# Tagged Questions

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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### Can we say that the instantaneous velocity of an object is the displacement in zero time?

Can we say that the instantaneous velocity of an object is the displacement in zero time? In the image above the instantaneous velocity of the object as change in time gets closer and closer to ...
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### Shouldn't motion be represented as a Taylor series rather than a finite sum of functions or a polynomial? [closed]

Since the change in velocity of an object at rest prior to time $t_{0}$ implies a change in acceleration — that is, let's postulate, $\mathbb{P}$, the object would have remained still, so there was ...
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### Rate of deceleration for an average speed [closed]

I'm trying to figure out how to answer this problem: A car is driving at 11 m/s, when it begins to brake. Over the next 25 meters, it averages 6 m/s. At what rate does the car decelerate? Assume a ...
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### What happens to kinetic energy of an object when i stop its motion? [duplicate]

Assume an object is moving and it is stopped at a point . Now kinetic energy will transform into some other energy . what can be those energies and on which cases these will happen respectively ? ...
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### Photon energies after neutral pion decay

I am trying to find the photon energies of the decay $\pi_0 \rightarrow \gamma\gamma$ and their dependence on the pion energy $E_{\pi}$, its initial velocity $\beta$ and the scattering angle between ...
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### Time Given Distance and Velocity Vectors [closed]

I recently came across a problem that gives velocity and two positions (which I solved for distance) in vector notations (). My question is, given the vectors for velocity and distance, how do I solve ...
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### For a bob on a pendulum following simple harmonic motion, what causes the bob to accelerate towards the centre of equilibrium?

*The position of equilibrium being the position of the bob when the string is taut and vertically downwards. When I draw a simple diagram, I see that the tension of the string, which always acts ...
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### What are the major differences in group-skydiving as opposed to “single” skydiving?

Surface area/the cross-sectional area is greatly increased, so my thinking is it should decrease terminal velocity as well as a couple of other factors. But mass changes too (since there would be more ...
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### Kinematics equations of motion find x position in 2D from height

I have a question and I thought of 2 possible ways to answer it however the resulting answers are different which means I must be doing something wrong in my calculations. All the below happens 2 ...
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### Searching for acceleration to minimalize path or time

I am thinking about motion of one point starting from $(0,0)$ and with velocity $\mathbf{v}(0)$. What is the acceleration $\mathbf{a}(t)$ with condition $|\mathbf{a}(t)|<M$ that minimalize ...
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### Work done: kinetic energy or area under F-ds curve?

Starting from $$F=ma = m \frac{dv}{dt} = m \frac{ds}{dt} \frac{dv}{ds} = m v \frac{dv}{ds},$$ leads to work done = integral of F.ds = integral of mvdv = change in KE. Suppose a variable force is ...
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### Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newton's third law and momentum conservation. Here is what I have tried. Lets take a ball mass of $m_1$ (index 1 is the ...
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### Can velocity be an undefined quantity?

We have the image below displaying the uniform velocity by time-distance graph. At every point velocity is constant but what if distance and time both become zero as at origin in the graph is? The ...
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### Prove the relation between relative velocity ,momentum and energy

In Chapter 8 of F.Mandl's book Quantum field theory, during the derivation of the differential cross section, the following relation is used: $$E_1E_2v_{rel}=\sqrt{(p_1p_2)^2-m_1^2m_2^2} \,\, ,$$ ...
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### Kinetic Theory of Gases: Why do gas molecules have translational motion?

The title pretty much asks the question. I was reminded of the Kinetic Theory of Gases recently and I am puzzled as to why gas molecules would have any translational motion. Is it because collisions ...
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### cross over to another object that has same height with our last position, is that really possible?

I have got confused with this. Well..In that picture, lets say the height is 8m, and the car moves and going to cross over to another object that has the same height with its last position..my ...
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### Describing the motion of a point-mass [closed]

Consider a point-mass moving around a fixed point on a circle with radius $r$ with constant angular velocity $\omega$. At a certain moment of time, the connection is removed, and the point-mass flies ...
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### Different results for displacement using different Kinematics equations

We drop an object from a height. It displaces a distance $L$ in the $\vec{y}$ direction. So: $$L = \frac{1}{2}at^2$$ Or: $$v^2-v_0^2 = 2aL \rightarrow L = \frac{v^2}{2a}$$ How much would the ...
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### How to calculate the horizon line of a satellite?

I need an equation to calculate a list of Earth-centered, Earth-fixed (ECEF) XYZ coordinates on the earth that represent the visibility limit of satellite given its ECEF XYZ coordinates. For any ...
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### Is velocity always tangential to trajectory?

