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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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27 views

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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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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287 views

Acceleration of moving reference frame

I want to simulate the readings of an accelerometer that is arbitrarily moved through 3D space. In an inertial reference frame $W$, the motion of the accelerometer is described by it's linear ...
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How can the acceleration of a person on a zipline be calculated?

I was thinking one day about how a speed, or perhaps the acceleration, of a person riding a zip line could be calculated. I first started by thinking of an ellipse where the two foci were the anchors ...
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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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How to understand motion of waves through functions of two variables - time and distance?

$$ s(x,t)= A \sin(\frac{2\pi}{T}t-\frac{2\pi}{\lambda}x) $$ 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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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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How to find the initial speed on the y axis while only having $Dy$, $Dx$, angle, and acceleration? [on hold]

Is it possible to find the initial speed of a projectile on the y axis while only having $D_y$ (distance on the y axis), $D_x$ (distance on the x axis), the angle and $a_y$ (acceleration on the y axis)...
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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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1answer
42 views

Who will win the race?

There is a wedge which is inclined at an angle X to the horizontal.Supppose two carts of same mass M one having 3 wheels and the other having 4 wheels are released from rest at the top of the incline,...
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The acceleration needed to stop a car in time [on hold]

Say you are driving at the speed of 30 m/s, when suddenly a car in front of you, which was previously traveling at the same speed, brakes. If you press your brakes 0.455 s later, what would the ...
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How do you determine whether answer is A or D? [on hold]

How do you tell the difference between graphs A/D from t=0 to their maximum postions given this eqaution.
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Is Torricelli's law “wrong” for big holes? - Tank draining problem

Consider a tank full of water with a constant cross-sectional area A1 placed vertically on the ground. Now someone drills a hole of an area A2 in the bottom of the tank, and the liquid starts escaping ...
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Write Equations of motion and a phase portrait of a point particle [on hold]

A point particle with mass m = 1 moves along the X axis under the the force $f (x) = x^3 + x^4$. Write the equation of motion of the point and draw a phase portrait. What I have so far: So, $f = m\...
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How can momentum but not energy be conserved in an inelastic collision?

In inelastic collisions, kinetic energy changes, so the velocities of the objects also change. So how is momentum conserved in inelastic collisions?
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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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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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Converting velocity vector formula from Cartesian coordinate system to polar coordinate system

I have a little question about converting Velocity formula that is derived as, $$\vec{V}=\frac{d\vec{r}}{dt}=\frac{dx}{dt}\hat{x}+\frac{dy}{dt}\hat{y}+\frac{dz}{dt}\hat{z}$$ in Cartesian Coordinate ...
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Kinematics: Circular Motion

What is the difference between angular velocity and angular speed? Is angular velocity after one complete rotation zero? Is the magnitude of angular velocity always equal to angular speed?
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How do i calculate the speed of the ball? [on hold]

A spring pushes a 15 grams ball with 10 m/s in a bent pipe. What is the formula to calculate the speed of the ball in point A and point B. The pipe is horizontal so there is no g-force and the pipe ...
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Question is in description [on hold]

If a volleyball gets served at a height of 2ft at 15m/s from one side of a 60ft court over a 7ft net, what angles will make the ball travel the whole court exactly?
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Average acceleration [on hold]

The space shuttle Discovery has made 30 flights. The space shuttle is approximately 37 meters long and has a wing width of 24 meters. The three main engines of the space shuttle are used when ...
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Projectile landing at different elevation [on hold]

A ball is kicked at an angle of 30 degrees from the horizontal from point A and lands at Point B which is located 15 ft horizontally ahead and -9 ft vertically. There is also an equation provided, $y=-...
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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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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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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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Help With a Projectile Motion Problem [closed]

So I have what seems to be a fairly easy projectile motion problem that I just can't solve, I believe I am using the wrong idea and am requesting help! The problem is as follows: A boy on the edge ...
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I want to learn the behavior of rotating bodies thrown in the air [on hold]

Could anyone suggest me a paper that could help me on that? ( That describes it mathematically. )
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4answers
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If you are sitting completely still inside of a moving car are you at rest?

