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
123 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 ...
-4
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1answer
181 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?
1
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2answers
250 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 ...
0
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2answers
223 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
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1answer
80 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
56 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 : $$\...
8
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3answers
6k 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 ...
0
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3answers
286 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 ...
0
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2answers
128 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 ...
2
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2answers
258 views

How to find Tangential/Radial/Angular Velocity for motion in any curve?

Is the radial velocity responsible only for changing distance between objects and the component perpendicular to it only for change in direction? If so why? Please try to give a different explanation ...
1
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1answer
37 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 ...
0
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2answers
57 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 ...
0
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1answer
84 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 < ...
0
votes
1answer
365 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 ...
1
vote
2answers
153 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 -------------------------- ...
0
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1answer
130 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 ...
0
votes
1answer
59 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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votes
0answers
43 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 ...
2
votes
1answer
164 views

The norm of the vector sum of two 4-momentum vectors before and after pair production

Two photons traveling along the x-axis (in a lab frame of reference) of different frequencies are about to collide. Their 4-momentum vectors are (h$\nu_1$/c , h$\nu_1$/c , 0, 0) and (h$\nu_2$/c , -h$\...
0
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0answers
46 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 ...
0
votes
2answers
281 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 ...
0
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3answers
156 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 ...
0
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1answer
171 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 ...
1
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0answers
60 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 ...
1
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1answer
240 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 ...
0
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0answers
70 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 ...
1
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1answer
164 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 ...
0
votes
1answer
54 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, ...
0
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1answer
305 views

Methods of solving relative motion questions using algebra or calculus

I am looking for algebraic methods (that may involve calculus) to solve problems of course needed for closest approach and shortest distance apart. I understand that geometric methods are often much ...
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votes
1answer
694 views

Can an object have 0 acceleration because its instantaneous velocity is 0? [duplicate]

If an object has an instantaneous velocity of zero, does this mean that its acceleration is zero?
2
votes
3answers
557 views

Basic question about acceleration [duplicate]

Very basic question. Please show where I'm wrong in the following reasoning. The movement of an object in function of time could be described as $$ x(t) = v t + x_{i} $$ if velocity is constant. If ...
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votes
2answers
51 views

Can I sum-up time?

If a kinetic process takes 1 second to complete(reach a point), and that process is repeated $n$ number of times, is this formula correct $t_t$=$n\times 1$ = total time in seconds? It's similar to a ...
1
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2answers
3k views

Why can velocity and acceleration be negative?

Why is speed and acceleration negative when $V_1$ of an object is say 150m/s, $V_2$ is 0 m/s and $\Delta d=0.50\,\rm m$? I found the time it takes which is 0.0033s and the acceleration to be 90909.09 ...
3
votes
1answer
348 views

Calculating Kryptonian speed in the movie “Man of Steel”

This is my first question, so I'm not sure if this is the right place to ask but: How would you go about calculating the speed of Kryptonians in the movie Man of Steel (2013)? Specifically, I'm ...
1
vote
1answer
101 views

How to explain this to my sir

We all know that $f = ma$. But for finding displacement, we always use: $$ s = s_0 + ut + \tfrac{1}{2} a t^2 $$ My sir, i don't know why for some reason uses this weird method: $$ F = \frac{ms}{t^...
3
votes
1answer
81 views

Special relativity kinematics problem [closed]

I have this problem in SR kinematics. a spaceship travels near earth at c/2. it shoots off a light-ray at 45deg to its direction of travel (measured in its own ref frame). What is this angle in the ...
6
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3answers
1k views

Is Torricelli's law “wrong” for big holes? - Tank draining problem

Consider a tank full of water with a constant cross-sectional area A1 placed vertically on the ground. Now someone drills a hole of an area A2 in the bottom of the tank, and the liquid starts escaping ...
0
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2answers
101 views

Best coordinate system for Projectile motion [closed]

What is the best coordinate system for describing the projectile motion? Rectangular coordinate system or n-t(normal and tangential) coordinate system.
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votes
2answers
98 views

Finding the initial velocity of projectile [closed]

What is the formula for calculating initial velocity of projectile using the conservation of energy given the mass, height, angle ?
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1answer
61 views

Non zero accetion, varying speed [closed]

Can an object have non zero acceleration without having varying speed? How? Can you explain with an example please.?
0
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2answers
103 views

Derivation of $v=u+at$ [closed]

I read the derivation of $v=u+at$ using integration. The steps are as follows - $$\frac{dv}{dt}=a dt$$ $$dv=adt$$ $$\int dv=\int a dt$$ $$\int dv=a\int dt$$ $$v=at+c$$ My questions are as follows - ...
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votes
3answers
5k views

How to calculate meters per second speed when i have distance in meters and time in minutes [closed]

It might be a simple formula but I want to confirm it so can you please tell me how can I find speed in meters per second when I have Distance = 7720298 meters and total time 320941.03 minutes. How ...
0
votes
2answers
249 views

String wrapping around a motionless cylinder

A particle is connected to the end of a thin, weightless string, which has its other end connected to the cylinder, in such a way that motion of the particle causes the string to wrap around the ...
0
votes
2answers
155 views

Velocity and transfer of energy for a body in free fall

I just need to check if my understanding of the transfer of gravitational potential energy to kinetic energy is correct. Is anything wrong below? Say if a body were suspended at a height h above the ...
0
votes
2answers
747 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? It's ...
2
votes
2answers
495 views

A car with constant speed doing a turn

Let's say we have a car with four wheels and the center of the car has a speed of 50km/h. There is no friction or air resistance. If the car is moving straight each wheel will also have a speed of ...
1
vote
1answer
64 views

Solve $a(t) = g - \beta v(t)$ for $t$

If $g$ is the acceleration due to gravity and $\beta$ is a known value, solve for the time $t$ it takes an object to reach a given velocity if the acceleration of the object is given by $$a(t)...
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votes
1answer
28 views

Which acceleration equations? [closed]

Which equation gives the most accurate answer? $$a=g \sin⁡ α-μg \cos⁡ α\\ a=s/t/t\\ a=2s/t^2 -(2v_0)/t$$ Because i get three different answers. The scenario is a box sliding down on an inclined ...
1
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0answers
76 views

How Burmester's theory converts rotary motion of the crank to linear movement?

I have been studying the mechanism of Klann's Mechanical spider and there it was written that by Burmester's theory it converts rotary motion of the crank to linear movement. I tried searching but how ...