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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30 views

Elasticity of spring and conservation of energy

I have a problem of one of my students mechanics homework that I am unsure on and could do with resolving by tomorrow is possible! A spring of natural length $0.5m$ is attached to the ceiling and a ...
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The Bird Flight is Observed [closed]

The path of a bird flight is observed. The bird flies in vertical plane with a constant vertical acceleration of $8 \frac{m}{s^2}$ downward. When observation begin, the bird is in flight at a height $...
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How to draw resultant Vector for this question [closed]

A boat is moving with velocity of 3i 4j in river and water is moving with a velocity of -3i -4j with respect to ground. Relative velocity of boat with respect to water is : I am not getting is how to ...
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Question regarding relative velocity of muzzle bullet? [closed]

A police jeep is chasing with, velocity of 45 km/h a thief in another jeep moving with velocity 153 km/h. Police fires a bullet with muzzle velocity of 180 m/s. The velocity it will strike the car of ...
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Computing the distance where two solids reach each other using basic speed formula (high school problem) [closed]

A car$B$ which moves in a straight line at a speed of $50km/h$ arrives at a point$B$ ($d_{B}$) on the line, and a car $A$ which moves in the same straight line at a speed of $100km/h$ reach the point$...
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Basic high school physics problem regarding the formula speed is the distance over time [closed]

A train 1 moves from a point $A$ in straight line at $38 km / h$ and after $2.5$ hours is followed by a train 2 which moves from the same point $A$ in straight line at $80$ km per hour. At which time ...
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Velocity of point of intersection of 2 rods [closed]

I'm not getting how are we getting u greater than c for part b by using formula for part a. Plz explain
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Angular velocity to linear velocity Modern Robotics textbook

In the second to last sentence, I have no idea how $v = (2,0)$ was calculated. Can someone derive this for me in detail, or with a picture?
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Why does the bottommost point of a rolling body have a radial acceleration in the ground frame?

Let's say a solid cylinder of radius r is rolling on a stationary horizontal surface with linear velocity v, angular velocity $\omega$, linear acceleration a and angular acceleration $\alpha$ Bottom ...
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1answer
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Simple physics question pls help [closed]

If two balls, A and B are projected with an angle from the same level but both reach same maximum height. The angle that Ball B makes with the horizontal line is greater than the angle that Ball A ...
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Is there a way to solve this question using instantaneous center method? [closed]

This question is about instantaneous center method of finding velocities. I saw this question on a exam paper, but i think the question may be wrong because i couldn't find a way to get IC(1,3) Or ...
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1answer
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What is the acceleration-time graph for a bouncing body? [closed]

So suppose a ball is dropped from a point above the ground. Taking the point from where the ball is dropped to be the initial starting position, what would be the acceleration time graph of the ball. (...
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1answer
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Are superconductors primarily for DC transmission?

I understand Superconductors can be beneficial due to their resistance to magnetic fields as in levitating bullet trains or MRI machines, but is our main interest for DC power distribution? I see ...
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What is the trajectory motion analysis in below question? [closed]

After being kicked by a footballer, a ball started to fly straight towards the goal at velocity v=25 m/s making an angle α=arccos0.8 with the horizontal. Due to side wind blowing at u=10 m/s ...
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1answer
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Why is direction of train like this for car?

This is an image of a train and a car. T is the train moving towards - $x$ axis and C is the car moving towards $+ y$axis. So, my teacher made a resultant velocity with $-5\hat i$ and $-20\hat j$. ...
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What will happen to the ball in a vacuum container when suddenly the gravity after 2 seconds disappears? [closed]

Suppose that there is a ball in a vacuum container where mass of the ball is $2$ kg. The height of the container is $100$ m. Assume that the acceleration due to gravity is $10$ m per second square. I ...
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Is this correct regarding velocity of train?

