# 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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### Does a photon follow a straight trajectory in a thin transparent film? [on hold]

Emulsion films (developed by F.Powell) /by example/ show that elementary particles follow a straight trajectory staying in a film. The reason was clarified by Francis Mott in his famous 1929 paper ...
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### How do they know their velocity in a spaceship?

Suppose a spaceship is going to Mars or to Jupiter, they switch on their thrusters and accelerate for a certain period, how to they know their position / velocity, do they refer to the Sun?
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### Momentum of a rack and pinion gear system excited by a time variant force

Background I have a rack and pinion gear system as shown in the image below The pinion gear is attached to a flywheel at the back. The first state of the system, none of the gears or the ...
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### Projectile Motion

I know the angle at which a projectile is launched, how far it needs to go, and also the maximum height. How can I find the initial velocity needed (disregarding air resistance)? Currently, I am ...
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### Displacement of an object dropped from a cliff [on hold]

An object is dropped from a cliff. How far does the object fall in the third second? Assume that $g = 10 \, \mathrm{m/s^2}$. A: 10 m B: 20 m C: 25 m D: 45 m
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### How do I model the motion of a particle changing acceleration vector (2D)?

I want to model a particle with an arbitrary initial velocity, and estimate the time it takes to reach a final point given a constant magnitude of acceleration. It should take the quickest path to the ...
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### Rolling dynamics of round objects down an incline

If a cylinder is rolling down an inclined plane with inclination $\theta=30^\circ$ (with coefficient of static friction between cylinder and the plane $\mu_s=0.8$) without slipping and it has mass ...
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### The elevator and the bolt [on hold]

I had this question, I don't seem to get what I am doing wrong so here it goes:An elevator car whose floor to ceiling distance is equal to $2.7 m$ starts ascending with a constant acceleration of ...
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### Computing Acceleration in mass and pulley system using conservation of energy

I have a question in which a multiple pulley and mass system is being analysed. I can compute accelerations and Tension without any issue using newtons second law. However I am asked to use ...
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### Projectile motion maximum distance to origin

Is there an elegant or easy way to derive the maximum distance from the origin to a point of the parabola created by projectile motion (assume initial position is the origin)? Other than ...
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### Find the time (in seconds) Tom would need to catch Jerry [on hold]

I have a question about The 2015 ACM-ICPC Asia Phuket Regional Programming Contest Problem I.Tom and Jerry.The problem is as following. Tom and Jerry are very fond of cat and mice games, which might ...
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### Inverted pendulum with reaction wheel

I'm a little confused about the equations of motion of the reaction wheel pendulum. It is used in self balancing bicycles - see vide link in comments (I can't add another link here due to low rep). Or ...
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### Correct terminology for combined kinematic and dynamic state

The kinematic state is defined as the position and orientation in space. The dynamic state is defined as the associated velocities. What is the correct terminology for the combined kinematic and ...
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### non constant acceleration problem [closed]

The acceleration of an arrow from a bow falls from $6000m/s^2$ to zero when it leaves the bow after travelling a distance $x=0.75m$. Assuming that this acceleration can be expressed by the linear ...
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### Doubt on series springs

Here is a description of the motion of two springs in series. The premise is that the force on the two springs is the same. This is derived from the following reasoning: when I pull the mass with a ...
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### Water flow in salt solutions contemporary exposed to an electrical and constant magnetic field

When a permanent magnet is held motionless close to a salt solution which already has been exposed to an electrical field a flow in the water will be induced and can be detected by applying some ...
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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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### Projectile motion - calculate landing angle

A projectile is launched at a $45^\circ$ angle, aiming for a target at a distance of 15 feet away from, and $2$ feet below the starting position. I'm looking for equations to determine: The ...
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### Is the motion of a particle non-analytic?

I really can't understand what happens during the time $t(0)$ to $t(0+dt)$ in the following crackpot arguement: A particle is at rest (in an ideal frictionless world) until $t(0)$. So every order ...
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### Average Resistive force exerted by a wooden block on a bullet [closed]

A bullet of mass 0.04 kg moving with a speed of 90 m/s enters a wooden block and is stopped after a distance of 60cm. What is the average resistive force exerted by the block on the bullet? Ok, so ...
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### Stanford: “Objects in spacetime all move at constant speed $c$.” Are they right? [duplicate]

In this Stanford University lecture on Relativity, it is stated: Likewise, objects in spacetime all move at constant speed c in spacetime but if you change its direction, say by moving at speed v in ...
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### May a point rotate about itself?

Suppose we have two equivalent rigid cylinders. Cylinder 1 is moving (translating) with constant velocity of v. Cylinder 2 is rotating without slipping and its center’s velocity is constant and equal ...
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### Formula of distance traveled in Nth second by a uniformly accelerated body is dimensionally incorrect [duplicate]

$S_N = v_0 + \frac{1}{2}a(2N+1)$ This is the expression for the distance covered in the $N$th second of the journey, by a uniformly accelerated ($a$) body starting with initial velocity $v_0$. This ...
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### The dimensional formula of distance travelled in $n$th second

I read that the dimensional formula of distance traveled in $n^{th}$ second is same as that of velocity. Okay, the formula for the distance traveled in $n^{th}$ second is $s_t= u+\frac{a}{2}(2t-1)$ ...
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### How to calculate projectile path having starting and end point?

I want to show a projectile path between two points (x1,y1) (x2,y2 ) on graph. Here I know two points, start point and end point. I tried solving by taking launch angle as 45 degree, it doesn't seem ...
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### How does the relationship between velocity and net force affect the direction of a moving object?

I already know that for a moving object with velocity $\ v_i$,and has a net force, $\ F_{net}$, the trajectory of the object will start with the direction of $\ v_i$ and gradually deflect to the ...
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### Determining the forces required to maintain a static center of mass position; one with velocity and one with acceleration [closed]

I'm having a bit of trouble wrapping my head around this conceptually. The magnitudes and directions of the forces on two of the particles are indicated. What are the magnitude and direction of the ...
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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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### General motion of a cone on an inclined surface

Suppose that a solid cone is placed horizontally on an inclined surface and is initially at rest. How will the cone move when it starts motion due to its weight? I know that its motion depends on the ...
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### Where does movement come from? [closed]

When you put a body in motion, where does that movement come from? Ok, you will say things like "acceleration", but where does that acceleration come from? Then you might say "a force is creating the ...
In the brachistochrone problem and in the tautochrone problem it is easy to see that a cycloid is the curve that satisfies both problems. If we consider $x$ the horizontal axis and $y$ the vertical ...