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.
5
votes
5answers
1k views
Why does work equal force times distance?
My 'government-issued' book literally says:
Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
2
votes
2answers
622 views
What is displacement? Position relative to a reference point or change of position
What is the "official" or most useful definition of displacement in the context of kinematics?
There are two common ones:
Displacement is the length and direction of a line from a fixed reference ...
0
votes
1answer
137 views
Looking for a way to simplify a physics formula [closed]
I have the following physics formula:
$$d = \frac{1}{2} at^2$$
where d is equal to half (at) squared
where:
d is distance
a is acceleration
t is time
I need to simplify this to get the ...
0
votes
2answers
194 views
Find vector position in time give this graph?
Graph is position x position. There are 3 points, $A$, $B$ and $C$.
$A(0,2)$
$B(4,2)$
$C(6,0)$
Particle travels from $A$ to $B$ and from $B$ to $C$ at constant $v = 2 ~m/s$.
Find vector ...
3
votes
1answer
1k views
How do kinetic energy and linear momentum relate?
It took me quite a long time to click my gears in place and even then I'm not sure it's completely correct.
The problem is that I need to understand these concepts (physics concepts; not just these ...
0
votes
1answer
77 views
A Satellite's Perspective
If a planet is spinning east to west and there is a satellite spinning from west to east...
Can the satellite travel at a speed sufficient to make the planet appear, from the vantage point of the ...
3
votes
1answer
142 views
A practical deceleration question
My friend is a U.S. Army paratrooper. Today, through an unfortunate series of events, he was jerked out of a C-17 traveling at 160 knots by his reserve parachute. First-hand accounts describe it as he ...
-1
votes
1answer
1k views
Question on Projectile Motion equation [closed]
A golf ball is shot into the air from the ground. If the initial
horizontal velocity is 20m/s and the initial vertical velocity is
30m/s, what is the horizontal distance the ball will travel ...
1
vote
2answers
123 views
Trains travelling at different speeds towards a station C
Here's the question:
Consider two stations A and B located 100 kilometer apart. There is a station C, located between A and B. Now trains from station A and B start moving towards station C at ...
2
votes
2answers
199 views
What is the displacement of an accelerated and relativistic object?
Displacement in an accelerated classical object is:
$$s=ut+\frac {at^2}{2}$$
What is the displacement of an accelerated relativistic object?
In Newtonian mechanics there are two types of ...
3
votes
3answers
1k views
Maximum range of a projectile launched from elevation “dumbed down”
I am trying to conceptually understand why the angle which produces the greatest range for a projectile launched with an elevation is not 45 degrees. I have exausted all other options, and I hope that ...
1
vote
1answer
1k views
Simple Projectile Motion Question
A volcano erupts 50m below the sea level. A rock leaves the crater at 20 m/s at an angle 30 deg with the vertical line. The rock has a mass of 15kg. IGNORE WATER RESISTANCE. It gets out of the water, ...
3
votes
2answers
313 views
Can these figures demonstrating the safety of “Archery Tag” arrows be correct?
There is a new sport called "Archery Tag" that involves shooting opponents with foam-tipped arrows fired out of a real bow. The official Archery Tag web site presents data that claims to show the ...
1
vote
1answer
645 views
What's wrong with this equation for harmonic oscillation?
The question:
A particle moving along the x axis in simple harmonic motion starts
from its equilibrium position, the origin, at t = 0 and moves to the
right. The amplitude of its motion is ...
0
votes
2answers
279 views
Does acceleration at an angle to velocity change the direction?
During an interval of time, a tennis ball is moved so that the angle between the velocity and the acceleration of the ball is kept at a constant 120ยบ. Which statement is true about the tennis ball ...
1
vote
2answers
216 views
Kinematics Problem
The question asks me to find the angular velocity.
Now I do not want you to solve my homework, I want explanation please.
It states that the acceleration of point P is $\vec{a}= -3.02 \vec{i} ...
1
vote
2answers
386 views
Sign of Velocity for a Falling Object
I'm working on a homework problem in Mathematica. We have to graph the height and the velocity of a function given an initial height and initial velocity. However, when I do the graph for the velocity ...
