# 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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### What is displacement time series?

For a car motion, I have time vector (starting from 0 to 40 with 0.1 increments) so that the time vector is something like $\begin{bmatrix}0&0.1&0.2&0.3&\ldots&40\end{bmatrix}$ and ...
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### Optimal “Blow up” Configuration

Suppose you have three balls glued together. Two are red and one is blue. The system of balls is blown up by an explosion of pure energy (that conserves the center of mass frame) exactly at the center,...
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### Maximum Momentum of Neutral Pion

I'm considering the reaction $p + p \rightarrow p + p + \pi^0$. To find the maximum momentum that the $\pi^0$ can have after this reaction in the center-of-mass frame, what I am doing is assuming the ...
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### Relativistic Kinematics - 2-Body Particle Decay

Consider the scenario where a particle of mass $M$ decays into two lighter particles of mass $m_1$ and $m_2$. In the center of mass frame (i.e. $\mathbf{p}_1$ and $\mathbf{p}_2$, the momenta of the ...
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### Throwing a basketball. What do I need to consider to hit a target? [closed]

This is a question that's been bugging me for some time now and the physics department at school is closed so yeah. Anywho, my question was, given a ball of mass .76, what forces would i have to ...
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### At what point does force stop translating an object and start purely rotating it? [duplicate]

At what point (or distance) from the axis of rotation, does force applied on a rigid body stop translating and purely rotating the body? Can such a point even exist? Does the body always have to ...
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### Average acceleration versus instantaneous acceleration

Does instantaneous acceleration also changes when direction of velocity changes. I know average acceleration does change.
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### How does Zeno of Elea's argument on “motion” make sense? [duplicate]

Zeno of Elea (born c. 500 bce) argued so intensely about motion. In one of his arguments he claims – in simple language – "that it is impossible to slap somebody, since the hand first has to travel ...
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### In circular motion, what's preventing me from calculating the circumference of the circle, dividing it by time to find the speed of the object?

There are equations to solve for the speed in circular motion. However, is there anything preventing me from calculating the circumference from the given radius, and then divide that over the time to ...
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### In an electron-positron annihilation, in what direction are the photons released?

I read that, in an electron-positron annihilation, at least 2 photons are produced, because of the law of conservation of momentum. my question is: in what direction are those photons released? and ...
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### Newtons 3rd law, on two opposing discs?

Assume we have a large disc at rest (bottom disc), which is free to move. Above it there is another disc (disc2) that's rotating, and a motor fixed on that large disc (bottom disc) as well, that load ...
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### How to solve Kinematics: two objects meeting in the air

A water balloon is dropped from the top of a 200m high tower. An alert archer at the base of the tower sees the balloon being dropped, waits for 5s, then shoots an arrow at 40m/s straight up towards ...
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### Can Theta be greater than 360 degrees in this equation?

I have a quick question regarding Rotational Motion. I understand the equation x = r (theta) and I know that theta represents the Angular Displacement for a circle but what if the linear distance ...
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### Confusing, can a motor on a moving disc stop the disc?

I've been troubled trying to solve this problem. If a motor is fixed on a moving rotating disc and the motor's rotor has another disc attached to it. What would happen if we attached the motor's ...
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### How does anything move? [duplicate]

So in order for two things $A$ and $B$ to move apart, for example, relative to each other, $B$ can be set into motion away from $A$. This means that we have to increase $B$'s velocity and therefore ...
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### Constrained Motion of Connected Particles, Small Calculation Question

I am looking at this sample problem from Meriam Kraige - Engineering Mechanics Dynamics: When I do the differentiation, I end up with $\large -2\dot y+\frac{x}{\sqrt{x^2+h^2}}$ Where is the $\dot x$...
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### Kinematics of a differential drive robot

(I am reposting here a question I asked on stack overflow, since it actually sits right in between programming (modeling of 2D physics) and physics proper (kinematics). I think I have the physics part ...
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### Why collide a moving particle with a particle at rest, rather than two moving particles?

I was just reading some lecture notes about relativistic and quantum mechanics, and in the later part of this page the author demonstrates that any relativistic particle collision in the "lab" ...
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### Is there a formula that gives the position of an object depending on the time, but which doesn't allow the object to surpass the speed of light?

I have found these two formulas: $v = at + v_0$ $x = \frac{1}{2}at^2 + v_0t + x_0$ a is the acceleration v is the velocity x is the position t is the time $v_0$ is the initial velocity $x_0$ is ...
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### Why is the range of a projectile proportional to the square of the initial velocity?

I was watching the MIT lecture about projectile motion and the lecturer asked why $$D=\frac{(v_0)^2\sin(2\alpha)}{g}$$ Why is it $(V_0)^2$ not $V_0$? It is a hypothetical question i know that the ...
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### Is this movement possible?

