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
49 views

An ambiguous question on 2 balls [closed]

Two balls A & B are at rest at the bottom of a hill.Sometime after ball A is given a kick up the hill, ball B is also given a kick up the hill. When ball B is going up the hill, ball A is already ...
1
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2answers
60 views

Somewhat unusual projectile motion question

A stone must fly over two walls of height $h_1$ and $h_2$ $(h_2~ > ~h_1)$ from the side of the lower wall. The distance between the upper points of the two walls near which the stone's trajectory ...
-2
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2answers
42 views

How do I find the distance travelled in time $t$ in following question? [closed]

The particle starts from the origin with an initial velocity $u$ and the acceleration of the particle is increasing linearly with time $t$ as $bt$. Now what will the distance traveled by particle in ...
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2answers
32 views

When I kik a ball at velocity Vo, angle alpha, from the ground..(no air resistance) [closed]

I have the force acting on the ball equals to F = (Fx,Fy) = (0, -mg)? I mean I understand that I have the mg force on the y axis, pointing down, and I understand that there is no additional force on ...
1
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0answers
61 views

How could a heavy manhole cover jump out of the ground, fly through the windshield and hit a driver in a car?

Today (12 of Feb), there was this accident in Boston where a driver was killed because a manhole cover (~200lbs) had somehow become airborne and struck her. The car looks like an SUV, so her head must ...
1
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4answers
47 views

How can I calculate how high an arrow goes when all I know is its initial speed? [closed]

I'm not familiar with English physics terms so bear with me. If I shot an arrow straight up and it went off with a speed of 21 m/s, how high up would it go? (air resistance is insignificant). My ...
0
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0answers
36 views

Why does a curved spacetime result in a movement?

If gravity is not a force but a curvature of spacetime, where does the motion towards the center of gravity come from? To put it differently, why would two objects in a space fall towards each other ...
0
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1answer
29 views

If an object launches off of a table at a given velocity, calculate angle below the horizontal when it hits the ground?

So this is a basic kinematics question that I'm having trouble understanding. Here is the question verbatim: A hockey puck slides off the edge of a table with an initial velocity of 28.0 m/s and ...
0
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1answer
81 views

Calculating stopping distance of a car on a slope

I'm having trouble setting up a homework problem properly. We are given the following: A given car can brake to a stop from a speed of 60.0 mi/h in a distance of 123 ft on a level roadway. What ...
2
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1answer
36 views

A couple of questions regarding work to velocity exchange [closed]

I was tasked to express the velocity of the cube of mass $m$ at point B using the constants given in the picture below. Friction could be ignored, and the cube could be presumed to reach B with the ...
0
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1answer
33 views

a question on work and kinetic energy [closed]

A bullet has a mass of 0.02kg and is moving with a speed of 10m/s. It can penetrate 10cm of a given target before coming to rest. If the same target is only 6cm thick, what will be the speed and ...
1
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0answers
37 views

3 Particle problem with a difference

Please read this completely, it is not the typical question you expect. 3 particles are at the corners of an equilateral triangle with side a. Assume that particle 1 is at (0,0), particle 2 is at ...
0
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0answers
47 views

Finding the distance a spaceship would travel given a time of departure and velocity

Let's say a spaceship leaves Earth at a day t and with velocity v. Is there a way to know how many kilometers it will cover to arrive on Mars? This would be a trivial question were it not by the fact ...
1
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1answer
70 views

Difference between classic velocity and spatial velocity

I am reading a tutorial about a physics simulator I am using, and it has the following code (in C++, but not important): ...
-1
votes
1answer
96 views

Relative velocity of a boat traveling on a river [closed]

I am confused about relative velocity. So suppose a boat is traveling upstream on a river and a crate is dropped overboard. The boat continues to travel upstream for 60 minutes and reaches a ...
1
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1answer
34 views

How fast does a long object bent at the center need to be travelling in order to boomerang?

At an angle, of course. Standard pressure, average temperature, and calm wind. Bonus question: Can an object that is not bent boomerang at all? If yes, how different would the equations for this ...
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votes
1answer
40 views

a problem on circular motion [closed]

Question:A cyclist is riding with a speed of $7.5$ m/s. As he approaches a circular turn on the road of radius $80m$, he applies brakes and reduces his speed at the constant rate of $0.50$ m/s every ...
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votes
1answer
77 views

What's the formula for the speed of an accelerating car?

