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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Average velocity and instantaneous velocity

In some books of Physics in Italian language, they write that the instantaneous velocity $v$, is: $$v=\frac{dr}{dt}=\lim_{\Delta t \to 0} \frac{\Delta r}{\Delta t}$$ where $v_{\text{avg}}={\Delta r}/...
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How do we use the initial velocities to find the final velocity? The answer is 7.7m/s. Your help would be highly appreciated by me and my friends [on hold]

An astronaut on the moon, where there is no air resistance, throw a ball. The ball's initial velocity has a vertical component of 8.00 m/s and a horizontal component of 4.0 m/s. The acceleration of ...
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Average velocity with constant acceleration. Two formulae but different answers [on hold]

Data: t1 = 0, v1 = 5m/s, x1 = 0m; t2 = 2, v2 = 10 m/s, x2 = 20m; t3 = 4, v3 = 15 m/s, x3 = 60m Find the average velocity. First formula = 1/2 (vinital + vfinal) = 1/...
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Does the conservation of 3 and 4-momentum implies the conservation of relativistic energy?

In special relativity, we require 3-momentum, 4-momentum and energy to be conserved. This gives three equations. However, after solving some exercises on relativistic dynamics, I find that I usually ...
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Simple harmonic motion position and velocity

It is given that the acceleration of a particle is $a=a_0\sin(wt)$ and $v(0)=0.$ Therefore, $v=\frac{a_0}{\omega}-\frac{a_0}{\omega}\cos(\omega t) $ $x=\frac{a_0}{\omega}t-\frac{a_0}{\omega^2}\sin(\...
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Determining amount of distance $x (3m)$ traverses [on hold]

The pulley is pulled by $F$ force and traverses $a$ of an amount of distance. How much distance does object $x$ traverse? A) $4a/31$; B) $5a/31$; C) $6a/31$; D) $7a/31$; E) $8a/31$ (no ...
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Prove that the height swept by the ball in the last second is $5 m/s$ [on hold]

I was studying kinematics and came across the following observation: every ball thrown upward with a speed greater than or equal to $ 10m/s $ will travel 5m in the last second of movement to maximum ...
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How to calculate/use horizontal coefficient of restitution value for basketball?

I'm trying to run an experiment in which a basketball is dropped straight down with a certain angular speed and then undergoes a bounce. My goal is to create a relationship between the initial angular ...
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Angles of projectile motion [closed]

A soldier decided to hurl a ball of mass 40kg somewhere 400m away. If the maximum range is 500m, find the angles of projection. I can't seem to get my head around this one. I tried to find vertical ...
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Determine angle of propulsion [closed]

Fuel is burnt to propel the missile, if propulsion provides a constant acceleration of 40m/s, determine the angle that missile must be angled to make it fly at a constant height. Not sure what to do ...
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Generalization to Rear-Wheel Steering?

Given the position of the vehicle (𝑥,𝑦) at different time points, the speed of the vehicle (m/s), the direction the vehicle is facing (heading — in degrees), the track width of the vehicle, and the ...
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Related to the information contained in $a = v \frac {dv}{ds}$

While studying kinematics I came to the definition of acceleration which is $a = \frac {dv}{dt}$. But from this equation we can derive that $ a = v \frac {dv}{ds} $ which when I evaluate at $v=0ms^{-1}...
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How does the force on a crashing train relate to its velocity and the area of the train that is touching the wall?

I am modelling the crashing of a train with a deformable crumple zone on the front. I am assuming that the crumple zone deforms from the front back, so I am essentially modelling it as if the crumple ...
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4answers
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Acceleration-time graph for a falling object

I understand that when drawing an acceleration-time graph for a falling object (with initial velocity = 0), the y-intercept should be $9.81ms^{-2}$ and acceleration should end up being $0ms^{-2}$ as ...
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Distance traveled by a particle in $n^{th}$ second

My book states that the distance traveled by a particle thrown upward in the last second is independent of it's initial velocity because the the object travels the same distance as a freely falling ...
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Why is the normal force equal to zero at the top of a rollercoaster if the speed is the minimum?