0
votes
1answer
650 views
How do I know an initial speed of a thrown object using the max height [closed]
The simulation being referred to is in box2d
An object is thrown to the max height of $h$ with gravity of $g$, what is it initial speed?
I tried the following:
$v = v_0 - g t$
$0 = v_0 - g t$
$t ...
0
votes
1answer
223 views
Calculating the launch angle of a horizontal launch (mechanics) [closed]
I need some help with the following question:
A smooth spherical object (the first object) is projected horizontally from a point of vertical height H = 26.38 metres above horizontal ground with a ...
0
votes
1answer
470 views
Projectile motion question: vertical and horizontal graph
I've have got some vertical and horizontal distances for a projectile-like motion.
In order to work out the trajectory, why is it better to plot on the x-axis, "horizontal distance^2", and on the y ...
7
votes
2answers
834 views
Should acceleration be included in state vector of a Kalman filter?
I'm developing (actually adopting existing solution) a Kalman filter to model motion of a vehicle (UAV or automobile). The state vector will include position, velocity, and, possibly, acceleration.
...
0
votes
3answers
245 views
Deccelerate and Accelerate to achieve timed journey
I have a vehicle traveling at initial speed $100\:\mathrm{m/s}$.
Expected destination speed is also $100\:\mathrm{m/s}$.
Maximum deceleration is $3$.
Maximum acceleration is $10$.
Distance to the ...
0
votes
2answers
505 views
What will be the relative speed of the fly? [duplicate]
It has happened many times and i have ignored it everytime.
Yesterday it happened again .
I was travelling in a train and saw a fly (insect) flying near my seat.
Train was running at a speed of ...
1
vote
1answer
617 views
How to find acceleration given position and velocity?
Sorry for this very simple question but I am still very new to the laws of motion.
I am dealing with 2-dimensional vectors in my programming environment and I'm following these slides to learn about ...
0
votes
1answer
344 views
Question of force of friction on incline plane [closed]
An object of mass $4\text{ kg}$ starts at rest from the top of a rough inclined plane of height $10\text{ m}$. If the speed of the object at the bottom of the inclined plane is $10\text{ m/s}$, and ...
0
votes
1answer
105 views
Simplifying some math for an ant-on-rubber-band problem
OK, I've been doing this problem for fun (it's a great problem, BTW!): http://www.physics.harvard.edu/academics/undergrad/probweek/prob76.pdf
Here is the solution: ...
0
votes
1answer
955 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
votes
1answer
392 views
The acceleration of a particle moving only on a horizontal plane is given by a= 3ti +4tj, [closed]
The acceleration of a particle moving only on a horizontal plane is given by a= 3ti +4tj, where a is in meters per second-squared and t is in seconds.
At t = 0s, the position vector r= (20.0 m)i + ...
2
votes
1answer
137 views
What is the origin of the naming convention for position functions?
In physics, position as a function of time is generally called d(t) or s(t). Using "d" is pretty intuitive, however I haven't ...
1
vote
2answers
548 views
Calculating Impact Velocity Given Displacement and Acceleration
Assume a car has hit a wall in a right angled collision and the front bumper has been displaced 9 cm. The resulting impact is 25g. Also, it is evident by skid marks that the car braked for 5m with ...
1
vote
2answers
75 views
Acceleration: Value Disparity?
If we consider a ball moving at an acceleration of $5ms^{-2}$, over a time of 4 seconds, the distance covered by the ball in the first second is $5m$. In the 2nd second will $5 + 5 = 10m$. In the ...
0
votes
2answers
350 views
How to compute drag coefficient given initial position, initial velocity and final resting position?
The equations I'm using are:
x = x + (DT * vx)
vx = vx * C
My DT is always 0.01 and the coefficient C (related to a linear ...
0
votes
0answers
63 views
Relativity Scenario [closed]
Does anyone have any ideas about this scenario? I'm having trouble comparing what happens at the different speeds. It has to do with simultaneity
Suppose Al is at rest standing in between two sets ...
0
votes
2answers
185 views
Question Concerning Position Of A Particle At Any Given Time
After years of procrastinating i've decided not to "move ahead" with physics without getting this ridiculously trivial question clear!*I know i had asked a similar question as silly and stupid as this ...
