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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Maximum range of a projectile on an inclined plane with explain [closed]

I have tried everything searched the internet but unable to find a proper solution to this question
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1answer
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Finding the mass of an egg from impulse necessary to break it (from dropping it) [closed]

I came across this simulation from https://www.physicsclassroom.com. It didn't say how much force was necessary to break the average egg, so I looked it up (link): It takes 25 Newtons to break an ...
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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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260 views

2-D motion Question [closed]

A bottle dropped from a balloon reaches the ground in 20 s. Determine the height of the balloon if (a) it was at rest in the air and (b) it was rising with a speed of 50 m/s when the bottle was ...
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1answer
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Tracking the path of two point masses through time under the influence of gravity and with no initial velocities [duplicate]

Given the point mass $p_1$ at $(0,0)$ with mass $m_1$ and the point mass at $p_2$ at $(r,0)$ with mass $m_2$ how would you find the positions of $p_1$ or $p_2$ at any time. My first thought was to ...
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1answer
262 views

kinematics question involving velocity and time [closed]

A particle starts moving rectilinearly at time ${t = 0}$ such that its velocity '${v}$' changes with time '${t}$' according to the equation ${v = at^{2} - bt}$ where ${t }$ is in seconds and ${v}$ in $...
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1answer
80 views

Motion in a plane [closed]

I have a question which says that a particle moves in the $xy$ plane according to the relation $x = Asin(qt )$ and $y= A - Acos(qt) $, where A and q are constants. I have to figure out the distance ...
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6answers
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Distance from a velocity time graph where acceleration is not constant [closed]

In the following question I calculated the distance with methords actually only applying to constant acceleration. I thought this applicable because the question was asking for an approximation. I ...
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1answer
168 views

Deriving an expression for the tangential velocity of a meteor orbiting the Earth? I have 2 expressions, not sure which is correct [closed]

"A meteoroid of mass $m$ is on a circular Earth orbit of radius $R$ which is a few (> 2) times larger than the radius of the Earth $R_E$. Derive an expression for the meteoroid's speed. State the ...
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1answer
105 views

Constant acceleration of an object [closed]

Why when an object keeps moving at a constant acceleration, it's speed is not always greater than 0?
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1answer
299 views

How would you go about solving this tricky distance problem? [closed]

I've tried calculating the distance the runner has left to get to the finish line by the time the bird gets there and adding it to the distance the bird has to fly back to the runner. Then I ...
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1answer
939 views

How do you know when to use kinematic equations as apposed to $v = d/t$ and $a = v/t$? [closed]

How do I know when to use v = d/t and a = v/t or d=vi+​1/2​​at^2 and vf = vi + at?​
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2answers
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3 Stones Problem (High School Physics) [closed]

I couldn't figure out how to do this question: 3 stones of different mass (m, 2m, 3m) are thrown vertically upward with 3 different velocities (v, 2v, and 3v, respectively). Rank from high to low ...
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1answer
76 views

Simple Kinematics question [closed]

So this is a pretty simple kinematics question I was working on but I completely skipped over a derivation. Here's what I did to solve for the first part: I'm wondering if there is anyway to solve ...
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5answers
118 views

Can the initial time be non-zero?

I am just slightly confused about how initial time is chosen in mechanics. I keep thinking I have understood it but some doubts come up later. Basically when I derived the constant acceleration ...
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1answer
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Finding Difference in Time with no displacement [closed]

I have a very simple kinematics problem on my hands for my homework, I cannot ask anyone right now, and it is basically a test grade so I want to get it right AND understand it well. Two boats ...
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1answer
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How to express in terms of spacetime intervals the average speed of one participant having moved between two suitable others

Given a flat region of spacetime as set $\mathcal S$ of events together with values of spacetime intervals (up to a common non-zero constant) for each pair of events, $s^2 : \mathcal S \times \mathcal ...
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3answers
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What does $t_0$ mean in constant acceleration equations? [duplicate]

I am using the book Understanding Physics by Mansfield and O'Sullivan. In their derivation of constant acceleration equations, they initially use a time $t_0$ that is not necessarily $0$. They get $v=...
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4answers
620 views