So many yellow T drawn are just different position of train at different instants.The person is standing still at all those instants at one place. If a train is moving at 5m/s. Then for me , can we ...
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1answer
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Direction of $V_RM$ confusion

So ,please read both the questions . They have similar originate questions that I am facing difficult in. Let us say rain is falling downwards with v = -5j and a man is moving with a velocity of 2i in ...
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3answers
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Tension of string suspending a ball in Circular motion, given the mass of ball, radius and length of string [closed]

Ok so I have this question where a ball is suspended by an inextensible string and is caused to rotate in a horizontal circle which has its centre vertically below the point of suspension. What would ...
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Confusion in relative velocity with rain man problems

My major conceptual difficulty in understand this concept is mostly the direction of velocity of man with respect to rain. Let us say rain is falling downwards with v = -5j and a man is moving with a ...
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2answers
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Does the SUVAT equations of motion (Kinematics) come from some differential equation?

Wikipedia says about the equations of motion that; "If the dynamics of a system is known, the equations are the solutions for the differential equations describing the motion of the dynamics.&...
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Why the direction of the omega (angular velocity vector) is along the axis of rotation? Also for angular acceleration

I know that the direction of omega is taken along the axis of rotation but I don't understand it why it is taken? I also know that $\mathbf v = \mathbf ω \times \mathbf r$ so, all three vectors ...
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3answers
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Calculating displacement from acceleration (intuitively) [closed]

If I say acceleration of car is constant at $4\; \rm m/s^2$. Then isn’t it that it covers $4\; \rm m$ in $1\; \rm s$ with velocity $4\; \rm m/s$. Then in $2\; \rm s$, the velocity is $8\; \rm m/s$. ...
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1answer
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Simple pendulum with moving support in a parabola

The problem says that I have to find the equations of motion in the Hamiltonian formulation for a simple pendulum with mass $m$ and lenght $l$, which its support moves with no friction along the ...
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Change in kinetic energy in inelastic collisions [closed]

My question is "Which of the inelastic collisions will cause a greater change in Kinetic Energy?" 1: When a moving large-mass hits a stationary small-mass body 2: or when a moving small-mass ...
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What happens to the momentum of this rainfall? Are these expressions describing the rainfall correct/significant?

An element of mass $\Delta m_r$ (mass of rainfall) falls vertically onto a mass $m_c$ (a cart). The empty cart starts from rest and there is no friction. A constant horizontal force $F = <F, 0>$ ...
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Is it ever possible to have zero motion but non-zero acceleration? [duplicate]

First of all , here is a definition of motion I found in Wikipedia: In physics, motion is the phenomenon in which an object changes its position over time. Motion is mathematically described in terms ...
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Anyone know how to find stopping time [closed]

Determine the Stopping Times What would your stopping times be for each of your speeds from the “Stopping Distance Lab”? Think about what you have vs. don’t have. We ultimately need time but how do ...
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How to use equation of motion like this here? [closed]

So I will explain my problem exactly what it is.Please do answer in such a format by telling me places where I am wrong from the text I write.I posted this question earlier also but I noticed many of ...
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3answers
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Confusion in equation of integration and differentiation for motion?

It says displacement time equation here but x is position of particle here I think. It is not displacement of particle here. But when it is given velocity of particle to us and then we integrate it. ...
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Why quantities in physics are always talking about rates? [closed]

I get the idea that physics wishes to study changes to discover new rules. But why is everything related to rates? Acceleration,Velocity? Could we use something else apart from these? What can you ...
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4answers
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Why does a body falling down follow this pattern of velocity?

I was wondering about the pattern of velocity for a body falling down with initial velocity $u= 0$ and $g = 10m/s^2$. Without using the formula , I thought : Velocity would change in this manner (...
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1answer
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Question of ball falling down.Difficulty in understanding the formula

A ball is thrown upward from the top of a tower 40m high. u = 10m/s.Find time for it reach AD. g = $10m/s^2$. Taking upwards direction as +ve and downward as -ve. u = +10m/s.$g=-10m/s^2$.s=-40. $-40 = ...
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Difficult in understanding question of minimum stopping distance [duplicate]

A car moving with a speed of 40 km / h can be stopped by applying brakes after at least 2 m. If the same car is moving with a speed of 80 km / h, what is the minimum stopping distance. As I have ...
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1answer
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One-dimensional harmonic move - input parameter conversion

I have one-dimensional harmonic move, but velocity is defined as function of distance from the beginning V(x) = (Vmax + Vmin)/2 + (Vmax - Vmin)/2 * cos((2 * PI / K ) * x ) Where Vmax > Vmin, Vmin &...
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Finding the velocity of a projectile thrown from a raised platform at an angle [closed]

The following question has been giving me trouble for a while now, it states A particle is thrown with speed $10 \space \text{ms}^{-1}$ from a point $2\space \text{m}$ from the ground, at an angle ...
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3answers
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What axes are typically used to graph projectile motion?

