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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3answers
50 views

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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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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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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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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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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2answers
58 views

Direction of acceleration in elliptical path

The $x$ and $y$ coordinates of a particle moving in a plane are given by x(t)=acos(pt) and y(t)=bsin(pt) where a, b(<a) and p are positive constants of appropriate dimensions and t is time. I know ...
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11 views

Trajectory of a charge in a electrostatic field which is generated by two charges

Consider the following case: We have a negative charge with position $$q = - 1, \quad \mathbf{r}(t=0) = \binom{9}{5}$$ which is placed into a electrostatic field. This Field is generated by two ...
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2answers
67 views

Why is the minimum work done not negative in this case?

I was going through my grade 10 physics textbook and noticed that $F S \cos 180^\circ$ (work done will be negative) is less than $F S \cos 90^\circ$ (work done is zero) but it is still stated that $F ...
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1answer
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Energy conservation in two-body decays?

Let's consider a generic two-body decay $A \rightarrow B + C$. In the center-of-mass frame (i.e, the rest frame of particle $A$), we know that the four-momentum of particle $A$ can be written as $p^{\...
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4answers
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What is the difference between m/s and m/s/s?

Can I subtract, say, for example, 600 m/s - 20 m/s/s? I am confused about this topic and there is no good information on the web.
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1answer
80 views

Is there a difference between instantaneous speed and the magnitude of instantaneous velocity?

Consider a particle that moves around the coordinate grid. After $t$ seconds, it has the position $$ S(t)=(\cos t, \sin t) \quad 0 \leq t \leq \pi/2 \, . $$ The particle traces a quarter arc of ...
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Time Dependent Spiral motion

I am trying to model a particle traveling through a high efficiency dynamic separator (which allows me to separate solid particles by their size) The problem boils down to spiral motion, in the radial ...
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1answer
66 views

How does $\langle 1/t\rangle$ denote a rate?

As a preface I should mention I am a mathematician and not a physicist, so I apologize if this question is elementary. I am going through an old paper of mathematical physics that I have been assigned ...
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2answers
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Harmonic motion: displacement

On my textbook the displacement in a simple harmonic motion is given as $$x = x(t)= A \cos(\omega t) \tag 1$$ It is true that $$x = x(t)= A \cos(\omega t)=A \sin(\pi/2-\omega t ) \tag 2$$ but why in ...
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Is velocity real?

This sounds like a stupid question but I am do not grasp physics concepts easily. "Velocity" is just the change in displacement over the change in time. I can see displacement and time as ...
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Need some help understanding velocity

I have just started learning kinematics and this is just a small question, that I wish for to clarified as it feels a little bit confusing. Below, the difference between speed and velocity is given. I ...
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1answer
142 views

What is the meaning of word 'rate' in physics?

Often, I have seen in physics the rate of change of velocity or something like that in kinematics. And in question based on speed, time and distance. I would like to know the meaning of the word rate ...
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1answer
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Two cars are moving away from each other. what is the frequency heard by observer in one of the car if the other blows a horn? [closed]

The cars are moving with same velocity in the opposite direction (one going south and the other is going north)
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Skier and ramp projectile [closed]

A skier leaves the ramp of a ski jump with a velocity of $v = 23.0\,m/s$ at $\theta =\,22.0°$ above the horizontal, as shown in the figure. The slope where she will land is inclined downward at $\...
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2answers
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Toss of a ball using a double integral

Let's say I want to calculate the height of a thrown ball: Let $x''(t)=-g$ and $x(0)=x(T)=0$ and $x'(0)=v_0$. One could then integrate 2 times and it is done. My professor told me to write it this way,...
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How can I convert coordinate accelerations to proper acceleration?

I need to calculate what an accelerometer would feel from the motions from a simulation. The simulation only gives position data in a global reference frame. How can I convert this global positioning ...
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2answers
41 views

Deflection angle of an alpha particle when colliding with a stationary nucleus

Is it possible to calculate the deflection angle of an alpha particle after colliding with a stationary nucleus with atomic number,Z,without actually knowing Z or for that matter without knowing the ...
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1answer
104 views

How to determine the minimum “Arrival Distance” given a maximum velocity, acceleration and jerk along with an initial velocity and acceleration?

Problem Given the following: $A$ - maximum acceleration. $J$ - constant jerk (the rate of change of acceleration). $v$ - initial velocity. $a$ - initial acceleration (where, in practice, $a ∈ [-A, A]$...
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What is a 'kinematic endpoint' in experimental particle physics?

In experimental particle physics, I see 'kinematic endpoint' pop up quite often. I've made an assumption of what it is but now I am not so sure. Example sentence: "This region is enhanced in B-&...
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If displacement is 0, does that mean initial velocity equals final velocity?

For instance, one of the kinematic equations is : $$v_f^2 = v_i^2 + 2ad$$ where $v_f$ is final velocity, $v_i$ is initial velocity, $a$ is acceleration, and $d$ is displacement. Say for instance a guy ...
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How to determine the distance travelled before a maximum acceleration is reached given a constant jerk?

