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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1answer
46 views

Free fall into circular motion

If I'm on a roller coaster free falling from height h and then suddenly start going into horizontal motion with a radius r of turn what is the g-force I experience? I worked out the equation like ...
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0answers
19 views

2 balls projected upwards, find the place of collision [on hold]

Problem: A ball is thrown upward with velocity $19.6ms^{-1}.$ A second later, another ball is thrown upward with velocity $9.8ms^{-1}.$ When and where will these 2 stones collide? I recently ...
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0answers
20 views

Question of mechanics? [on hold]

There are two parallel train . One of the train overtake another one in 20 second and that train crosses another train in 10 sec. The length of train is 200m How to calculate the velocity ? Here is ...
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0answers
25 views

Speed at time of impact [on hold]

A car runs off the road and hits a stationery rock. Some glass pieces from the windscreen are projected forward and were found at an average distance of 15 meters from the car. The average height ...
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0answers
17 views

At time t=o a body is thrown vertically upward with a velocity u at time t=t [on hold]

At time t=o a body is thrown vertically upward with a velocity u at time t=t another body is thrown with same velocity u . when that two body will meet together ?
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7answers
8k views

I need help with finding distance traveled

How do I find the distance traveled of an object if the speed is not constant?
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1answer
35 views

Change of direction in physics when an object in motion stops

Consider an object moving with an acceleration $a = -1 \text{m/s}^2$ starting with speed $v(0) = 4 \text{m/s}$ towards east and stopped after 4 seconds. (There are no friction.) After 4 seconds, the ...
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1answer
166 views

Finding the total energy in centre of mass frame

I'm working through a problem in a special relativity textbook (Woodhouse) and I'm having some difficulty. I have to show that if I have a particle of rest mass $M$, total energy $E$ colliding with a ...
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2answers
104 views

Projectile, air resistance and wind

So for my school project I am working on a projectile simulator and air resistance. So I have looked at this. Equations for an object moving linearly but with air resistance taken into account? ...
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1answer
28 views

How to know if a body is travelling with uniform acceleration or not?

One of the Example in my Textbook is A body travels a distance of 2 m in 2 seconds and 2.2 m in next 4 seconds. What will be the velocity of the body at the end of 7th second from the start. In ...
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4answers
57 views

Can we observe two different events occuring at the same point?

I was wondering a situation. Suppose a train is moving with a certain acceleration. It turns on its front light at a certain time, and it's back light say t s after. But to a inertial, or non ...
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1answer
97 views

Which point in the graph does a parachute open?

The diagram represents speed-time for a sky diver. He falls freely from an aircraft then opens a parachute and later lands safely on the ground. At which point did the parachute fully open? ...
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1answer
108 views

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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0answers
25 views

Would momentum be conserved in teleportation? [closed]

Defining teleporation loosely as at least quantum tunneling all of your particles and preserving the arrangement. If that doesn't work, assume the mechanisms of the most basic definition of ...
0
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1answer
60 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 ...
0
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1answer
76 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
676 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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0answers
31 views

Hitting a skateboard while riding it [closed]

I am rigidly sitting on a skateboard, the skateboard and I have a total mass of 100kg. I have a hammer that weighs 50 kg. If i swing the hammer and hit the skateboard parallel to the ground with a ...
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0answers
25 views

Free fall motion of a body [closed]

A ball is projected vertically upwards with an initial velocity of 100m/s. Find the speed of the ball at its maximum height Take g=10metre per second square.
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0answers
21 views

Motion of particle in $T$ seconds [closed]

A particle starts moving from rest position ($v = 0$) under a constant acceleration $a$. If it travels a distance $\Delta{x}$ in time $T$, what distance will it travel in the next time $T$?
2
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5answers
4k 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 ...
0
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3answers
39 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
23 views

Vectors and projectile [closed]

Two particles A and B starts moving from a high point O at t=0 in the opposite direction with horizontal velocities 9 3 m/s and 4 m/s respectively. Due to earth's gravitational field the two particles ...
0
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1answer
35 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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0answers
24 views

Angle to move in to cross river w/ a current? [closed]

so I have a hw problem given that a swimmer is swimming 1.2 m/s relative to the river and they swim across trying to get the a point directly opposite the 74 m wide river but they end up 33 m ...
3
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2answers
272 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
40 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
165 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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0answers
32 views

Does “$\mathbf r[~t~]$” correctly denote the trajectory of a point particle wrt. a reference system w/o having to decide on a particular origin? [on hold]

Consider a specific geometric reference system, e.g. a specific inertial frame(1): the suitable set of point particles $\mathcal S := \{ H, J, K, ..., O, P, Q, ... \}$; and consider one other point ...
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4answers
131 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 ...
0
votes
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 ...
1
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1answer
299 views

Tangential and radial acceleration in projectile motion

I'm currently learing kinematics, specifically projectile motion and as an example in my textbook is a bullet fired at some angle. I understand the derivation of formulas to describe that motion and ...
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3answers
495 views

Determine resultant velocity of an elastic particle-particle collision in 3d space

So I have two particles that have collided in 3 dimensional space. I want the particles to rebound off of each other in an elastic manner. How do I determine the resultant velocity vector if I know: ...
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0answers
37 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 ...
1
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1answer
151 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
19 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
62 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 ...
7
votes
1answer
293 views

Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
0
votes
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 ...
-2
votes
1answer
75 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 ...
0
votes
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 ...
-4
votes
1answer
46 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
498 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 ...
0
votes
2answers
180 views

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 Newtons third law and Momentum conservation. Here is what I have tried. Lets take $m_1$ (the ball) hits $m_2$ (the man). ...
1
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2answers
215 views

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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2answers
33 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 ...
0
votes
1answer
62 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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votes
2answers
31 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 : ...
0
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3answers
626 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 ...