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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Possible trajectory of a constant accelaration object

What is the possible geometrical shapes of constant acceleration object's trajectory ? Thanks for all.
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A car travelling along a straight road is leaking oil. What is the acceleration of the car? [closed]

A car travelling along a straight road is leaking oil. Drops of oil fall on to the road leaving the pattern shown in the diagram. The time between each successive drop is 2 seconds. What is the ...
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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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FInal velocity of object on an inclined plane given angle, time, initial velocity [closed]

A sled starts from rest, and slides down at 38.0 degrees frictionless hill for 4.24 s. How fast is it going at the end in m/s? How did you solve it? Thanks!
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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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An object moving along the $x$-axis according to the equation: [closed]

An object moves along the x axis according to the equation x = (3.00 m/s^3) t^3- (2.00 m/s^2) t^2- (4.00 m/s) t + 5.00 m , where x is in meters and t is in seconds. (a) Determine the x position of the ...
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Plot velocity and acceleration in Matlab\Octave knowing that $v(t)=\frac{t}{t^2+1}$

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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How to calculate constant acceleration required to move an object by a distance $d$ in time $t$?

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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Need Help with Physics Problem! [closed]

I got this problem while practicing and I need help with it! A fighter, traveling at 443 m/s fires a bullet at an angle 12◦ from the perpendicular toward the front of the plane. The muzzle velocity ...
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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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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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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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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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Kinematics in one dimension - interpreting answers [closed]

In the question below for b (i) - I get two answers: 6 seconds and 18 seconds. The answer of 6 seconds is correct (according to the answer sheet) but I can't interpret where the second answer is ...
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Speed in a friction medium [duplicate]

If a 20 kg object dropped in air has a terminal speed of 60 m/s, what was its acceleration at 30 m/s? I want the answer in steps
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Vertival motion [closed]

a ball A dropped from a height of 80m above the ground another ball B dropped from a different height 2 seconds after ball A dropped. if both strike the ground at the same time. what is the height of ...
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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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Does car push a broken down car exert a force on it if both are travelling at the same crusiing speed [closed]

If both bodies are travelling at a constant cruising speed, does that mean by Newton's First Law, they are not exerting a force on each other? Only when they're accelerating do they exert a force on ...
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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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1answer
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Is it possible to calculate height? [closed]

Background An object containing mass of $5$ kg fall on a surface and drowned $2.5$ m. Something similar when you throw a heavy ball from high up in the sky and the ball hits the sand in the sea-beach....
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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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The contradiction of the equation of motion of a free electron

I've been confused of the equation of motion of a free electron inside a conductor as a current flows. $\mathbf{v}:=$average velocity of free electrons inside the conductor. $\tau:=$relaxation time. $...
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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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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
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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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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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1answer
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Is there a word to describe when things are moving individually, but have a net velocity of zero?

I know this is a strange question, but I know there must be a word for it. So imagine a case where, taken as a whole, the net velocity of all particles equals zero, but each individual particle is ...
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3answers
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Does applying a force to keep a body in uniform motion not considered as a force because there is no acceleration. (Friction included) [closed]

Because I have studied that if there is no acceleration then there is no force.
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1answer
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Is the relation “slope=velocity” mathematically valid?

$\text{Slope= tan(angle with respect to positive X-axis)= scalar output}$ $\text{velocity= a vector }$ Source: Hugh D Young_ Roger A Freedman - University Physics with Modern Physics In SI Units (...
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2answers
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Why the formula of kinetic energy assumes that the object has started from an initial velocity of zero?

According to my physics textbook, the formula of kinetic energy is: $$ W = \frac{1}{2}mv^2 $$ Where $m$ is is mass of the object and $v$ is the velocity of the object. The equation is calculated from ...
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1answer
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What is the magnitude and direction of the change in velocity if the inital velocity is 30m/s south and the final velocity is 40m/s west? [closed]

I got the magnitude correct which is 50 m/s however I don't know how to solve for the direction of change. Any help?
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1answer
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How to calculate the time it takes two trains to stop after decelerating? [closed]

The problem statement is as follows: Two trains, each traveling at $30\,\mathrm{ft}/\mathrm{sec}$, approach each other on a straight track. When they are $1000$ feet apart, a bee begins flying from ...

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