The time rate of change of the position of an object

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770 views

How do I determine a component of relative velocity?

At a particular instant, a stationary observer on the ground sees a package falling with speed v1 at an angle to the vertical. To a pilot flying horizontally at constant speed relative to the ...
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2answers
763 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 120º. Which statement is true about the tennis ball ...
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2answers
757 views

Determining Maximum Velocity of an object traveling horizontally

I'm in the process of working on a physics related game. I'm looking to find the maximum velocity of an object given it's mass and the force acting on it when it is traveling horizontally. I believe ...
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1answer
20 views

Projectile velocity and component $x$ and $y$ velocities

So the equations for the X and Y velocity given $\theta$ and $V_0$ are $V_x = V_0\cos\theta$, and $V_y = V_0\sin\theta$. When I test this with something like 1 m/s and and angle of $45^{\circ}$, I ...
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1answer
62 views

Calculating force of a car [closed]

I'm simulating car cruise system and my results are not making any sense. I have been told that my force formula is wrong but I don’t understand why it is wrong and how I can fix this. Does anybody ...
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1answer
31 views

Difference between short impact and sustained pressure

If I press the wall (with my hand) I feel a little pressure at my hand and I move away from it. If I hit the wall (lets say using the same amount of energy for total work) I feel pain in my hand. ...
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2answers
44 views

Finding out the velocity [closed]

Displacement of an object is related to time $x=at+bt^2-ct^3$ where a, b and c are constant motion.Then the velocity of an object when it's acceleration is zero is given by ...
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1answer
82 views

How to calculate average velocity

The position of an object moving along X-axis is given as $X=a+bt^2$ where $a=8.5\,\mathrm m$, $b=2.5\,\mathrm {m/s^2}$ and $t$ is measured in seconds. What is it's velocity at $t=0$ and $t=2.0$ s? ...
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1answer
38 views

Compute the minimal distance between two points in movement

There are two points, $A$ and $B$ that move according to these laws: $$ \vec{x_a}= 20 -10 t $$ $$ \vec{x_b}= -15 +15 t $$ $A$ moves along the x axis, $B$ along the y axis. I have to compute the ...
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1answer
179 views

Small Animal Terminal Velocity

I recently saw a cat fall probably 100 feet like in this video Cat Falls. It seemed as if the cat reached terminal velocity by the time it hit. Does this mean that cats (and other small animals) could ...
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1answer
77 views

Is there any significance to the negative sign on this speed?

A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #$1$). At a time of $60$ s later the friend catches a bus (event #$2$) If the ...
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1answer
86 views

Relativistic addition of velocities of spaceships

If Spaceship 1 is traveling at speed $.5c$ relative to Earth, and Spaceship 2 is traveling at speed $.3c$ relative to Earth in the same direction, what does Spaceship 2 see Spaceship 1's speed as? I ...
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2answers
95 views

Newton's Second Law

Newton's Second Law tells us that $\sum F = ma$. The vector sum of the forces $F$ on an object is equal to the mass $m$ of that object multiplied by the acceleration vector $a$ of the object. So ...
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1answer
53 views

velocity in inertial and nontial frames

I got confused about the difference between the last term of both pictures. In the first one, we have w x r, but in the second we have w x r underlined. Does anyone have a better explanation? They ...
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1answer
129 views

Finding release angle and final velocity of projectile when the target has a different coordinations [closed]

I am trying to write some codes for auto-snowball mechanism which seems like a regular projectile but instead of hitting the targets on the ground it is going to be able to hit the target in the air ...
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1answer
45 views

Recession of galaxies

when you take such a given galaxy and it is said that you are moving away from us with a speed $v$, what do you mean really? Let me explain: is the galaxy itself which has an intrinsic velocity of ...
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1answer
67 views

Does an aircraft hover at a constant acceleration or varied acceleration?

