# 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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### Motion of an object in a moving car and collison

I came across an interesting question today at work. 'Imagine traveling in a car. The passenger has a glass bottle in their hand. In which direction relative to the moving car should the passenger ...
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### Transformations and kinetic energy

From the equation $E_k=\frac12mv^2$ you can determine more energy is necessary to accelerate a mass the higher your initial velocity is. For example, three times more energy is necessary to accelerate ...
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### Two Trains Relative Motion

I am confused about finding the solution to this relative motion problem: You are on a train traveling east at speed of 20 m/s with respect to the ground. Your friend is sitting on another train ...
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### equation for velocity vs displacement for nonlinear acceleration [closed]

An object starts out at t=0, s=0 and accelerates with A=sin(pi*t/T), where T is defined as (pi/2 * Vmax/Amax). Vmax is maximum velocity, and Amax is maximum acceleration. Solution is restricted to t=...
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### Conservation of momentum always? [closed]

Consider two atoms A and B, with A at rest and B in motion towards A. As soon as B is in the atomic field of A, will it stop with its energy going into B or will it just move up to a postion where ...
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### Calculating time using SUVAT equations with unknown initial velocity

I understand that the equation used to find the equation used to find displacement when the initial velocity is unknown is: $vt-(at^2)/2$ how would you rearrange this to solve for $t\;?$ When I try ...
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### How can one prove mathematically using a thought experiment that a simple pendulum will vibrate forever in an ideal condition (no friction) [duplicate]

Let's say I have a simple vibrating pendulum, if there is no friction in the space, will it vibrate forever or will it stop? How can one prove this mathematically? I tried but failed, can somebody ...
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### How to sensor Jerk=$d^3{\bf r}/dt^3$, or higher derivatives (4th, 5th, 6th order) when applied in the equation of motion of a ballistic missile?

Given a 6th order differential equation of motion as usually used in ballastic missile dynamic models. What kind of sensors are usually used to measure Jerk, (or higher order derivatives in kinematics)...
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### Relative velocity

Question is from Barron's SAT subject test Physics "A flat railroad car is moving to the right at 5m/s. A person standing on the car throws a ball straight upward at 20m/s. If air resistance is ...
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### Why do most office chairs have 5 wheels?

(Inspired by Why are four legged chairs so common?) I've been wondering for a while... Why do most wheeled office chairs have 5 wheels? My guess would be that while stability vs. simplicity ...
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### Conditions which guarantee that two points do not collide?

Consider two material points $A$ and $B$, with $B$ following $A$, moving with linear motion at constant speed and with $v_A<v_B$ (which means that, excluding possible decelerations, $B$ and $A$ ...
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### How do the postulates of relativity relate Lorentz transforms to their inverses?

This question is about one of the assumptions involved when one is deriving the Lorentz transformation, for example under "Principle of Relativity" in Wikipedia's page on the derivations. Let me ...
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### Given a current velocity and a fixed input energy, how much faster will a relativistic particle be?

The relativistic kinetic energy of a particle with mass $m$ and velocity $v_0$ is $$m c^2 (\gamma_0 - 1) \textrm{ where } \gamma_0 = \frac{1}{\sqrt{1 - \frac{v_0^2}{c^2}}}$$ I would like to know how ...
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### Needed acceleration input to reach a target point

I have a point mass traveling on a 2D plane with some initial velocity v and initial position r. The point mass is able to ...
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### Two trains collision problem [closed]

Consider two trains $A$ and $B$ travelling on a line one towards the other at speed $v_A=v_B=90km/h=25m/s$. When they are $511m$ apart the driver $A$ start braking with deceleration $a_A=1.25m/s^2$...
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### Tunnel through center of the earth, how to find period using $adx=vdv$?

Suppose the boulder enters a tunnel dug through the center of the Earth along a diameter starting at rest. How would one calculate the time it takes for the boulder to reach the other end of the ...
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### Which Method for finding velocity of an object in the mirror is correct? [closed]

My Professor asked a question, "A person is seen jogging in a rear view mirror of focal length $1$m. He is at a distance $39$m from the mirror. His jogging speed is given to be $5 \frac{m}{s}$. ...
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### Point rolling on a ball [duplicate]

Assume we are provided with a perfectly spherical and frictionless ball of radius R. A point is placed on the top of the ball. A velocity u is imparted on the ball to one side of the ball. How can we ...
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### How does Initial velocity effect braking distance? [closed]

supposed we have a car that slams the brake to bring it to stop, how would doubling it's mass affect braking distance and how would halving its velocity affect it? I used the equation d=Vi^2/2×a
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### Will the speed of the wind produced by a fan increase continously to infinity with the propeller spin speed?