I was practicing for one of my physics exams and there was a problem that asked for the minimum speed a rollercoaster would have to go for its riders to not fall out at the top of a loop. I did the ...
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When the direction of a movement changes, is the object at rest at some time?

The question I asked was disputed amongst XVIIe century physicists (at least before the invention of calculus). Reference: Spinoza, Principles of Descartes' philosophy ( Part II: Descartes' Physics, ...
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Moving an object which is at rest on the floor

A block for example, its net force would be $0$. I am imagining a scenario where I apply a vertical force such that $0<F<F_g$. The way I understand it is that this, theoretically, means that, ...
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1answer
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Does super position precede physical phenomena?

If a traveling wave has amplitude of d, it feels certain amount of force at that moment in time when it is displaced for equilibrium. Thus there is also strain on the string corresponding to that ...
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Kinematics and Acceleration Windows

I am a CS student who is currently programming for a robotics project. The kinematic physics at play has me a bit confused, and I am wondering if someone can provide some clarity on this problem: I ...
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The physics of board breaking

Pardon my really rusty school physics knowledge. I heard martial artists talking about the physics of board breaking and one of the things which they mentioned is formula "F=ma". They were talking ...
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Finding the distance traveled by a jet [closed]

QUESTION (The following question is from Physics NCERT, standard textbook in India) An aircraft is flying at a height of 3400 m above the ground. If the angle subtended at a ground observation ...
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Physical interpretation of complex numbers, part 2

I walk in the x direction, if I walk twice as fast, 2x, if I walk backwards, -x. What about ix? If I say that I walk an imaginary distance ix then this means in physics and maths that I walk ...
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How to prove the relativistic momentum?

As far as I know, the relativistic momentum of a particle is given by the equation: $$p=\frac{m_0v}{\sqrt{1-\frac{v^2}{c^2}}}$$ where $m_0$ is the mass of the particle and $v$ is the velocity of the ...
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Derivatives of polar coordiantes?

I'm a undergraduate and I was reading about the polar coordinate system specifically this paper. I don't understand the term: $$\frac{de_r}{d\theta} = e_\theta \text{, and } \frac{de_\theta}{d\theta}...
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Can an atom be simulated based on the current theories related to charge?

I am not speaking about using computer graphics to visualize a atom, but to actually take 2 balls and charge/neutralize them to simulate an atom.
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simulating partially inelastic collisions [duplicate]

I have an abstract problem that I am trying to wrap my head around. I understand that to solve the problem of the final velocities in a perfectly elastic collsion, you can determine it using the ...
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2answers
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Instantaneous Velocity at a Sharp Point

My friend and I are having an argument. Here's the situation: A block is at rest on a frictionless surface. At instant $t_0$ a person pushes the block to the right with a constant force. At instant ...
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Are both kinetic energy and momentum conserved when 2 objects undergo a collision? [duplicate]

for example when two objects undergo a collision and no external force is acting on them. Will both kinetic energy and momentum be conserved or just momentum?
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How much force is necessary for a crowded bus to get out of inertia

I have always wondered how much force is necessary for a crowded bus or train to speed from 0 km/h to 20 km/h, and compare it to some known figure, like a great white shark bite. This curiosity hits ...
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How do I interpret/make sense of $\frac{d\theta}{dt}$ in physics’ language?

Here’s a question from my textbook. It’s a simple question that involves a little bit of calculus. I was able to solve it. But what I don’t understand is, I could not fully understand the final result....
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Can momentum be considered as a measure of inertia of motion?

If inertia of motion is a body's tendency to be in motion then can momentum be considered as a measure to calculate that tendency to be in motion?
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1answer
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Physical Interpretation of an Elementary Inequality in Kinematics

I recently came across the following question: suppose a point mass moves a distance $d_1$ for $t_1$ seconds at a velocity $v_1$, then accelerates instantaneously to a velocity $v_2$ and travels a ...
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Where is information of motion stored?