I have a question that's bugging me. Googling it only made me more confused so I really hope someone can help me clear this. If a plane is flying up and down; or hovering (Like the x-wing scene from ...
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1answer
125 views

Finding an equation to solve for the velocity of a swimmer crossing a river [closed]

Where $\theta=45^\circ$, $d_1=200\:\mathrm{m}$, and $d_2=150\:\mathrm{m}$. I do not know how to combine the following equations: $$\begin{align} t&=\frac{d_1}{v_s\cos(45^\circ)}\\ ...
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1answer
30 views

Shock Absorber - Bus - Not Uniform

Imagine a empty bus/lorry travelling at high speed over the "speed brake", why is that only rear seat is heaved relatively high compared to the fron seat?
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1answer
109 views

Can the phrase “Terminal Velocity” be used to describe non-gravity situations?

According to Wikipedia: [Terminal Velocity] is the velocity of the object when the sum of the drag force (Fd) and buoyancy equals the downward force of gravity (FG) acting on the object. Since ...
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3answers
2k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
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1answer
829 views

Difference between velocity vectors, relative speed

Consider two particles moving in the same direction instantaneously but one of them follows a circular path and one follows a straight path. If I adopt a rotating frame of reference in which the ...
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2answers
2k views

How can I add an acceleration vector to a velocity with a different direction?

I am in my last year of high school and am struggling with some homework. I'm sorry if this question is incredibly stupid, but I simply can't find the answer in my notes. If I have an object with a ...
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1answer
157 views

Vertical velocity to reach a certain point given a flat horizontal velocity? [closed]

Suppose I have two points such as $a(4,6,9)$ and $b(32,5,12)$. If I have a flat velocity pointing $a$ to $b (b - a)$ which has an arbitrarily defined magnitude. Given gravity $g$,how can I calculate ...
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1answer
939 views

Relative Velocity and Momentum

The question is, "A $45.5~kg$ girl is standing on a $140~kg$ plank. Both originally at rest on a frozen lake that constitutes a friction-less, flat surface. The girl begins to walk along the plank at ...
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1answer
279 views

Power, Force Velocity

In any case, if the force and power is constant , does velocity also need to be constant? If no, can you tell me a case. Further can this be extended for non-rigid bodies.
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1answer
286 views

Finding The Resultant Vector [closed]

A plane is flying southeast at 215 km/h. Suddenly there is a wind from the north at 75 km/h. What is the plane's new velocity with respect to the ground in standard position?
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1answer
366 views

Calculating vector of plane resulting from tailwind

In some basic physics homework I have, it asks what the resulting vector would be for a plane traveling at x m/s in y direction that is affected by a tailwind going in z direction at w m/s. How would ...
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3answers
296 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 ...
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0answers
39 views

Breaking the speed of light…? [duplicate]

I know the speed of light can't be broken, but I cannot figure out why the following scenario is not possible. I'm not a physicist myself but I know the basic stuff. Assume you're in a car ...
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0answers
17 views

How to calculate the centerline velocity inside a pipe?

Well, I was reading about fluid-solid/structure interaction models for make a simulation in COMSOL, and in few papers about it [1] I find an expression about the centerline velocity. I understand the ...
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2answers
37 views

Orientation of a rocket going in a circle?

This problem is from my physics homework: A rocket is moving at constant speed in a perfect circle in deep space, far away from any planets or stars. The diagram below shows the circle the ship ...
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2answers
62 views

Converting velocity-time line to acceleration-time?