I am currently trying to model a function for the 2d projectile motion of a football from the angle of elevation and the initial speed, however I am a bit confused on what the graph of projectile ...
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Why is constant velocity of a body one-dimensional motion?

If velocity of a particle is constant. It is in uniform motion. Why is it that it is a example of one-dimensional motion? It can still change its direction and have constant velocity. By saying one-...
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Why don’t we consider angle 90 and 180 as angle made by acceleration

It states that angle made by acceleration when is between 0 and 89 degrees , acceleration increases whereas in case when it is between 90 - 179 degrees, acceleration decreases. I didn’t understand why ...
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Would the angle theta made during instantaneous speed is always same or not?

I hope you can understand that I am talking about instantaneous speed here.You can notice I have done summation of all small ds/dt in my photo. The angle which I have got it theta.I want to know is ...
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Why do we need instantaneous speed?

I am new to this topic and was just wondering about the use of instantaneous speed. I mean, we use to calculate the speed of car let us say at 5 sec. So we take the distance travelled in 4.9 to 5.0 ...
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Discretizing kinematics of moving object

I think this is a simple question, but I'm unable to find the relationship: The relative distance between two objects at any time $t$ can be written as: $x_r(t)=x_{ro}+\int_{t_0}^{t_f}v_r(t)dt$ where: ...
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6answers
357 views

Where did the kinetic energy formula come from? [duplicate]

I was looking for a proof for it and all rely on the work-energy theorem. But the work energy theorem relies on the kinetic energy equation. Ergo circular logic. So where did it come from?
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Calculating for total distance travelled vs position given $v(t)$ graph

It is currently to my understanding that the area under a $v(t)$ graph is the displacement of an object because $$\int v(t)dt = s(t).$$ However, some of the problems I have attempted recently give you ...
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Skipping stones on the surface of a non-static fluid — how to assess in vector space?

While skipping shells at the beach, I noticed the following: Waves approaching the shore impede the average velocity of my skip; retreating waves appear to do the opposite. This, of course, makes ...
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1answer
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Why is $(p’-p)^2 = -|\mathbf {p’} - \mathbf p|^2 + \mathcal O(\mathbf p^4)$?

On page 121 of Peskin and Schroeder, they claim that $$(p’-p)^2 = -|\mathbf {p’} - \mathbf p|^2 + \mathcal O(\mathbf p^4),$$ where $p = (m,\mathbf p)$ is the incoming 4-momentum of a particle in a ...
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2answers
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How to find position vector in Kepler orbit?

As the title says, I am trying to determine the position vector $r$, knowing true anomaly, semi-major axis, angular momentum and eccentricity vector. There is an equation describe the distance to the ...
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3answers
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Why doesn't an initial velocity affect the final velocity?

I've been stuck on a basic kinematics problem for some time, which usually goes something like this. Three balls are dropped from some height, $h$, with initial velocity $|v|$. Ball #$1$ is given $...
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2answers
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$\log\left(\frac{p\cdot p’}{(E^2-p^2)/2}\right)=\log\left(\frac{-(p’-p)^2}{m^2}\right)$?

On page 182 of Peskin & Schroeder, equation (6.17) ends with the equality: $$2\log\left(\frac{p\cdot p’}{(E^2-p^2)/2}\right)=2\log\left(\frac{-(p’-p)^2}{m^2}\right),\tag{6.17}$$ where $p=E(1,\...
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2answers
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Rotational kinematics of a non-rigid body. Equation of motion? [closed]

Two masses (of mass $m$) $1$ and $2$ are mounted on a massless rod. Mass $1$ is firmly bolted to the rod, mass $2$ can slide without friction along the rod. At $t=0$ the system is brought into ...

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