What is the evidence for the existence of gravity [closed]

I have recently been wondering that what good evidence proves the existence of gravity (besides the Cavendish experiment). I would like straightforward answers that are on point. I will be willing to ...
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2answers
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What does the $2g$ mean? $v_y^2=v_{0y}^2+2g(y-y_0)$

In the relationship $$v_y^2=v_{0y}^2+2g(y-y_0),$$ what does the $2g$ mean? Why do we have gravity being multiplied by 2? Don't say you need to know calculus; I know that. I don't want to know how ...
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2answers
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Speed in min/km given distance in meters and time in seconds

How to calculate speed in min/km given distance in meters and time seconds? I used formula v = d/tbut having problems converting units. I've tried ...
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3answers
489 views

How many equations are there to calculate distance?

I am an app developer and I am trying to build a physics app to calculate distance based on the quantities the user gives. for example if the user gives initial speed, time and acceleration, using ...
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2answers
176 views

Kinematics problem invloving position and time [closed]

An object is moving along X axis with position as a function of time given by $x = x(t)$. Point $O$ is at $x = 0$. The object is definitely moving towards $O$ when 1. $\mathrm dx/\mathrm dt < 0$ ...
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3answers
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Velocity and acceleration with displacement [closed]

Find the velocity and the acceleration for a moving object with displacement $= te^{-t}$. The $e$ is the exponential function.
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1answer
115 views

Doubt in understanding what is really meant by a vector [closed]

Sorry for asking a very common question. For now this is a question which make me depressed for about an year. As a mathematics student I studied vectors very axiomatically which makes me feel ...
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2answers
142 views

Use equations to create a realistic problem [closed]

Given the following equations: $100$ m = $0$ m + ($50 \cos\theta$ m/s)$t_1$ $0$ m = $0$ m + ($50 \sin\theta$ m/s)$t_1$ - $\frac{1}{2}(9.80$ m/s2$) t_1^2$ I am supposed to make up/create a real-life ...
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2answers
431 views

Is it possible to calculate distance if non-constant acceleration is unknown? [closed]

I know that the distance travelled in non constant acceleration is $d=\int_a^b f(x)\mathrm{d}x$, but is it possible to calculate the distance without knowing the value of $f(x)$?
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1answer
60 views

Why does $a=v/t$ not work for light? [closed]

if acceleration = velocity/time and light takes approx. 8 minutes to reach from the sun to earth doesn't that mean light is accelerating at 37,500,000 m/s^2 ?
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1answer
397 views

What is acceleration of acceleration? [duplicate]

What is it called when object A is accelerating at rate B, but rate B is also accelerating at rate C. What is it called? How does it work? How can I apply it?
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1answer
433 views

Is there a tool online that lets me convert acceleration-time graphs into velocity-time and position-time graphs?

Basically I need to visualize a few physics exercises and I need a tool that let me to convert the acceleration graphs into the other types So that, I can get an idea of the relation of acceleration ...
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2answers
203 views

How many years would it take the Pioneer space probe to travel to Proxima Centauri with its current speed? [closed]

Pioneer space probe moving at a speed of $30km/s$. Assuming its heading for Proxima Centauri, which is situated at $4.2ly$ from earth, calculate how long it would take to get there in years, to the ...
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3answers
3k views

Speed of an object in air versus in vacuum

Okay, imagine that you are shooting a rocket down a tunnel that is 60 miles long and the rocket is travelling at 60mph, so the rocket should reach the end of the tunnel in a hour, right? Yep, in an ...
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1answer
44 views

When to use what centripetal acceleration? [closed]

There are two equations for it: $a_c = v^2 / r$ and $a_c = \omega^2 / r$. It seems like they give me different values. I don't know when to use which. Can you explain?
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1answer
67 views

Newton's 2nd law of motion and mass-energy equation [closed]

According to the mass-energy equation $E=mc^2$, so $m=\frac{E}{c^2}$, but according to Newton 2nd law of motion $F=ma$, so $m=\frac{F}{a}$. Therefore $\frac{E}{c^2}=\frac{F}{a}$, or $E=\frac{Fc^2}{a}$....
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1answer
244 views

