# Tagged Questions

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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### Position, Velocity And acceleration relations

Today we showed our physics teacher our code for a basic physics engine. He told us that this code snippet is incorrect: ...
1k views

### Zero velocity and non-zero average acceleration

Can you have a zero velocity and nonzero average acceleration? I am confused with the word "average" here. If the question would be, "Can you have a zero velocity and nonzero acceleration?" my answer ...
448 views

### How does angular momentum affect the trajectory of a projectile?

I am thinking about a football thrown in a very tight, very fast spinning spiral. If the football is thrown upwards at a high angle, is it possible for the football to not turn over at the top of its ...
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### Motion in the gravitational field along a trajectory [closed]

A point particle of mass $m$ is moving in the gravitational field along some trajectory which is described by the function $y=y(x)$, which is in a vertical plane and is continuous. Initial conditions ...
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### Can I use $(v_1+v_2)/2$ to find average velocity? [closed]

An object is traveling from a point $M$ to a point $N$ with a velocity $v_1 = 600 \,\rm km/hr$ and comes back with a velocity $v_2 = 400 \,\rm km/hr$. What is the average speed of the object? Can we ...
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### Speed of a river [closed]

I've got a problem (Sorry if it's too basic). It is: Going upstream in a canoe, the passengers throw an empty bottle. They keep rowing for 60 minutes, and move 2 kilometers upstream. They then start ...
59 views

### Minimum Distance for “Speed of Light Approach”

I tried to calculate the minimum distance between a planet and a test mass for the mass to attain the speed of light on colliding with the planet's surface if it were released from rest at the initial ...
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### Motion in 2 dimentions relating $\delta x$ to $\delta y$ [closed]

In a self exercise i was trying to solve this users question what is the initial velocity if angle and range is given? My aim is 1) not to use the standard equations of motion but rather calculus; 2)...
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### Definition of a symbol $s_{NN}$ appearing in particle physics

What is the meaning of $s_{NN}$ in particle physics? See e.g. here http://www4.rcf.bnl.gov/brahms/WWW/thesis/karabowicz_phd_thesis.pdf page 18 in the pdf. What is its relation to energy? I need ...
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### a question regarding relative velocity

"Consider a gravity-free hall in which an experimenter of mass $50~\text{kg}$ is resting on a $5~\text{kg}$ pillow, $8~\text{ft}$ above the floor of the hall. He pushes the pillow down so that it ...
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### Is rate of change of velocity wrt distance and rate of change of velocity wrt time the same thing?

Is rate of change of velocity wrt distance and rate of change of velocity wrt time the same thing?If both are same can we define acceleration in the former way? Please explain using calculus.
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### Height of building [closed]

How would I find the height of a building? I have been given the initial velocity, the angle at which the object was thrown, and the landing distance. And I was able to successfully compute the ...
635 views

### Kinetic energy of an expanding sphere [duplicate]

In the study of Newtonian stellar structure, Weinberg (1972) writes The uniform dilation of a sphere with uniform density will give it a kinetic energy $$U=\frac{3}{10}M\dot R^2$$ I don't ...
561 views

### Hockey puck collision [closed]

I have a homework question in which a sticky hockey puck traveling at constant velocity parallel to the side of the rink strikes a stationary puck and sticks to it. The angels between centres at ...
156 views

### Can anyone kindly help me with these sign conventions?

Since I have some confusions with the sign conventions , I have finally drawn up the following conclusions . Plz check if the following are correct .... ( I have taken all motions directed upwards as ...
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### Web utility for viewing $x$-$t$, $v$-$t$, and $a$-$t$ graphs

I'm wondering if there exists any utility on the web which displays $x$-$t$, $v$-$t$, and $a$-$t$ graphs for, say, a number of well considered example animations. The utility should allow pausing, ...
294 views