Problem Given: An initial velocity and acceleration of 0. A maximum acceleration $A$ A constant jerk $J$ How might one determine the distance $D$ traversed before the maximum acceleration $A$ is ...
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1answer
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How to calculate the components of the displacement of unit magnitude of an accelerating particle in 2D? [closed]

A particle is moving in 2D having a constant acceleration $ \vec a $. Given initial velocity $ \vec u $, after time $ t $ the magnitude of its displacement $ \vec S $ is 1. I need to calculate $ S_x $...
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1answer
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$x$ and $y$ component in unit circle reversed?

Why is the $x$ component of the $r_2$ vector $\sin \theta$ and $y$ component $\cos \theta$ in the following example as one normally would expect them to be other way around? $$ \left. \begin{array} ...
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1answer
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Identifying variable in an ion thruster problem

recently came across a school revision problem introduced my teacher about ion thrusters. With the assumption that we are ionising air (Nitrogen) and that the ions accelerate by mutual repulsion ...
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357 views

Two formulas for relativistic energy - what is the difference?

To the best of my knowledge, relativistic energy $E$ of a body with rest mass $m$ moving at velocity $v$ can be expressed as either $$E=\gamma mc^2 \tag{1}$$ or $$E=\sqrt{m^2c^4+p^2c^2}\tag{2}$$ where ...
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Can I apply Newton's equations of motion to relative motion?

We know that Velocity of A relative to B is $$ \vec v_{A|B} = \vec v_A - \vec v_B $$ and Acceleration of A relative to B is $$ \vec a_{A|B} = \vec a_A - \vec a_B $$ So, is it correct to do this to ...
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48 views

If the velocity of an object is decreasing at a constant rate, does it mean that it's a uniformly accelerated motion?

If the velocity is constantly decreasing from $u$ to $v$ so is it uniformly accelerated motion?
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80 views

Confusion in coordinate transformation of acceleration vector

Consider this notation for vectors: $A_{cb}^{d}$ is the $A$ vector (velocity,acceleration, angular velocity or ...) of $b$ coordinate frame w.r.t. $c$ frame presented in $d$ frame axis. I know when we ...
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1answer
48 views

Projectile launched from an elevation onto a slope, why is the impact velocity in the Y-direction up (positive) rather than down (negative) [closed]

To solve for the impact velocity of the skier in the $y$-direction for part b) of the following problem, is it possible to use the formula: $$v_{fy}^2 = v_{iy}^2 + 2aΔd_y$$ Once I have solved for the ...
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107 views

Is this notation inconsistent? If not, can some explain why not?

Im working through a textbook section on particle kinematics. An example given is relating vertical velocity to horizontal velocity and states: $y$ has a constant velocity of $10 \ \rm [m/s]$ $y=(0....
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1answer
40 views

Static Analysis of a Diagram

It is very clear $M_A$ can not be zeros under general loading conditions, so this structure must be able to rotate about A. but the geometrical constraints will not allow it to undergo this rotatory ...
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1answer
47 views

Range of Iterated Projectile Motion [closed]

This is the question : Superman is throw inside one end of a room whose floor is made of kryptonite, his only weakness. He tries to fly using his mighty powers with an initial velocity $V_0$ at an ...
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Why distance equals initial velocity times time Plus acceleration over two times time Squared? [duplicate]

i am a beginner in physics and I do not understand why is the d=vi(t)+(1/2)a(t^2).
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2answers
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Problem in instantaneous acceleration and instantaneous velocity

Recently i came accross a problem that said An object is dropped straight down from helicopter the object falls faster and faster but its acceleration decreases over time becoz of air resistance. the ...
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Time taken to reach the ground, curved frictionless path vs. free fall

An object is released from rest in two conditions, one in which the object follows a straight path to the ground and one in which the object slides down a frictionless curved path. Will the time taken ...
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Query regarding instantaneous velocity and instantaneous acceleration

Suppose an object's velocity is $5 \ \text{m/s}$ at $t = 1$ seconds and $8 \ \text{m/sec}$ at $t = 2$ seconds then the acceleration here is $3 \ \text{m/sec$^2$}$ i.e at $t = 1$ seconds the ...
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Would it be easier to break a stack of planks joined together or when they have gaps between them?

If there is a stack of n identical planks (say n=5) and we need to break them (like in karate), would it be easier (i.e. would it require less force) if they are stacked together (figure on the left) ...
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3answers
76 views

What is the difference between two types of velocity?

What is the difference between $v=\frac{s}{\Delta t}$ and $\bar{v} =\frac{\Delta\bar{x}}{\Delta t}$, are they the same?
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4answers
370 views

Can we explain velocity without time? [closed]

I'm trying to wrap my head around inertia/velocity, or just change in general, I guess. I'm unsure exactly sure were my gap is, or what question to ask, so I'll explain with a scenario. Lets say I'm ...
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How exactly does motion produce thermal energy?

How exactly does motion produce heat? An electron that is moving from a higher energy state to a lower energy state can dissipate this energy as heat. Conversely, if the atom is provided with heat, ...
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1answer
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What is ground speed when falling vertically? [closed]

Ground speed as apposed to air speed. Assume a vacuum around the earth for simplicity. Just wondering if it's 0 or the absolute velocity versus the point of impact on the ground?
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2answers
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Can there exist a motion which cannot be described as a function of time?

I know there exist systems for which we cannot solve its differential equation, But I was wondering if there could be a motion that cannot be represented as a differential equation with respect to ...
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2answers
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Elasticity of spring and conservation of energy [closed]

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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3answers
41 views

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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2answers
59 views

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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