How would one find where the straight line on a VT graph is on an AT graph? For example in the above image, if I were to convert that into an acceleration-time graph, where on the x-axis would the ...
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0answers
35 views

Velocity in relativity

We just started learning about 4-vectors in my physics class, and I'm a little confused about the relationship between the 4-velocity $U=\gamma(c,\vec{v}),$ and the velocity transformations given by ...
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0answers
38 views

Wave Packets, Group velocity, and Phase velocity [duplicate]

Mathematically, you find that the wave function of a particle $\Psi (x,t)$ moves with the same velocity as the velocity of the particle ($v_{particle} = v_{group}$). Is there a reason why the ...
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0answers
79 views

Solenoid pull force & Velocity calculation

So I am building a circular accelerator (like a slightly oversimplified model version of CERN) as a physics project, and I'm at a dead end. I believe I need to know how to work out differential ...
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0answers
28 views

How to calculate the equation of projectile motion for curved ramps? [duplicate]

Consider the following cases (these are sections): I can find the equation of motion for Case a however I don't know how to deal with Case d. Normally I would need the angle α otherwise I can't ...
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1answer
109 views

Determining fluid flow velocity from experimental volumetric flow rate data

I would be very grateful if someone helps me with my issue. I have a pump pumping water into a tube. My goal is to find velocity of the fluid flow in another tube that will be connected to the first ...
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0answers
82 views

Calculating impact velocity and time with non-uniform acceleration [duplicate]

Here goes: imagine a spacecraft with engines shut off in a free fall towards some celestial body x. let's say the distance to surface is $100 000$ $\text{meters}$. initial vertical velocity is ...
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0answers
28 views

The average value of the the square of Dirac velocity operator

Let's have Dirac velocity operator (the case of the free particle: $$ \hat {\mathbf v} = i [\hat {H}, \hat {\mathbf r}] = \hat {\alpha}, \quad \hat {H} = (\hat {\alpha} \cdot \hat {\mathbf p}) + \hat ...
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0answers
14 views

Did a racer on a “restless” course race at some particular average velocity? (2: Starting gate and finish line being rigid to each other)

Consider two participants, a starting gate ($A$) and a finish line ($B$), in a (sufficiently) flat region, both undergoing uniformly accelerated motion, such that $A$ finds constant ping duration ...
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0answers
20 views

Did a racer on a “restless” course race at some particular average velocity? (1: Starting blocks, finish line moving uniformly wrt. each o.)

Consider two participants, $A$ and $B$ moving uniformly wrt. each other; first having approached each other, then having met and passed each other, and eventually having separated from each other such ...
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0answers
42 views

Determining impact velocity over long distances [duplicate]

Everything I have found concerning impact velocity from a given height deals with constant acceleration due to gravity. I would like to know how to work in varying acceleration into the equation. So, ...
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0answers
53 views

Graph of Lorentz force in function of angle between v and B-field?

I need to draw a graph of the magnitude of the Lorentz force in function of the angle between the velocity and B. Am i right in supposing this will be a sine wave?
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0answers
279 views

Gravity change as a function of time only

Is it possible to find how gravity changes with time? That is, height is not part of the equation. For example, $g$ can be expressed as a function of height that does not involve time with this ...
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1answer
612 views

Phonon dispersion calculation based on velocity autocorrelation function in reciprocal space?

I would like to ask about the method of calculating phonon dispersion relation. Up to my knowledge, there are 2 methods to calculate the phonon dispersion: By diagonalizing the dynamics matrix. ...
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1answer
393 views

Deriving the group velocity of a wave produced by some basic cosine waves with unequal amplitudes

Consider some basic cosine waves of the form ${E_i} = {E_0}\cos ({\omega _i}t - {k_i}z)$ with different amplitudes, frequencies and phases. We know a combination of such waves could result in a wave ...
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1answer
280 views

Simple Acceleration Problem throwing me off

I am having trouble with this problem from my homework. I have gone over it many times, and I must have some concept wrong. A rocket is launched from the ground with constant acceleration. After 4 ...
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0answers
66 views

Where does the transformation of $\gamma$ come from?

I was reading Tipler, and in his book he says that in order to transform energy, we must write gamma in terms of quantities in the non-primed frame. However his derivation makes no sense to me, it's ...
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0answers
68 views

Outflow for fluid simulation based on “Stable Fluids”

I've implemented a fluid simulation based on the paper Stable Fluids. It works quite well, except I would like to have the velocity at the "upper" edge just to outflow and not to re-enter on the ...