### Modelling an Inelastic Collision

I've attempted to model the inelastic collision between a moving mass and a large stationary object, e.g. dropping an ball on the floor, for analysing the approximate kinematics and heat dissipation ...
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### How do I find the angle with respect to the ground that will cause a projectile launched from the origin to land at the origin? [closed]

Given an arbitrary non-zero constant horizontal acceleration (like a breeze perhaps), how would one find the angle with respect to the ground (x-axis) that will cause a projectile launched from the ...
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### Necessity of the Notion of Work and Kinetic Energy

I've worked through many example problems in my college physics text in the section on kinetic energy and work. I noticed that if the desired quantity is velocity or force, they can be solved entirely ...
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### Equation for Figuring out the Displacement for a Projectile at an Angle

I'm wondering if anybody can simply tell me if there is a simple formula to solve for displacement when you've been given the launch angle and initial velocity? See; http://is.gd/LpT1EA To some, it ...
438 views

### $v^2 = 2ax$ or $v^2 = ax$?

As far as I am aware, $v^2 = 2ax$ is the formula to find the velocity in various questions. If kinetic energy = work, $$\frac{1}{2}mv^2=Fx$$ $$mv^2=2max$$ $$v^2=2ax$$ We use this formula to solve ...
390 views

### Magnitude of the average velocity vector (not the average speed)

Thank you ahead of time for taking to look at this. For this following problem we were given an answer however I am almost positive the given answer is wrong. It doesn't even make sense. So here is ...
312 views

### One dimensional motion problem [closed]

I kept almost 2 hours trying to solve this problem : Two trains are 150 km apart. Train A moves at 50.0 km/hr towards train B, which moves at 30.0 km/hr toward train A on the same track. How ...
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### How to eliminate variable $t$ from the equations to solve this question? [closed]

A ball rolls horizontally off the top of a stairway with a speed of $1.52~\text{m/s}$. The steps are $20.3~\text{cm}$ high and $20.3~\text{cm}$ wide. Which step does the ball hit first? I tried to ...
284 views

### Why do objects seem to move faster (relatively) when they move tangential to the observer?

I've observed this loads of times while travelling, in cars, trains,etc.I can't quite put it in words and therefore I've roughly made a diagram to assist my question. Assume an observer is travelling ...
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### Why isn't jerk necessary?

I've recently thought about the rate of change in acceleration and found out that is exists and is called jerk. I've looked at some questions and answers but i could not understand something in this ...
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### Changing directions with a constant speed?

I'm currently working on a problem in which an object's speed remains the same, but it experiences a change in direction after some time. I'm fairly sure it experiences an acceleration in order to ...
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### Heat wave containing particle and wave like properties [duplicate]

I see heatwaves occur on the road and was wondering if that is visible motion of wave like properties involving particles.
387 views

### Rolling as pure rotation

In my book the following statement was written and I didn't understand it well. Can anyone explain it in a more simple way? Figure 11-6 suggests another way to look at the rolling motion of a ...
3k views

### Why does a plane look like it's slower than a car?

Recently, I was in a car and noticed a plane in the sky. What was interesting was that the plane seemed to go slower than my car because I passed the plane. Is there a physics reason to this?
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### Is it possible for a moving body to have no kinetic energy? If yes, then how? [closed]

An object which is moving relative to your coordinate system has kinetic energy in that coordinate system; it does not have kinetic energy in a coordinate system which is stationary relative to the ...
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### Predicting balls's movement in well due to fluid flow

I am a total newbie in fluid dynamics. In one of my experiments/open project, my experiment setup is as below: a small ball sits in a circular well (has mass density a bit heavier than water), with ...
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No Nobel prizes at stake, but just an idle thought and an idle question. How could one calculate the probability of a flipped coin landing stable on its edge, instead of heads or tails? I assume ...
192 views

### From acceleration to displacement

Hi I am a major in Computer science and this question should be really easy for all the physics geniuses here: I have a set of data points from an accelerometer on a moving object that basically ...