this semester and I found the following task: A contestant is participating in a half-maraton tournament(straight line length $L =21095$ meter) running in a zig-zag manner (...
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1answer
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Basic kinematics task with falling point equation [closed]

Suppose the equation of falling point has form of: $$ \frac{dv}{dt} = g - kv^2 $$ Calculate the terminal velocity Determine the relation between time and velocity I'm taking an introduction to ...
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Does it take more force to travel up the stairs or to travel up the slope next to it? [closed]

The answer might depend on numerous factors (steepness of steps, steepness of stairs etc.) Consider the length of the stairs and slope equal.
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3answers
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How can the SUVAT equations be derived from Newton’s laws of motion?

I would argue that the SUVAT equations, which correctly describe all constant-acceleration motion (including hypothetical situations governed by unusual laws of dynamics), cannot possibly be derived ...
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1answer
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Relativistic free fall

if I wanted to calculate how far a proton moving at horizontal speed of $0,96 c$ would fall (due to gravity $g$ vertically) passing through a space of $1$m (horizontally) - how do I calculate that? Do ...
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Radius of curvature of a particle with respect to another

A question requires you to find the radius of curvature of a particle with respect to another at a specific instant; the position vectors of both particles(varying with time) are also provided. The ...
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2answers
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Find final velocity of an object on an inclined plane without knowing the mass [closed]

How do I find final velocity of an object on an inclined plane without knowing the mass of the object assuming that I have the degree, duration, and initial velocity? Without the mass, how can I solve ...
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1answer
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Average and Instantaneous Acceleration [closed]

This example comes in my Physics book, but I don’t understand one part of the equation. The velocity of a particle moving along the $x$ axis varies according to the expression $Vx = 40 - 5t^2$, where $...
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How do magnetic fields due to random motions of charges cancel out in a current-carrying wire?

In my physics textbook, it states that magnetic fields due to random motions of charges cancel out at every point I know there's a drift velocity due to force imposed by the electric field, but the ...
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Does Zeno's Paradox hold the simplest key to explain the widely-held continuous spacetime belief in physics? [closed]

Richard Feynman in this 60's public lecture claimed it's easy to prove "physical space cannot be discrete automata", otherwise it will soon violate existing physical observations towards the ...
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Where must one use $x=A \cos \omega t$ and $x=A \sin \omega t$? [duplicate]

Consider the following example: A particle oscillates with simple harmonic motion in a straight line. In the first $t$ seconds, it travels a distance $a$. In the next $t$ seconds, it travels an ...
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Newton's $1$st law question

A long time since I posted it, still did not get a satisfactory solution. So I restate the problem - Why does not an object attached to a string which is attached to the roof of an accelerating bus ...
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Could Candide Thovex have avoided a crash by maximizing vertical air resistance?

NOTE: This is a very "practical" question and involves quite a lot of estimation. I'm sorry if this is the wrong place to post this question. If it is, please comment where I could post it ...
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Is there a limit to $\frac{d^nx}{dt^n}$? [duplicate]

There is already a question on the limit of acceleration($\frac{d^2x}{dt^2}$) and we all know the limit of velocity($\frac{dx}{dt}$) which is $c$ or the speed of light. My question is a generalized ...
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Why position of an object is unique?

Position in physics is defined as the location of an object w.r.t some reference point. I conceptualized it as the description of the path from the reference point to the location of the object. My ...
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Velocity Time graph [closed]

I'm trying to help someone with their A level maths and I'm perplexed by this question. A car starts from rest at time $t=0\,\rm s$. It accelerates uniformly until its speed reaches $V\, \rm{m/s}$. ...
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1answer
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Confused about linear displacement in circular motion

We know that velocity is the derivative of displacement w.r.t. time. Keeping this mind, suppose that we are traveling across a circle where we go from point A to point B. In textbooks, it is said that ...
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1answer
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Plot velocity and acceleration in Matlab\Octave knowing that $v(t)=\frac{t}{t^2+1}$ [closed]

An object of mass $m$ is observed moving along a straight line parallel to the $Ox$ axis. The scalar component of the object's velocity is given as a function of time by $\frac{t}{(t^2+1)}$, where t ...
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1answer
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How to calculate constant acceleration required to move an object by a distance $d$ in time $t$? [closed]

I’m working on an animation software and I require objects to have a downward acceleration. They currently fall at a constant velocity but I want to make them accelerate to make the animation look ...
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12answers
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Fourth Equation of Motion

When I was studying motion, my teacher asked us to derive the equations of motion. I too ended up deriving the fourth equation of motion, but my teacher said this is not an equation. Is this ...
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2answers
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Position of a charged particle in a radial electric field

I am trying to work out the radial position of a charged particle in an attractive radial electric field due to a fixed point charge. The acceleration of the particle is C/(r^2) where C is a const and ...
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1answer
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Accelerating a spaceship to near speed of light

Hypothetically, suppose we have the ability to accelerate a spaceship to near speed of light (lets say 0.9c). From what I remember of relativistic kinematics, the energy required to accelerate the ...
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Upper bounds on phase space momenta

Suppose I wish to calculate the phase space volume for the process $\overline{X}X \to A_1 A_2 A_3 A_4 A_5$ in the CM frame of $\overline{X}, X$ so that $\sqrt{s} = 2m_X$. The volume is given by $$ V \...
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Dark matter thermally averaged cross section

I'm trying to rederive the results of this classic paper: https://doi.org/10.1016/0550-3213(91)90438-4 to find the thermally averaged cross-section. I am struggling with a change of variables and ...
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1answer
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What does $AB$ mean in the paper On the Electrodynamics of Moving Bodies?

