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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Two Dimensional Kinematics and Projectile motion [duplicate]

I have a question. So a baseball is hit with a velocity of 30 m/s at 42.6 degrees to the ground. A fielder who is supposed to catch the ball is smart and knows that he is exactly 8 meters from where ...
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1answer
60 views

Path of wheels of a bicycle

Why are the wheels of a bicycle moving in concentric circles with the center O? I know that the velocity of the back wheel is parallel to the frame of the bicycle and the velocity of the front wheel ...
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1answer
87 views

A question about finding average velocity and average acceleration

I have trouble understanding the following problem's answer: Which of the following relations are true for any arbitrary motion in space? (a) $v_{avg}=\frac{r(t_2)-r(t_1)}{t_2-t_1}$ ...
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1answer
37 views

Horizontal distance covered by an object from an initial height to the ground

We are given: An angle $\theta$ with respect to the ground, its initial height $h_0$ and the final distance $d$. How can we find the initial velocity from this information? I tried a bunch of things, ...
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1answer
84 views

Direction of radial acceleration same in circular motion?

I have a big confusion. There is a question in my book which basically says that a ball is tied to a string and rotated. and it asks me to tell whether the following statement is true of false. ...
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1answer
84 views

Finding resultant and direction of resultant

In this question- A motorboat is racing towards north at 25km/h and the water current in that region is 10km/hr in the direction of 60 degree east of south. Find the resultant velocity of the ...
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1answer
88 views

How to use accelaration data of moving object to calculate distance?

I read couple of similar question on this forum and few blogs on web, though I am still confused,I am determined to calculate object displacement using accelerometer data. So, I tried using ...
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2answers
40 views

Is in this case distance same as displacement? [closed]

I have this graph, and I need to know the displacement in the interval from 0 to 5 seconds, so I found the area of the rectangle that you can see there. A = w*h, which means X = (5 seconds)*(20 m/s), ...
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1answer
62 views

A particle has $\overrightarrow{r}(0)=4m(\hspace{2pt}\hat{j}\hspace{2pt})$ and $\overrightarrow{v}(0)=(2m/s^2)\hat{i}$ [closed]

I am having trouble with these problems, and I want to gain a understanding of how to solve these. I'll put what I have tried at the end, even though I don't think it'll be of help. A particle has ...
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3answers
173 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 ...
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1answer
83 views

Earth moving over the Sun instead of around [closed]

Let's say you are observing the movement of the Sun and Earth from very far away. After year 1, the Earth creates an orbital plane around the Sun. Since the objects in the universe induce forces of ...
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2answers
327 views

Projectiles Launched at an Angle with unspecified Initial Velocity [closed]

I'm attempting to do my Physics homework, and I did the first one right, but that problem gave me initial velocity. This problem gives me only the angle relative to horizontal and the distance it ...
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1answer
61 views

How to calculate the kinetic energy of supernova ejecta?

I believed I could use $0.5\times M_{ej} V_{ej}^2$, with $M_{ej}$ being the ejected mass and $V_{ej}$ being the velocity of the ejected mass. But I noticed in this and this that the the mean velocity ...
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1answer
40 views

Viscosity and Density

So I'm reading my textbook and it says that that magnitude of air resistance $f(v)$ can be given as a taylor expansion: $$f(v) = bv + c^2v = f_{\text{linear}} + f_{\text{quadratic}}$$ The linear ...
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0answers
67 views

Projectile Motion Equation - Understanding this Formula [closed]

I don't understand why this formula is relevant to the problem: This was the relevant worked solution: My problem is that I do not understand this formula because I don't even understand what ...
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2answers
93 views

A problem says : a car starts from rest and undergoes a constant acceleration. It travels 5 m in the…? [closed]

A problem says : A car starts from rest and undergoes a constant acceleration. It travels 5 m in the t interval 0 s to 1 s, find the displacement of the car during the time interval from 1 s to 2 ...
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1answer
55 views