So I was doing an exercise and they find find the angle between the tangential of trajectory and the vertical I was stuck but then I read in a site that the velocity is ALWAYS tangential to the ...
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### Inclined plane, circular motion and the friction

Suppose we have a cylinder on an inclined plane of mass $m$ and radius $R$ moving without sliding (so that $\varepsilon = a/R$). Why is the friction $F$ causing the circular motion sometimes lower ...
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### Adding rotations onto a vector

I have a vector with spherical co-ordinates $(r_1,\theta_1,\phi_1)$, then I want this vector to be rotated by $\theta_2$ $\phi_2$ spherical angles but I cannot figure out how. I have tried using the ...
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### Find time-parametrization given path and speed of a particle [closed]

Consider a particle in two dimensions with position vector $r(t)=<x(t),y(t)>$ and the shape of the path is described by a function $y(t)=f(x(t))$ (Thus $r(t)$ is a parametrization of $f$ with ...
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### About using screw in air compression and air Engine [closed]

I want to use screw to build compressed air engine, as following image As I designed, this screw rotate in a tube My Question is: How successful this idea? Note: If this question not related to ...
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### Kinematics problem regarding motion of a particle [closed]

A particle of mass m moves on the $x$-axis as follows: it starts from rest at $t = 0$ from the point $x = 0$, and comes to rest at $t = 1$ at the point $x = 1$. No other information is available about ...
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### How does momentum effect velocity? [duplicate]

I'm in AP physics and we haven't even covered this yet so sorry if my question seems strange... I know $p = m v$, However right now I am writing a 2D physics engine and I am having some trouble with ...
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### How do you measure the acceleration of two objects with different masses? [closed]

I would like to know how to measure the acceleration of two objects with different masses...(and the formula that's used.) For instance a steel ball that, say...weighs 67g and a wooden ball that ...
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### Relating momentum fraction to rapidity in a high-energy collision

It's a well-known result in particle physics that in an underlying interaction like this: assuming $p_0^-,p_{0\perp},m_0\ll p_0^+$, $m_1$ and $m_2$ are small, but $p_{1\perp}$ and $p_{2\perp}$ are ...
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### Computing the Initial Velocity of an orbiting body

I'm working on a simulation program that replicates the movement of planets around a large celestial body (the sun). This is a three dimensional simulation that uses vectors. At present, I'm ...
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### How to account for inertia in kinematics?

Alright, I'm only in AP Physics and I asked my teacher and he couldn't help me... I'm making a 2D physics engine and I'm having problems when it comes to gravity between objects and I think its ...
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### What is the point of this type of graph? (Projectile) [closed]

What is the point of graphing vs range, during kinematic motion?
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### Problem in deducing the equations of motion using indefinite integral

As we know, antiderivative or indefinite integral is the function the derivative of which gives the actual function. Let $F(x)$ be the derivative of $f(x)$ ie. the instantaneous rate of change of ...
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### What is the movement of the material point? [closed]

The parametric formulas for movement of a material point are: $x(t) = A \sin (kt)$ $y(t) = B(1 - \sin(kt))$ Describe the movement of the MP. That is the entire question and I can't find a ...
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### Change velocity formula from a function of displacement to a function of time [closed]

I have this problem from my dynamics book and I can't figure out how to solve it. I've played around with all the formulas and asked a few friends who did the course in the previous years but I can't ...
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### Velocity of car down an Inclined Plane

I was learning to make a car game and came across this situation where my car is on an inclined plane. It's initial velocity is 0. Now, the problem is that my memory serves me this formula to ...
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### Finding acceleration and distance when velocity given

I am trying to do the following question for practice (it is an interview question), and I don't know if my methods and answer are correct. Given a velocity $v=2+3t^2$, find acceleration after 3 ...
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### Minimum power to pull a sheet of paper [closed]

I'm trying to tackle a question in kinematics, but I miss something and don't know what. The question goes like this: Let a homogeneous pole of mass m be connected to ceiling and lean on the ...
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### Does rotation increase mass?

If an object is rotated on its axis near the speed of light would its mass increase? Normally if the object was moving (in relationship to the Earth for example) I would agree that its mass would ...
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### Finding the Angle of Launch for a Cannon Projectile to Hit a Specific Point [closed]

A cannon with barrel length of $l$ was placed with its base at the origin $(0,0)$. A ball was fired with the initial speed of $v$ as it leaves the barrel at an angle of $\theta$ above the horizon. ...