Projectile motion question : time at which velocity v becomes perpendicular to initial velocity u? [closed]

A projectile is thrown up with the initial speed u, making an angle theta (theta > 45 deg) with the horizontal. What is the time, just after which, it will be moving perpendicular to its initial ...
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1answer
111 views

What kinematic formula is this? [closed]

I think it's one of the kinematic equations but I don't recognize the form. $$d = d_0 + \frac 1 2 a_{cc}t^2$$ It was given in a physics problem,where we are given points (x) and (y). where $x = t^2$...
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2answers
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How to solve this problem? [closed]

A ball is projected vertically upward with a speed of $ 50 $ m/s , I need to find out the speed at half the maximum height. What i have done, Found the maximum height by $ H = \frac{u^2}{2g} $ and ...
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3answers
5k views

Are constant acceleration and zero acceleration same? If they are different, in what context? [closed]

If initial velocity is 5 m/sec and acceleration is zero, then the body moves with a constant velocity 5 m/sec. The graph is a horizontal straight line(v=u+at). However, my question is how a body moves ...
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1answer
126 views

How can a fly fly in a car? [duplicate]

From my understanding. if the car is moving at the velocity of 10 m/s and the fly is moving at the velocity of 5 m/s. the fly must move backward at the velocity of 5 m/s. but the fly seem to be able ...
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3answers
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Kinematics Issue

I have tried my best to understand why I get different answers for the following questions. Why does the equation matter? Question 1: A groundhog running at $2.00\space ms^{-1}$ passed a dog ...
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1answer
2k views

Max height and time [closed]

Wes stands on the roof of a building, leans over the edge, and drops a rock. Lindsay waits 1.20 s after Wes releases his rock and throws her own rock straight down at 21.0 m/s. Both rocks hit the ...
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1answer
99 views

An ambiguous question on 2 balls [closed]

Two balls A & B are at rest at the bottom of a hill.Sometime after ball A is given a kick up the hill, ball B is also given a kick up the hill. When ball B is going up the hill, ball A is already ...
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2answers
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If x is the position, how and why is one sure that a is displacement and b is acceleration in the given equation? x=a+bt²

I don't understand why a and b have to be displacement and acceleration respectively. Is that because of kinematics fist equation v-u+at?
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1answer
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Particle with non zero acceleration with zero velocity at that instant - example [duplicate]

Is it even possible for a particle to have those properties?
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1answer
457 views

What is the relation between position vector, relative velocity and time? [closed]

Two particles having position vector r1=(3i+4j)m and r2=(-5i-3j)m are moving with velocity v1=(4i+3j)m/s and v2=(ai+7j)m/s collide after 2 seconds then the value of a is (i solved it graphically but ...
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1answer
749 views

Difference between kinetic energy and force [duplicate]

I hope I don't make myself look stupid asking this question. Please note I'm relatively new to physics but am extremely interested. To test myself, I made up a time, velocity, and mass and filled in ...
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1answer
1k views

What is meant by negative direction of velocity? [duplicate]

What is negative velocity and negative direction of the velocity?
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2answers
660 views

Why the bob leaves the circular path when tension in the string becomes zero [duplicate]

In vertical circular motion of a bob attached with a string, we say that the bob leaves the circular path when tension in the string becomes zero. But even when tension becomes zero there's always a ...
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1answer
33 views

How to find acceleration in this rectilinear movement? [closed]

$$x = A + Bt + Ct^2 + Dt^3 $$ where $$C = 0.14~\rm m/s^{2} $$ and $$D = 0.01~\rm m/s^{3} $$ After how much time after the start of movement does the acceleration become 1 m/s^2 and what is the ...
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1answer
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Trajectory in a plane field [closed]

Can someone please help me understand this problem with trajectory. It isn't explained very well in book. $x(t)=a\cos\omega t $ $y(t)=\frac{b}{\omega^2}(1-\cos\omega t)$ $a,b,\omega >0 $ and are ...