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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62 views

Are perpendicular components special in vectors?

We can split a vector (velocity/displacement vector) along any two directions as long as the resultant of the oblique components of the vector is same as my original vector. Similarly if we have to ...
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1answer
80 views

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 ...
8
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3answers
791 views

Radius of curvature

I have come across a question that asked me to find the radius of curvature of a projectile. As far as I know, the path of a projectile is a parabola and I have found mention of the radius of ...
2
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1answer
32 views

Is motion along the $x$ and $y$ axises independent with quadratic drag?

It's often stated that motion in the $x$ and $y$ axises are independent, so that changing the $x$-velocity will not influence changes in the $y$-velocity. To me it seems that with quadratic drag (drag ...
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5answers
5k views

Force applied to wheel in pure rolling motion at contact point with road [closed]

Suppose a wheel with radius $R$ is resting on a non-inclined surface. A torque $\tau$ is applied to the wheel center. In an attempt to prevent wheel from spinning, the ground applies a static friction ...
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40 views

Displacement based on acceleration in km/h$^2$

For calculation of displacement based on acceleration and time, I have the formula below: $$ x = v_0t + \tfrac{1}{2}at^2 .$$ If I get $a$ in km/h$^2$, and $x$ in km and $v_0$ in km/h and I suppose ...
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1answer
41 views

Calculating time and speed change on downhill incline

I am trying to calculate the time and final speed if lets say a bike with constant speed of 20km/h of goes in this incline (downhill), what would be its speed after say $M$ meter ? I remember the ...
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2answers
276 views

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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3answers
42 views

Acceleration derivative

I am reading Morris Kline's "Calculus" and I fail to understand this notation: We have acceleration to which an object $r$ feet from the center of the earth (and above the earth) is subject. If we ...
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5answers
166 views

Why do two formulas $d = v_0 t + \frac{at^2}{2}$ and $d=vt$ yield different results?

All of you are sure to be familiar with these two equation: $d = v_0 t + \frac{at^2}{2}$ and $d=\overline vt$ Given the same initial and final velocities, and time and acceleration. With the ...
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4answers
142 views

Is magnitude of velocity same as speed?

Is magnitude of instantaneous velocity same as instantaneous speed? More specifically, is $$\left|\frac{d\vec{r}}{dt}\right| = \frac{d|\vec{r}|}{dt}\; .$$ Also Is it wrong to say that ...
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1answer
2k views

How to find speed from Newton's law?

I have a question about Newton's law. The question says block A(mass 2.25kg) rests on a tabletop. It is connected by a horizontal cord passing over a light, friction less pulley to hanging block ...
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0answers
46 views

Dynamics and kinematics of quantum field theory

What is the difference between dynamics and kinematics of quantum field theory? I read that in QFT there is no possibility to keep the two things distinct because of a problem with the separability of ...
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1answer
183 views

Zero velocity and non-zero average acceleration

Can you have a zero velocity and nonzero average acceleration? I am confused with the word "average" here. If the question would be, "Can you have a zero velocity and nonzero acceleration?" my answer ...
2
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0answers
20 views

Motion decomposition (Relativistic case)

When an electron moves at very close at $c$ (speed of light), is it physical to decompose the motion in two other directions (like what we do in classical case). If so, the motion in each direction ...
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2answers
64 views

Question about kinetic energy

I have a question about kinetic energy: Imagine two vehicles with velocities $v_1$ going at $30 \frac{\text{m}}{\text{s}}$ and $v_2$ at $50\frac{\text{m}}{\text{s}}$. If they hit each other, will ...
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1answer
41 views

Derivation of $V_f^2=V_i^2+2a\left(x_f-x_0\right)$

I'm reading this book on Classical mechanics, and they show a derivation of the mentioned kinematic formula: $V_f^2=V_i^2+2a\left(x_f-x_0\right)$ They start by saying that the acceleration of an ...
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1answer
83 views

Why Aristotle made mistake about motions law? [closed]

Hi I was studying Aristotle motions law and comparing them with Newton. He states that heavier body fall faster than slow ones. I really can't understand how he could committed such a mistake...I mean ...
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0answers
14 views

Determining the range of values for separation angle (Landau problem)

I encountered a problem while reading the following exercise from the second Landau & Lifshitz volume: Determine the range value in the $L$-system for the angle between the two decay particles ...
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1answer
49 views

Proof of (Vi + Vf)/2

Its quite intuitive that when you have constant acceleration, the average velocity is given by (Vi + Vf)/2, but how can you prove it?
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3answers
505 views

How does this chair move?