2
votes
2answers
331 views
How to calculate a firing location from point of impact data?
I would like to know how to calculate the point at which a bullet is fired from a gun given information from the scene where the bullet falls. The scene would contain the point of impact (GPS ...
7
votes
5answers
549 views
Should you run when under rain?
When it's raining, would you get less wet if you run or more wet?
I think you will get less wet, because rain is coming down in a constant volume and if you run you will have a shorter amount of time ...
1
vote
2answers
219 views
Using acceleration to plot position
Sorry if this question is dumb, and I know is physics 101, but I'm not that good with physics.
I'm writing an iPhone program that by collecting the acceleration data of the device tries to replicate ...
0
votes
2answers
852 views
What do I need to do to find the stopping time of a decelerating car? [closed]
The question is:
A car can be stopped from initial velocity 84 km/h to rest in 55 meters. Assuming constant acceleration, find the stopping time.
Sorry for my ignorance, but I need to review ...
0
votes
2answers
186 views
Why wouldn't this system of equations determine where two balls meet?
A ball is thrown vertically upwards at $5\text{ m/s}$ from a roof top of $100\text{ m}$. The ball B is thrown down from the same point $2\text{ s}$ later at $20\text{ m/s}$. Where and when will ...
1
vote
1answer
293 views
What's the difference between arc length and signed distance?
Suppose I give you a position function $x(t)$ where t is time and x is position. Then i ask you to find the total distance travelled from $t = 0$ to $t = t_f$.
Which formula would give you that ...
0
votes
1answer
124 views
I think I disprove this with kinematics, but energy says it is right
!
Here is my kinematics argument. For now I am only going to look at ball 2 and ball 3. Make note of the following data.
$|v_0| = 10m/s$, $y_0 = 10m$, $\theta_2^0 = 30^0$, $\theta_3^0 = -45^0, g = ...
5
votes
2answers
248 views
what is the kinematics of a particle with complex mass?
particles with real-mass have time-like kinematics ($ds^2 > 0$).
particles with zero-mass have light-like kinematics ($ds^2 = 0$).
particles with imaginary-mass have space-like kinematics ($ds^2 < ...
2
votes
1answer
116 views
If 2 bodies are moving at equal speed parallel, and one throws something at a right angle to itself, will the thing thrown hit the other body?
Me and some friends were discussing the idea of (in a perfect scenario, no air resistance or gravity to affect the results) 2 bodies moving in the same direction exactly parallel to each other.
If ...
1
vote
2answers
391 views
2d simulation shooting projectiles that inherit the gun's veocity at a moving target while also moving
Overview: I'm working on programming a simulation that requires 'shooting' projectile-type objects at other moving objects. How can I calculate the angle at which to shoot the object to hit?
Details:
...
0
votes
0answers
73 views
What is the acceleration in this case? [closed]
An object travels from point "A" to "B" towords East with velocity of 10 m/s . And then it travels form point "B" to "C" towords North (CHANGE IN DIRECTION) again with velocity of 10m/s . So in this ...
2
votes
8answers
1k views
Real world examples for projectile thrown upwards or downwards
I am preparing a physics course for high school about projectile motions. If a projectile moves with initial velocity $v_0$ in the gravitational field of the earth, the equation
$$
s(t) = 1/2 g t^2 ...
0
votes
2answers
315 views
How to calculate total distance and time a puck will move?
To simulate a puck's movement, I use the following model (please restrain from discussing the model, it makes the simulation look the way I want it to) and would like to know how to calculate the ...
7
votes
4answers
417 views
Why does a ping pong ball change direction when I spin it on a table?
When I spin a ping pong ball on the table, it rolls forward in the opposite direction of the spin, and then eventually changes direction and rolls backward.
Here's a video demonstrating the effect.
...
0
votes
2answers
424 views
Basic Free Fall Problem [closed]
So I am trying to remember my childhood doing some Physics problems, but seems that I forgot almost everything. But it's not a big thing... that's why I'm training!
My problem is pretty basic ...
1
vote
0answers
187 views
How to model an accelerometer measurements on a car wheel?
I am working on kinematically modelling an accelerometer on a car wheel.
When working on the initial conditions, I am confused whether or not I should use the gravitational acceleration since there ...
