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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3answers
174 views

Projectile motion formulas

Assuming: The equations for the vertical and horizontal components of my initial velocity. Are: $v_{x,i} = v_i \cos\theta$ and $v_{y,i} = v_i \sin\theta$ And the displacement components are ...
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0answers
41 views

prediction of a moving object

OK, this may be a hard question to answer and really all I am looking for is an equation as I don't even know what to call this. This is all for a game so bare with me please. In the game two ...
7
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4answers
577 views

Integrating radial free fall in Newtonian gravity

I thought this would be a simple question, but I'm having trouble figuring it out. Not a homework assignment btw. I am a physics student and am just genuinely interested in physics problems involving ...
1
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2answers
168 views

Increase in velocity by loss of mass? [closed]

A trolley of mass 300kg carrying a sand bag of 25kg is moving uniformly with speed of 27km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at ...
1
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2answers
282 views

I don't understand the idea of perpendicular vectors being independent of each other?

So problem 71-75 is about vectors. The problem says: A river has a current flowing with a velocity of 2.0 meters per second due east. A boat is 75 meters from the north riverbank. It travels at ...
2
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3answers
110 views

Why isn't centripetal acceleration considered in this problem

Fairgoers ride a Ferris wheel with a radius of 6.00 m. The wheel completes one revolution every 30.0 s. If a rider accidentally drops a stuffed animal at the top of the wheel, where does it land ...
6
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1answer
71 views

What is “kinematic inversion” (from geophysics) in mathematical terms?

I am a mathematician working on a seismic imaging problem, and am currently (attempting to) read some geophysics papers (this one (Ruiz, Madariaga 2011) and this one (Di Carli, Francois-Holden, ...
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1answer
522 views

Why there is a $\frac{1}{2}$ in the distance formula $d=\frac{1}{2}at^2$?

I'm preparing for my exam, but I have difficulties in perceiving why there is a $\frac{1}{2}$ in the distance formula $d=\frac{1}{2}at^2$?
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2answers
56 views

Relative velocity decomposition

In my fluid dynamics course notes is stated a change in relative velocity can be decomposed: $$\delta \mathbf{v} = \left\{ \begin{pmatrix} \Delta & 0 \\ 0 & \Delta \end{pmatrix} + ...
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1answer
74 views

Why does a difference in approach to projectile motion yields different results?

A body is projected vertically upwards from the surface of the earth with a velocity equal to half the escape velocity. If $R$ is the radius of the earth, then find the maximum height attained by the ...
-1
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2answers
51 views

A block in motion explodes [closed]

A 9.5 kg block (A) is traveling in the positive x-direction with a speed of 3.0 m/s. At some point, it explodes and breaks into two pieces. After the explosion, block C, which is 6.0 kg, moves off ...
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2answers
86 views

How to find time, acceleration under this situation

I am trying to solve the following. An object of mass $m$ slides on a horizontal surface with initial velocity $v_0$. If the kinetic friction between the object and mass is given by $\mu$, find ...
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2answers
311 views

Conservation of linear momentum magnitude along a trajectory

I was once criticized for "taking angular momentum as momentum going in a circle". I was loosely trying to state, in classical mechanics, that in using conservation of momentum, one can switch between ...
3
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3answers
502 views

How do I meaningfully divide by a vector?

How long does it take a baseball with velocity $(30, 20, 25) m/s$ to travel from location $r_1 = (3, 7,−9) m$ to location $r_2 = (18, 17, 3.5)m$? I am thinking that it should be the ...
-4
votes
2answers
65 views

How many years would it take the Pioneer space probe to travel to Proxima Centauri with its current speed? [closed]

Pioneer space probe moving at a speed of $30km/s$. Assuming its heading for Proxima Centauri, which is situated at $4.2ly$ from earth, calculate how long it would take to get there in years, to the ...
2
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1answer
161 views

Dog running after sephard

Assume there is a dog A on a field and a sephard B. B moves on straight line with constant ...
2
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2answers
91 views

Relative velocities of boats and a stone thrown by the boat [closed]

Question: A police boat is chasing a boat with criminals along a straight river by moving against the stream. The speed of the river stream is 3 miles per hour, the speed of the boat with ...
2
votes
1answer
85 views