I have a chair like this(shown in figure). I was kneeling on the part where we sit. I just gave a sudden push to the part where we rest the back, without moving my legs. I found that the chair is ...
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2answers
37 views

Find the force needed to accelerate body to a certain velocity for a certain time with respect to drag force

So, the problem is straightworward when we suggest that air resistance force is constant: $$ \vec F = \frac {\vec V_1 - \vec V_0} {t} m / b $$ $$ \vec V_0, \vec V_1 - \text {initial and final ...
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1answer
63 views

Woman arrives 6s late for the train. Find her velocity to reach it [closed]

A woman arrives exactly 6 seconds after a train leave the station at a constant acceleration of $0.4m/s^2$. Find the minimum constant velocity she might run to get in the train. What I did: I wrote ...
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2answers
32 views

Problem with velocity vector [closed]

Question: The radius vector of a point depends on time $t$, as $\vec{r} = \vec{c}t+\dfrac{\vec{b}t^2}{2}$ where $c$ and $b$ are constant vectors. Find the magnitude of velocity. My attempt : ...
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3answers
630 views

I am unable to combine two equations in kinematics [closed]

Sorry people, very basic kinematic stuff here. (1) Velocity: $$v=\frac{d}{t}$$ (2) Acceleraton: $$a=\frac{v_{f}-v_{i}}{t}$$ (3) Re-arrange acceleration: $$v_{f} = v_{i}+at$$ (4) Ok here is my ...
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3answers
4k views

Proof of centripetal acceleration formula ($a_c = v^2/r$) for non-uniform circular motion

The formula for centripetal (radial) acceleration is well known, and there exist many proofs for it: $$||a_c|| = \frac{||v||^2}{r}$$ However, all the proofs I've seen rely on the fact that it is ...
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3answers
156 views

How do we calculate instantaneous velocity in 2D?

Suppose a body is moving with a constant speed of $10~\mathrm{ms^{-1}}$ in negative $x$ direction in $x$-$y$ plane. Let $\vec r$ be the position vector. Then what will be the instantaneous velocity ...
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2answers
30 views

Kinetic energy dissipation in braking a vehicle

Let's say a vehicle that weighs 20t is hauling along at 50m/s and we want to brake it down to a full stop. The kinetic energy we need to dissipate into heating up the brakes is ...
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2answers
340 views

Acceleration: A ball sliding down the inside of a semicircular bowl

Edit: To clarify, this is a homework question. But I couldn't care less about getting the answer to this specific question as it's not even assigned yet. It looks interesting and I want to understand ...
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1answer
29 views

Muting a bell with a resonating object

I recently moved into an apartment next to a church with bells and since then I haven't stopped dreaming of ways to mute them. I've been thinking about a design but I'm a little unsure of the ...
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2answers
49 views

When considering the acceleration as constant? [closed]

I'm solving a simple dynamic exercise, exercise says: "What is the absolute value of the force necessary to speed up a 500kg mass subject to 1600km/h in 1,8s, with the object from rest?" Then I had ...
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2answers
54 views

Why does the sound of my tea stirring go up in tone the faster I stir?

I've noticed that when stirring my tea, as I stir faster the tone generated by the stirring goes up. Why is that? Is it something to do with the Doppler Effect? EDIT -------------------------- ...
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1answer
77 views

Is it right? time < 0?