I've asked variations of this question a few times to a few people. My physics professor answered it with: "if no forces act on an object why should it stop, start, or do anything else?" But that ...
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Displacement Vector

I am trying to understand how multiple dimensions will affect displacement. I'm given the initial velocity: $-2.5\frac{m}{s}\hat{\textbf{i}}$. The acceleration is: $3.5\frac{m}{s^2}\hat{\textbf{i}}...
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How to understand motion of waves through functions of two variables - time and distance? [closed]

$$ s(x,t)= A \sin(\frac{2\pi}{T}t-\frac{2\pi}{\lambda}x) $$ Basically I would love to get some plausible and thorough explanation of plotting these two independent variables in order to satisfy the ...
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2answers
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Difference between displacement-time graph and position-time graph

While going through my physics book, I got over a question which ask us to plot a position-time graph for the interval ($t=0\,\mathrm s$ to $t=5\,\mathrm s$) From the top of a tower, a ball is ...
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1answer
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Given acceleration, why must kinematics be used when solving for distance in terms of time rather than the literal definition of acceleration?

I'm working with rotational motion, and one of the mistakes that I made in solving for distance in terms of time was substituting angular acceleration for (d/Rt^2) where d is distance and R is the ...
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4answers
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Can motion be considered a dimension?

Okay, go easy on me, I’m in no way any kind of physicist, or even a scientist, I graduated High School and that’s it, but I do have a very mechanically based mind, (probably why I wound up a Diesel ...
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Having some trouble with acceleration in polar coordinates

So, I solved a question about acceleration in polar coordinates, but most people in my class (Classical Physics, first year at university studying Physics) disagree with my answer. So the question is ...
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Frame of Reference in Kinematics

If we have two frames of reference, say S1 and S2, and the acceleration of a particle as seen from both the frames has equal magnitude, say 4 m/s^2, then shouldn't the frames have no relative ...
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1answer
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Stanley kinematic model controller

I am having problem calculating delta (steering angle). L is the length of vehicle lfw is distance between rear and center of vehicle. eta is the angle between direction of the vehicle and target on ...
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1answer
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Finding the average speed plus a break [closed]

I have the following equation when the driver drove 2.5h at 120 km/h and then stopped for 30 minutes. Then he drove for 20 minutes at 25 m/s. The result of the equation is to determine the average ...
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1answer
51 views

Direction of acceleration vector at the apex of a curve

(Test Your Understanding of Section 3.2) The question wants me to choose the correct acceleration vector, from the given 9 options where 9th option is zero acceleration. Ok, first I thought option ...
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From the frame of reference of a colliding object, does the entire universe change direction when it bounces?

Consider three objects: a rubber ball, a spaceship, and an isolated brick wall floating serenely in the vacuum of space. From the perspective of an observer on the spaceship, the ball is moving ...
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Is there any physical evidence for motion?

Let's say that we have 2 tennis balls in space, one being in motion (say, pushed by an astronaut), and the other one still. If we could take a snapshot of both tennis balls, would there be any ...
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1answer
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The velocity of an object leaving the inclined plane

I saw the question below in our physics textbook. It asks A block of mass m is released and slides down on the frictionless inclined surface ( the inclined plane is of concrete and doesn't ...
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Energy spectrum of photoneutrons

In "Radiation Detection and Measurement" Knoll considers the production of neutrons by a ($\gamma$, n) reaction such as \begin{align} \gamma + \ ^{2}_{1}\text{H} \rightarrow \ ^{1}_{1}\text{H} + n &...
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1answer
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Tangential velocity after ball strikes wall

I have to solve a problem where there is a ball that goes in the perpendicular direction towards a wall. It strikes the wall and goes back at the same angle it came from. (All the movement are ...