Integration on a general equation for instantaneous angular acceleration

An equation for instantaneous angular acceleration is given as: $$ \alpha \equiv \lim_{\Delta t\to0}\frac{\Delta \omega}{\Delta t} = \frac{d\omega}{dt} $$ The text I am reading says writing this ...
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1answer
112 views

Write a parabolic equation in kinematics

How might I go about writing a parabolic equation in standard form $ax^2 + bx + c$ given all of the following measurements: $X_0, X_f, Y_o, Y_f$: the initial and final x and y positions. ...
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1answer
59 views

Homework - Mechanics [closed]

Just started mechanics and I'm not sure what I'm doing wrong on a question. Car accelerates uniformly from a speed of $50\: \mathrm{kmh}^{-1}$ to a speed of $80\: \mathrm{kmh}^{-1}$ in $20$ ...
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0answers
57 views

Deduction of relativistic mass formula in 1+1 dimensions

I have read the explanation/calculation of relativistic momentum and relativistic mass in the Feynman lectures, see chapter 16.4 here: http://www.feynmanlectures.caltech.edu/I_16.html. (I guess this ...
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2answers
91 views

Relative velocity of boat

I am trying to understand fully the following question: A boat is traveling west at 100m/s and is partially helped by a strong wind blowing at 20m/s 30 degrees north of west. What speed could the ...
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1answer
132 views

Missing centrifugal acceleration

I am trying to get correct equations for acceleration of a point in reference frame A, given position, velocity and acceleration in rotating reference frame B. Let $\mathbf{x}_A(t)$, ...
2
votes
1answer
69 views

Relative motion of airplane in the wind [closed]

I have a relative motion problem in which I cannot get my answer to match the book answer. The question is: An airplane has to travel $189\, \mathrm{km}$ due east to point $B$ from point $A$. It ...
2
votes
1answer
130 views

Is there a better, faster way to do this projectile motion question? [closed]

The question is In a combat exercise, a mortar at M is required to hit a target at O, which is taking cover 25 m behind a structure of negligible width 10 m tall. This mortar can only fire at an ...
0
votes
1answer
167 views

Vector Maths to Simulate Car Physics [closed]

I'm working on a 3D program that involves controlling a Cube on-screen (which represents a car). I use C++, OpenGL and GLM (for vector and matrices etc, if you're familiar with programming; Once the ...
1
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1answer
798 views

Calculate Mass based on Velocity and Acceleration

I am attempting to design a obstacle avoidance system with the Arduino. My position (for now) is going to be stationary. I will be detecting an incoming object and I want to use the below known ...
4
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2answers
112 views

Work done on stationary rocket

Suppose I have a rocket thats exerts a force (with negligible loses in mass), which cancels out the downward force of gravity. Clearly my rocket could be moving at a constant velocity (ignore air ...
0
votes
1answer
135 views

Distance formula in kinematics?

I've always seen it $d = v_i t + \frac{1}{2} at^2$ However, I also saw it as $d= d_i + v_i t + \frac{1}{2} at^2$ where $d_i$ = initial position. This was applied to 2D kinematics. Can anyone explain ...
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2answers
445 views

If I lift a box vertically, why is the work I do equal to the distance I lift it times the force of gravity on the box? [duplicate]

I have problems fully understanding the concept of work, so please forgive me if this is simple. If I take a box of mass $ m $, and lift it a distance $ d $ vertically, why is the work I have done ...
0
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3answers
771 views

Finding Distance an Object Travels Up an Incline After Launch

I've been doing a review for an introductory physics course final. I have a question on one problem though. Here is the problem: A mass (M=2kg) is placed in front of a spring with k=900N/m, ...
1
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1answer
209 views

I am unable to combine two equations in kinematics

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 ...
2
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1answer
67 views

Applying kinematics issue

I've been having an unusually difficult time solving kinematics problems in comparison to all the other students in the classroom. It appears that I'm one of the unfortunate people with an anti-math ...
1
vote
2answers
451 views

Determing time to complete known distance with constant acceleration [closed]

Answer: $a=v^2/d$ is the formula I needed. This is a problem in a programming assignment, I haven't taken physics. I have a starting speed (0 m/s), an final speed (208.33m/s) and the distance it ...
0
votes
3answers
2k views

Calculate average acceleration without time? [closed]

I have a question about a flea jumping, for which I need to show that the average acceleration is around 1000 $ms^{-2}$. I know that to calculate average acceleration you can use $\frac{dv}{dt}$, ...
1
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1answer
40 views

when to consider linear kinetic energy and when to use angular kinetic energy?