I'm doing the solutions of Halliday's book kinematic exercise, given the equation of acceleration:$$a(t) = -30t.$$ One wonders when the acceleration is positive. In a resolution, says that for t < ...
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1answer
59 views

A problem on rectilinear motion in a car [closed]

Today, I attempted the third question in the first chapter (Physical Fundamentals of Mechanics) in the book Problems in General Physics by I. E. Irodov. The question goes like this: A car starts ...
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1answer
54 views

How do I set when the object isn't moving

I started studying instantaneous velocity derivatives using only now. It may seem stupid but really I'm not sure whether that's right: I have an equation: $$x (t) = 1.5t - 9,75t³$$ To set the time ...
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1answer
31 views

If velocity for an interval is zero then is acceleration also zero throughout?

We know that if velocity is zero for an instant, then acceleration need not be zero (a simple example of which is a ball thrown upwards.) But if velocity is zero for an interval, will ...
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0answers
41 views

How to locate the initial speed? [closed]

I have this question: Two men were delivering a crate of mass $100~\text{kg}$ to a house up a hill which is inclined at $35^\circ$, when it dropped and slid down the hill. The coefficient of ...
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0answers
27 views

Bezier curve and deceleration

I have a question regarding calculation of a bezier curve. I'm programming an app where in there's continuous straight line motion of a vehicle at a constant speed. (Let's call it 'u'). When the user ...
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3answers
191 views

Uniform Circular Motion and Centripetal Acceleration

In introductory physics books (or at least mine) it limits the equation $a_c=v^2/r$ to the situation where the speed around the circular path is constant. It enforces the idea that the speed is ...
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0answers
23 views

Why are springs shaped as they are? [duplicate]

It must have something to do with Hooke's Law and their tendency to have a restorative force as equal to the distorting force as possible; but I'm not sure. Help please?
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0answers
19 views

Differences between empiric laws of Galileo and Kepler

Although in both cases we encounter empiric laws, as far as I know Galileo's laws of motion differ in some way from Kepler's laws of planetary movements. In what way?
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2answers
47 views

What is a good book to learn AP Physics C? [duplicate]

I am looking to learn AP Physics C (if you are not acquainted with the curriculum see here), both the mechanics part and the electricity/magnetism part. I have not had much exposure to an AP-style ...
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3answers
69 views

Angular acceleration - radial & tangential

Since ever I knew that radial (angular acceleration) is equal to $ W^2 * R = V^2 / R $ and that the tangential depends in the situation (School physics & calculus). Recently I encountered the ...
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2answers
7k views

Preventing a block from sliding on a frictionless inclined plane

I want to demonstrate what force $F$ you would have to exert on an inclined plane of angle $t$, mass $M$ to prevent a block on top of it with mass $m$ from sliding up or down the ramp. I worked out ...
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1answer
39 views

Minimum distance between two bodies attached by a spring

Take two bodies of masses m and M attached by a spring of constant K on a smooth horizontal surface. The system is at rest. A constant force F acts on body M, horizontally. To study the motion of the ...
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0answers
38 views

Total cross section of particle decay

Suppose a particle A travelling along the $z$-axis and decays into particles B and C. The cross section is given by $$\frac{d\sigma}{d\cos\theta^*} = k(1+\cos\theta^*)^2$$ where $k$ is a constant ...
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1answer
100 views

Trajectory of a swimmer trying to reach the opposite bank [closed]

I came across the following question 2 days ago: $Q$. A swimmer is swimming in a river with a speed $u$ with respect to the speed of water which is $v$. It is assumed that the river has straight ...
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0answers
36 views

Projectile motion with wind

I am trying to simulate a projectile motion with wind and gravity. (I'm a programmer so excuse my knowledge on the subject) I want to know launch rotation of a person in 3d to throw a ball forward ...
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1answer
105 views

How fast would one have to travel in an airplane in order to experience a continuous sunset?

For the sake of simplifying this problem and removing any guess work on how high the plane is flying, we'll say that our airplane is at 30,000 ft. as this is the average altitude for commercial ...
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1answer
33 views

Kinetic Energy - use a log scale or not? [closed]

Lets say we have a series of balls and an eggs. All items have equal mass but are traveling at different velocities. Thus they have differing kinetic energies. Now, for each 'ball' object we have, ...