Imagine a scenario: On a stand, an $RC$ plane motor is mounted on a stand. The motor has a $8x4$ prop attached to it. In the theoretical model, if the spin of the motor can be increased infinitely ...
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### 2D - What is the next point given a start point, velocity, yaw rate, acceleration, and time change?

In a two-dimensional environment: Given: a starting point (x1,y1) an initial velocity (speed and 2D heading/direction) a constant rate of turning (yaw, since there is no roll or pitch in only two ...
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### In perfect vacuum (no external force), if I apply a small amount of force to a body, will it continue to accelerate forever?

According to the equation $F = ma$, the greater the force applied to a body, the greater its acceleration. But in a place where there is no gravity or any other kind of external force, if I apply a ...
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### Why the distance equation is not working while calculating distance manually?

I was wondering how the average velocity is the arithmetic mean of initial velocity and final velocity if acceleration is constant. So, my first part of the question: Can someone give me an algebraic ...
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### Why does a stream of water behave like this when aimed against a spoon or into a glass?

I noticed while doing everything except the dishes that water behaves quite strange. These two things might be two different phenomenon, but the water acts in a similar way in both cases. Spoon and ...
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### Period of mass in circular motion [closed]

I've been trying for 4 days now to solve my physics lab assignment but now I'm starting to think there must be a mistake in the question. You know those rotating mass experiments where you have a mass ...
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### Automobile Air bags [closed]

This is a problem that has many answers on google but I don't understand what is the underlying logic of the steps taken. Here's the problem The human body can survive an acceleration trauma ...
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### Is the Earth's molten outer core affecting its motion?

According with the seismological studies [1] the outer core, with thickness of about $2300km$, starting from depth of $2,900 km$ and ending at $5,200 km$ is a low viscosity fluid, consisted mostly of ...
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### Correct formulas for two wheeled robot motion

I'm trying to write a simulation of a two wheeled robot, which can be controlled by varying the speeds of his wheels, independently. However, the physics engine that I'm using can only rotate a body ...
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### Relativity collision problem [closed]

Here is the problem: A body of mass m (I assumed this is rest mass, but not 100%), and momentum p(subscript m) collides with a stationary particle of mass M. Find the available energy in the CM frame....
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### What numbers do we examine when predicting how much damage an object will do when it strikes another object?

A 1,000 pound boulder at rest is pushed with a constant acceleration for 6 seconds, causing it to move 30 feet. It then strikes a medieval castle wall made of stone and mortar. If we know nothing more ...
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### Kinematics question. A falling object falls [closed]

This is quite bad for me as I'm a third year physics student now, however I'm attempting to go back on my old first year work as a refresher, but I'm completely stuck on a question! Can anyone help? ...
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### Confusion regarding resolution of forces

I'm looking at a basic free body diagram of a car travelling on a banked(inclined) road with inclination theta. It's mass is 'm'. Here the diagram shows weight (mg), Normal reaction(N), and ...
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### Acceleration in Space

Lets assume a body with a certain mass is in a region of space that has zero $g$ (or pretty close to zero $g$). Would acceleration in a straight line produce $g$-forces? Would that mass acquire ...
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### Unit Vector Displacement [closed]

A particle starts from the origin at $t = 0$ with a velocity of $+4.0\mathbf{j} \text{ m/s}$ and moves in the $xy$ plane with a constant acceleration of $(6.0\mathbf{i} + 4.0\mathbf{j}) \text{ m/s}$....
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### Is the Coriolis acceleration formula just an approximation?

The Coriolis acceleration given in textbooks is: $a_{cor} = -2\omega v$ When trying to understand the derivation, it seems as though this is just an approximation. And to illustrate this I give a ...
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### Can I call the component of tangential acceleration towards center of circle as the centripetal acceleration?

In my textbook the definition for centripetal acceleration is given, "The acceleration produced by virtue of change in velocity direction is centripetal acceleration" This definition is irritating. ...
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### At a fixed inital velocity, What throwing angle will give the projectile the most trajectory length? [closed]

This is a diagram of a projectile motion: Given a constant initial velocity, What angle gives the most trajectory length? By length I mean the length of the parabola from the point the ball is shot ...
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### Is there mechanical strain on a wire along the direction of current flow?

The (attractive) magnetic force on two parallel wires can be seen by the two wires bending towards each other. This can be explained by the Lorentz force acting on the charges and the charges "pulling"...