My teacher and I had an argument in class where I stated that motion is undefined without a reference point and that you could just as easily claim that the road is moving backwards at the opposite ...
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Projectile Motion

I know the angle at which a projectile is launched, how far it needs to go, and also the maximum height. How can I find the initial velocity needed (disregarding air resistance)? Currently, I am ...
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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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Why do these two ways of understanding constant acceleration give different results?

I have a question pertaining to the concept of acceleration and it's formula - Both seem to give me different answers. I was asked: A train is moving at a velocity of $20\ \mathrm{m/s}$. It hits ...
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What are two different angles we can throw a ball, so it lands at the same spot? [closed]

This is not a particularly difficult task, but it has given me a lot of trouble and I can't solve it. We throw a ball at 60° angle with a speed of 20 m/s. The ball lands 35.2 m away. What is the ...
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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 ...
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1answer
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kinematics: Angular velocity [closed]

What is angular velocity when an object rotates through half a revolution in clockwise direction and then rotates through half a revolution in counter clockwise direction to reach the final ...
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3answers
583 views

Average acceleration and centripetal acceleration

What is the difference between centripetal acceleration and average acceleration in this worked example? If $\frac{\Delta v}{\Delta t}=\frac{v^2}{r}$ and $v=3$ m/s change in time is $1$ second and $...
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What is the effect of acceleration due to gravity on horizontal acceleration?

The question is the following: An object accelerates from rest to $100\,\mathrm{km}$ per hour in $4.0\,\text{seconds}$. What fraction of the acceleration due to gravity is the car's acceleration? ...
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Finding initial velocity of balls [closed]

Ball A is released from rest at height h above the ground. At the same time, ball B is projected vertically upward with initial velocity u. After some time, two balls are at the same height above the ...
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1answer
222 views

Classical Relativity: Clarification

I am working on a problem that states: "A swimmer capable of swimming at a speed $c$ in still water is swimming in a stream in which the current is $u$ (which we assume to be less than $c$). ...
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How does relative motion theory adjust other variables than kinematics' basics like velocity or displacement?

I have been confused on this concept for a while - suppose a boy is going from east towards west with some velocity on a bicycle and rain is falling in a vertical downwards direction. Then, if we ...
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1answer
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How do you derive $v_f^2 = 2ad + v_i^2$ from $v_f = v_i + at$ and $d = v_it + (a/2)t^2$?

I'm trying to use substitution to find the equation Vf^2 = 2ad + Vi^2 from Vf = Vi + at and d = Vit + a/2(t^2), but I get stuck understanding part of the math. I've attached a picture, and you can see ...
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The instant an accelerating object has zero speed, is it speeding up, slowing down, or neither?

This problem is from Khan Academy. Specifically for the blue point circled in red, the answer is that at this blue point, the object is neither speeding up nor slowing down. When I think about the ...
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2answers
58 views

${}$ Kinematics: One dimensional motion [closed]

Above is the speed-time graph of a particle in motion along a constant positive direction, as per my textbook accelration in the interval 3 is positive. But I think acceleration in the interval 3 is ...
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2answers
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Velocity of a ball rebounding off a moving train

At the bottom of this page says (my emphasis): It's interesting to note the speeds in the cartoon. The propeller-beanie kid sees his tennis ball moving away from him at 30 miles per hour. So ...
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2answers
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Acceleration of a Bouncing ball when it hits the ground

The conceptual problem I am having difficulty with is something like this: If a bouncy ball is dropped from some height $h$ and rebounds to a height of $0.75h$ in some time $t$ (for example), what ...
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Does slope of $y$ vs $x$ curve tell anything about magnitude of instantaneous velocity at that point?

I know that slope at any point on the trajectory of a moving body gives us the direction of its instantaneous velocity. Does it tell us anything about magnitude of the velocity at that point? I don’...
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2answers
54 views

Kinematics: One dimensional motion

If a particle is moving in one dimension with constant speed, can we say acceleration is zero at all the points? Answer given in my textbook is yes acceleration is zero. But I think it can undergo a ...
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Any nice solutions to this kinematics problem? [closed]

So I made a mock F=ma exam with a couple of my friends on AoPS. Here is one of the problems (problem 21) Bob lives in the universe $\Omega$, which happens to be a physics simulation. In $\Omega$,...