My friend and I were arguing over some random facebook shared video. On this video, one guy throws up a rotating stick then, while it rotates on air, he kicks through it. Is it even possible? Or is it ...
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### Projectile Motion [closed]

I've spent some time pondering the answer to this equation, without any success. A cannon is arranged to fire projectiles, with initial speed $v_0$, directly up the face of a hill of elevation angle ...
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### Find the average speed and velocity of the object [closed]

An object travels 11 m north and then turns around and travels 25 m south. If the total time of travel is 52 s what is the average speed and velocity of the object. I used the formula I was told ...
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### Do rotation matrices rotate about inertial or body angles? [closed]

I have Yaw, pitch, and roll angles in that order (Euler 321) to apply to a body reference frame in cartesian coordinate system. I want to know what the body reference frame vector coordinates are ...
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### A particle is constrained to move around the unit circle in the xy plane according to (x,y,z) = (cos(t^2),sin(t^2),0) t >= 0 [closed]

A particle is constrained to move around the unit circle in the xy plane according to (x,y,z) = (cos(t^2),sin(t^2),0) t >= 0 At what point should the particle be released to hit a target of (2,0,0)? ...
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### Insight into Torricelli's Equation ($v^2=u^2+2as$) [closed]

Torricelli's Equation ($v^2=u^2+2as$) is usually presented as the particular formulation of the SUVAT system which doesn't involve t. It is derived from the others using some (perhaps well-motivated) ...
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### Linear Momentum Based Problem [closed]

A ball moving along a straight line collides elastically with another stationary ball of the same mass. At the moment of collision the angle between the straight line passing through the centres of ...
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### Simple projectile motion question that I can't figure out [closed]

My initial choice was B, but apparently that should have been immediately eliminated. I simply found the root of the values squared. I know that horizontal motion would be constant velocity, and ...
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### Does circular motion cause centripetal force OR does centripetal force cause circular motion?

Does circular motion cause centripetal force, or does centripetal force cause circular motion, or are they both occurring hand in hand together instantaneously? One more question: If I project a body ...
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### Kinematics and dynamics - what pattern do they portray?

The Equations which are derived for kinematics and dynamics are some patterns related to the body in motion. What is the demarcation in the pattern that kinematic equations and dynamic equations ...
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### What is happening when a jenga block tower wobbles?

Imagine I am 3/4's of the way through a Jenga wooden block game. I have a tower and it is starting to wobble. To me it seems there are two possible causes for this: the wood is compressing and ...
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### kinematics: parabolic movement [closed]

How does the formula $ax^2$ is affected by the angle and the power of the launch of, let's say, a cannon ball, (regardless of its mass)? I am trying to create a simulation, and everything I have to ...
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### How does the object at constant speed pass the accelerating object?

A car starts from rest and move with constant acceleration of $4\frac{m}{s^2}$ and at the same time a motorcyclist moving with a constant speed of $36\frac{km}{hr}$ overtakes and passes the car. Find ...
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### Finding equation for exponential deceleration

Let's say my ship's velocity during deceleration phase is given by: $$v(t) = v_0 \exp(-k t)$$ where $v_0$ is the speed at the time of starting deceleration and $k$ is arbitrary constant. My ...
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### How to find stopping distance of a car? [closed]

I am trying to calculate minimum stopping distance of a car once the brakes are applied. I know the velocity at braking instant, i also know the distance from the obstacle. I found out that  d = \...
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### Time taken for a body to reach a velocity of sqrt(a) from 0 under an acceleration a? [closed]

Lets say body starts from rest and would like to attain a velocity of sqrt(a) , where a is the acceleration (constant) of the body. By laws of motion we get t = 1/sqrt(a) which in the case of a --> ...
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### Uniformly Accelerated Motion question

A ballast bag is dropped from a balloon that is 300 m above the ground and rising at 13 m/s. For the bag, find the maximum height reached. Now the book gives me this answer - $V_i$ = initial ...
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### My physics teacher gave us this equation $v= -3 +3t$

She asked us if the body was accelerating or slowing down, and I immediately said that it was accelerating (because the $a=3>0$). Then she said that I was wrong because the direction of the ...
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### vector and position and acceleration [closed]

I really need your help with two problems. Consider a moving object that can be described by the position function r(t) = [(8.00m/s )t-[( 4.50m/s^3 )t^3 ]î +(− 2.00 )t^2+10.0m]ĵ In unit­vector ...
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### Need help with acceleration question? [closed]

I don't understand how to solve this question involving two constant accelerations.
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### Kinetic energy on macro and micro situation

I just have this random question in my mind. If you drop something in deep space, and it falls due to a gravitational pull. As it's falling, its kinetic energy increases. I just wonder, is the average ...
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### How velocity progresses over time with a non-constant acceleration? [closed]

A $0.25\text{ kg}$ sphere of radius equal to $0.07\text{ meters}$ is dropped from rest from the top of a building. Granted that it will not hit the ground before, when and after what distance ...