I am trying to find a formula that closely describes the speed of an accelerating car over time. I have found many graphs on the internet, but so far no formulae to generate them. For my purposes I ...
1
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1answer
68 views

Does this count as a proper derivation of the formula for work and kinetic energy? [closed]

$v_{av}$ = average velocity, $d$= distance, $a$ = acceleration, $m$ = mass Given: $$v_{av}*t=d$$ $$t=\frac{v_f-v_i}{a}$$ $$v_{av}=\frac{v_f+v_i}{2}$$ Then: $$\frac{v_f+v_i}{2}*\frac{v_f-v_i}{a}=d$$ ...
0
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2answers
47 views

How to interpret the equation of motion of a point that changes its acceleration

I'm trying to understand more deeply the equations of motion for a constantly accelerated 1D motion. Consider a point that moves with constant acceleration $a$ and that, at a certain moment $\tau$ ...
0
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1answer
49 views

Relationship $v_A^2-v_B^2=2a_t\Delta s $ for motion with constant tangential acceleration [closed]

I can not understand a relationship in the general motion in the plane. I am considering a point, which follows a curved trajectory. Indicate A and B two different position of the trajectory and $v_A$ ...
1
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4answers
67 views

Introductory physics: first second of free fall

While doing my physics homework I encountered an acceleration problem that I've been unable to solve. Here, is the data table of the objects motion. At 1 second, why does the "Dist-meters" slot of the ...
-1
votes
1answer
56 views

Finding angle between two displacements [closed]

Consider two displacements, one of magnitude 6 m and another of magnitude 8 m. What angle between the directions of this two displacements give a resultant displacement of magnitude (a) 14 m, (b) 2 m, ...
0
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0answers
17 views

Calculating the distance of a piston from the crank center

I stumbled upon this [https://en.wikipedia.org/wiki/Piston_motion_equations#/media/File:Piston_motion_geometry.png ] and was wondering, if you can determine the position of the piston (x) by the law ...
1
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0answers
35 views

How to find tangential and normal unit vector to a trajectory from the equation?

Considering a 2D motion in a plane and the equation of the trajectory of a point $y=f(x)$, I don't understand how exactly $\frac{\mathrm{d}y}{\mathrm{d}x}$ can be used. In particular if I'm looking ...
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2answers
56 views

accelerating and non accelerating duality of matter

Kinetic energy of any object , assumes accelerating nature of the object as it is derived from equations of motion for uniformly accelerated objects and the work-energy theorem which deals with ...
1
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0answers
46 views

What happens if an aeroplane travels in a pilot mode in a straight line with no stop? [closed]

Ex. If a plane flew upwards straight it would reach outer space but what happens if it travels below the horizon in a straight line. Will it be traveling around the earth? How? And what about it if it ...
0
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0answers
14 views

Relations between unit vectors in polar and curvilinear coordinates

I'm a bit confused about the relations between unit vectors in curvilinear and polar coordinates in a plane. Let $u_{R}$ be the radial unit vector in polar coordinates and $u_{N}$ the normal unit ...
1
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0answers
22 views

Calculation max speed for a particular speed profile, distance and time?

For work I have to calculate the maximum speed for a machine. The machine has a certain speed profile which must be followed. Besides this this speedprofile has to be followed within a certain time ...
1
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0answers
28 views

Is there a way to find the optimal angle to launch an object to get maximum distance when there is an initial height? (Projectile motion) [duplicate]

I know that the optimal angle to launch an object at ground level is 45 degrees; however, i want to know that if there is anyway to get the optimal angle to launch an object to get the maximum ...
0
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2answers
34 views

(+)/(-) Acceleration & (+)(-) Velocity

Does a negative acceleration mean an object is slowing down? Does a negative velocity basically mean you are moving at an opposite direction? The sign is just direction?
0
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0answers
13 views

Height estimate by step profile?

With so many current apps in mobiles tracking number of steps based on analyzing the accelerometer's measurements in time during a walk, I was wondering the following: Would it be possible to ...
1
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2answers
91 views

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 ...
4
votes
1answer
28 views

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 ...
0
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1answer
83 views

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 ...
1
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1answer
36 views

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 ...
0
votes
1answer
59 views

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 ...
0
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2answers
70 views

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 ...
0
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0answers
30 views

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 ...
1
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1answer
63 views

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 ...
-1
votes
1answer
28 views

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 ...
23
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2answers
1k views

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 ...
1
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1answer
39 views

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 $A$ ...
4
votes
2answers
169 views

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 ...
1
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1answer
55 views

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 ...
1
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0answers
43 views

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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0answers
69 views

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 ...
0
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1answer
36 views

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 ...
0
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1answer
34 views

Methods to use in problems with equations of motion, where is required to determine a particular acceleration

I've a doubt on problems with manipulation of equations of motion. I'll make an example of a situation I'm confused about. Let $A$ and $B$ be two points that move on a line with constant speed, ...
-1
votes
1answer
116 views

Position from velocity time graph [closed]

I have taken Calculus before but unfortunately no equation is given so I have to do it the old way. An object is at x = 0 at t = 0 and moves along the x axis according to the velocity-time graph ...