How do you find the average speed and average velocity? [closed]

The shuttle craft "Galileo" travels at a constant velocity of $2.73*10^3$ m/s up for $34.0$ min. and then turns around to travel $1.45*10^3$ m/s down for $15.0$ min. a) Find its average speed. b) ...
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1answer
57 views

About how much force would something have to exert to be effectively unstoppable? [closed]

Assuming an object is moving in a straight line propelled by a force. How much energy would that force have to exert so that there are no known forces or objects that could stop it from moving in that ...
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1answer
86 views

Relative velocity of two cars [closed]

Two cars A and B are at $100\,\text{m}$ and $200\,\text{m}$ distance from the origin $O$ at time $t = 0$. They start simultaneously with velocities $10\,\text{m/s}$ and $5\,\text{m/s}$ respectively. ...
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3answers
203 views

Two runners on two different tracks

I got a question from a textbook, as follows. On two different tracks, the winners of the one-kilometer race ran their races in 147.95 seconds and 148.15 seconds. In order to conclude that the ...
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2answers
3k views

Projectile motion without air resistance [closed]

Does the mass of projectile affect its trajectory when it is projected in no air resistance environment and why?
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1answer
41 views

Ways of finding average accelleration

So I had a little debate with a professor on a simple problem of motion (See section). It basically comes down to how to find average acceleration. I did some research and couldn't find a definite ...
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1answer
45 views

Average acceleration when more than two different velocities occur [closed]

Suppose a car travels at 5m/s north for 5 seconds, it then turn east and travel at 7m/s for 10 seconds, finally it turns north east and travel at 10 m/s for 20 seconds. What is the average ...
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1answer
49 views

Finding Acceleration Force of Gravity on Rotated Accelerometer

Is it possible to calculate the force of gravity on the $x$, $y$, and $z$ readings of an accelerometer if I know the rotation of the sensor? If so, how would I do this? Sorry if I am doing this ...
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2answers
49 views

Problem finding the average velocity [closed]

Problem: A car travels along a straight line for first half time with speed of 40 km/h and second half time with speed 60 km/h. The mean speed of the car is__________. My answer: 48 km/h Why? ...
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1answer
68 views

Gravitational Potential Energy to Kinetic Energy

When a yo-yo is released from a height $h$, the gravitational potential energy is converted to kinetic energy. However, the yo-yo obviously has less acceleration than $g$, $9.8\frac{m}{s}$. This means ...
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1answer
110 views

Forces acting on a double pulley

In a double pulley system, if the mass of the object is 10 kg and the object is accelerating upwards at 2 m/s$^2$, what is the tension in the ropes? I figured the weight of the box is 100N and the ...
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1answer
45 views

Deviation from 2D trajectory

I need to find out how far a ball is from the predicted trajectory in 2 dimensional space and I know the start and end position of the ball in both dimensions. Along with that I know the initial ...
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1answer
84 views

An oscillating skateboard

A half pipe of a skateboard park consists of a concrete trough with a semicircular section of radius 5m, I hold a frictionless skateboard on the side of the trough, pointing down toward the bottom and ...
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3answers
54 views

Perceiving travel speeds from different view points

Scenario: Two vehicles pass each other on a highway moving at 100km's an hour; from a stationary position beside the road you witness these cars pass each-other directly in front of you: from your ...
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1answer
80 views

What do negative times and negative distances represent in parametric projectile equations?

There are negative times and negative x and y distances in parametric equations; what do they represent? And is it possible to tell the object's speed, direction and acceleration from just a ...
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2answers
90 views

What moves an object? Momentum or Kinetic Energy? [duplicate]

What exactly makes an object move? Momentum is $\vec p= mv$ where $m$ is mass of an object and $v$ is the velocity of an object, and as a result of this when I fire a bullet the bullet may travel much ...
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1answer
75 views

Why is the range for a particle thrown at 90 degree same as that of a particle thrown at 0 degree?