When reading through the paper "On the Electrodynamics of Moving Bodies" by Albert Einstein, my friends and I were confused by some of the notation used and how to interpret it. On page 3, ...
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1answer
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Determining charge magnitude through comparison with force of tension

Three charges of mass $m$ and charge $q$ are tied to massless ropes of length $l_!$, and hung from a single, fixed point. At equilibrium, the charges form an equilateral triangle in a horizontal plane ...
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1answer
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Particle paths - the distance moved by a particle in a velocity field

This question is is context to particle paths. Particle paths are trajectories of a given particle in the velocity field: $$\boldsymbol{u}(\boldsymbol{x},t)$$ A particle location at position $\...
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1answer
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Distance calculation without knowing time [closed]

I’m studying physics and am struggling to work out the correct formula for the below example question. Any help and explanation would be amazing. A tourist being chased by a bear is running in a ...
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1answer
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Question about circular motion and energy conservation

If we consider a ball attached to a string that moves in a circle at a constant speed, then in a ball-Earth system: the kinetic energy doesn't change, the string does zero work, and yet the ...
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1answer
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Kinetic energy produced in an explosion

If there is a train moving at 2 m/s with a cannon attached to it loaded with a ball, and then the ball is launched from the train, how would one find the kinetic energy produced by the explosion if ...
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1answer
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What's the speed of the train with our point of reference being the person who's moving inside the train? [closed]

A person moving in a train with the speed of 1m/s to the right, while the train is moving in the same direction with the speed of 10m/s From the person's point of view "considering that the ...
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1answer
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Where is the direction of acceleration in a body moving in 1 dimension? [closed]

like where is the direction of acceleration if a car is moving in a straight line or if an object is thrown upwards (its direction if acceleration) ?
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1answer
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How do I apply the principle of conservation of angular momentum in this case?

I came across a question: A disc of mass 2M and radius R lying in a vertical plane which is free to rotate about a fixed horizontal axis passing from its centre. A particle of mass M is tied to a ...
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1answer
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Does two objects are moving at the same time with the same acceleration, have the same distance travelled?

If two objects are moving at the same time with the same acceleration, would they have the same distance travelled? I used this formula to explain that it depends on the initial velocity of the ...
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2answers
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Acceleration is given in terms of position then it has been asked to find the position at time t

The question is as follows : The acceleration $a$ of a particle is given as $a(x) = x$ where $x$ is the position of the object on the $x$-axis. Then find the position of the object in terms of time $...
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1answer
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Showing a system is in Simple Harmonic Motion [closed]

A force of $F=(8-2x)$ is applied to a $2kg$ object in the $X$-direction. It is released from $6m$ away from the $x=0$ point. Show that the object is in a Simple Harmonic Motion. And derive a formula ...
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1answer
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Need help interpreting Displacement time graphs

In this image is a displacement-time graph of the movement of an iguana. Within the video (Khan academy), the explanation is that between 0 and 5 seconds, the displacement of the iguana is Xfinal-...
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3answers
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Average velocity derivation [closed]

Most of the time we make a mistake when calculating average velocity where $$\bar v'=\frac {\sum v} n$$ but the actual is $\bar v=\frac {\sum s} {\sum t}$, can we use the wrong to get the correct ones?...
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1answer
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Elegant way to find maximum range of a projectile launched from a height

A projectile is launched from a height of $h$ and the initial velocity of $\sqrt{2ga}$. Find the maximum range achieved by the projectile in terms of $g$,$a$, and $h$. I can go about the traditional ...
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2answers
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Can I assume a uniform motion to be a rotation for a point in time? [closed]

Can I assume a uniform motion of a point mass with velocity $v$ for a point in time to be a rotation around a point $P$ that has a distance $r$ to the point mass, so that the angular velocity of it ...
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1answer
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How to solve a general form of a homework question: [closed]

First of all the original question is from Halliday Fundamentals of Physics book. Figure 2-24 shows a general situation in which a stream of people attempt to escape through an exit door that turns ...
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1answer
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Minimizing travel time of a car given some confusing constraints

I came across a fairly basic kinematics question in the first chapter of "An Introduction to Mechanics, 2nd Edition" by Kleppner & Kolenkow: "A sportscar, Electro-Fiasco I, can ...
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1answer
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Initial conditions of transient behavior of a driven oscillation

For a driven oscillation $$X_G = A_0e^{-\frac{\gamma}{2}t} cos(\omega_v t + \phi) + A cos(\omega_d t - \delta),$$ where $A_0$ and $\phi$ are determined by the initial conditions $x_0$ and $\dot x_0$ ...
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2answers
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Estimation of greatest speed in a polyhedron

in order to control velocities in a three dimensional volume, I look for a proof or a proof idea for the following assumption: Given a non-empty solid polyhedron in 3D, all points inside this set ...
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1answer
37 views

Can the acceleration of a decelerating particle be positive? [closed]

let's say you have friction on a surface that makes particle A decelerate constantly at $-0.75 ms^{-2}$. when you draw a velocity-time graph to graph this you will get a line $y=mx+c$ with a negative ...
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0answers
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Is this intuition correct? (dot product)

So, it is based on the article below: Go to the bottom of the article where the 'Mario-Kart Speed Boost' example is. So, the intuition in the examples makes sense to me but sometimes people explain ...

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