I saw a problem about a pivoting rod online (http://dev.physicslab.org/Document.aspx?doctype=3&filename=RotaryMotion_RotationalDynamicsPivotingRods.xml), I am thinking the problem if we initially ...
7
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5answers
10k views

How to get distance when acceleration is not constant?

I have a background in calculus but don't really know anything about physics. Forgive me if this is a really basic question. The equation for distance of an accelerating object with constant ...
2
votes
3answers
2k views

Kinetic energy and momentum conservation in an explosion?

My physics book says, "A firecracker sliding on ice has the same total momentum before and after it explodes." I understand this part. This is because of Newton's 3rd law, and no external forces. This ...
8
votes
2answers
252 views

What is the physical meaning of $|f''(\xi )|\leq\frac{4(f(b)-f(a))}{(b-a)^{2}}$ where $f(t)$ is position as a function of time?

Here is the full problem: I was able to prove the given expression; but the interpretation part is giving me a bit of trouble. Here is my interpretation: The average acceleration in $(a,b)$, is ...
1
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1answer
1k views

How do you calculate instantaneous velocity in projectile motion?

An object is thrown horizontally with a velocity of 30 m/s from the top of a tower. It undergoes a constant downward acceleration of 10 m/s2. The magnitude of its instantaneous velocity after 4.0 ...
0
votes
1answer
75 views

x-coordinate of the ball when it's velocity is perpendicular to projection velocity

We have a ball projected at 20 m/s at an angle $\pi/6$ from the x-axis. Now we have to calculate x-coordinate of the ball when it's velocity is perpendicular to projection velocity. I am thinking ...
-1
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2answers
287 views

Calculate the acceleration of a moving elevator [closed]

An elevator is moving down with uniform acceleration. A man inside the elevator who wants to measure the acceleration drops a coin as soon as the elevator starts. The coin is 6ft above the floor of ...
1
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2answers
2k views

Why do far away objects appear to move slowly in comparison to nearby objects?

When we are sitting in a moving train than nearby stationary objects appear to go backwards...in terms of physics we can use the formula velocity of object with respect ...
0
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0answers
107 views

Calculating journey time of a spacecraft from one planet to another planet

I don't know if this is the correct place to ask =/ I have been trying to make an animation of a spaceship travelling from one planet to another. The animation being this: ...
1
vote
1answer
65 views

Objects falling on Slopes [closed]

An object falls on a slope and then rebounces....and it is known it hits the slope again...how do I calculate it's second point of contact with the slope....how can a projectory equation be used in ...
0
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1answer
95 views

Why do I get inconsistent answers with the kinematics equations?

The initial velocity is 14 m/s the final velocity is 0. The distance is 9.0 m and the time is 1.5 s. When solving for the acceleration, why do I get different values when using different kinematic ...
1
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1answer
74 views

Basic vertical projectile motion

A ball is thrown from the top of a tower with a certain initial speed. It's downward acceleration is g. But why? the initial force makes no difference? and, if not, if I get a revolver and shoot down, ...
0
votes
1answer
150 views

Muon 3 Body Decay

I'm trying to calculate the maximum energy of the electron in the decay muon >electron + electronantineutrino +muonneutrino in the reference frame of the muon having no kinetic energy. $m_m$=mass of ...
0
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2answers
49 views

How to get $t$ from $a(v)$?

I read what if we have acceleration given as a function of velocity we can calculate time as $$t(v) = t_0 + \int_{v_0}^{v} \frac{dv}{a(v)}.$$ Why?
0
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2answers
694 views

Homework Question Transformation Energy [closed]

A $1400kg$ car is approaching the hill shown in the figure at $14.0m/s$ when it suddenly runs out of gas. What is the car's speed after coasting down the other side? I think I have to use this ...