There is a derivation given in my book which concludes to the fact that the range is same for two angles of projection, provided they are complementary. I fail to understand this fact. For example, ...
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1answer
43 views

Are Both figures correct? [closed]

Actually I am in high school I just want to confirm that whether two figures of this question possible: Question is : A car is moving along a straight line OP.It moves from O to P in 18 seconds and ...
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1answer
38 views

Simple mechanics problem [closed]

I have no idea how to approach this problem I drew the diagram but that hasn't helped that much.
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2answers
92 views

Kinematic sign convention

For example, if I drop a ball from a $50$ meters building, then I will consider the ground is $0$ meter downward is positive ( which makes gravity positive, downward velocity positive, etc) so ...
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4answers
874 views

How can there be really any instantaneous velocity?

I have read about Zeno's arrow paradox that tells us there is no motion of the arrow at a particular instant of its flight. It can be inferred that there can be no velocity at any instant. Moreover we ...
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1answer
786 views

Distinguish between instantaneous speed and instantaneous velocity

I encountered a line in my text book of physics that: Average speed over a finite interval of time is greater or equal to the magnitude of the average velocity. But instantaneous speed at an ...
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1answer
200 views

Finding dv/dx when given x and v as functions of t [closed]

This isn't a homework question, I tried to word this as a physical problem and it got re tagged as homework by someone Say I am given the equation of position in one dimensional kinematics. Say its ...
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3answers
5k 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 ...
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0answers
25 views

How much (little) wind force does it take to move a toddler in a stroller? [closed]

This question is raised because of the recent incident in a London subway station involving a stroller falling onto the tracks. The stroller was probably 10 feet (or 3 m) from the edge of the ...
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0answers
228 views

What is the angle of projection when at maximum height the speed of a projectile is half the speed at half the maximum height? [closed]

I have been struggling with this problem: The speed of a projectile when it reaches its maximum height is one half of its speed when it is at half its maximum height. What is the initial ...
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3answers
732 views

Calculating vertical velocity component of a particle with mass, given the hit point of parabolic motion

Consider the following situation: I have a particle with a given mass that at a given instant of time (let's say $t_{0}$) is placed at the system origin. The particle has a constant velocity ...
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1answer
95 views

Will A Vertical Projectile Travel the Same Distance as A Horizontal Projectile

If a projectile is fired vertically from an initial height, $h$, above ground level, and an identical projectile is fired with equal initial velocity from the same initial height in the horizontal ...
3
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2answers
171 views

Rotational velocity of face-on spiral galaxies using spectroscopy

I am doing my first steps in spectroscopy (IFS actually) and how we can learn more about galaxies by using it. I came up with a simple question which, unfortunately, I can not answer: How can we ...
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2answers
140 views

What is the relative acceleration of a projectile fired at in a low gravity vacuum?

This question is to end an old argument. Given a (space) vehicle with an acceleration of X, and projectile with an acceleration of 2X (rocket, not bullet), what would the relative acceleration of the ...
3
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3answers
77 views

The motion of the particle satisfies $\textbf{v} = \textbf{c}\times \textbf{r}$

Why does a particle with position $\textbf r(t)$ that satisfies $\textbf{v}(t) = \textbf{c}\times \textbf{r}(t)$ follow a circle that lies in a plane perpendicular to $\textbf{c}$ with centre on a ...
2
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1answer
76 views

Distance along projectile motion [closed]

I was doing kinematics these days, projectile motion. And I did the basic concepts: range, max height, time of flight, projectile on inclined plane. I am curious to know how we would solve a question ...
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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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2answers
99 views

Kinematics problem involving rocket

A rocket is fired vertically and ascends with a constant vertical acceleration of 20 m/s^2 for 1 minute. It's fuel is then all used and it continues as a free particle. Find the Maximum height ...