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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2answers
37 views

How can I calculate the change in velocity? [closed]

"A runner runs at 4 m/s on a circular track constantly. A and B are opposite points on the track, so A is the starting point and B is halfway around the track. Calculate his change in velocity from A ...
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0answers
29 views

Particle Disintegration Range of Angles (Landau& Lifshitz)

In the particle disintegration problem in the book by Landau and Lifshitz (pg 44 question 3), it is asked to find the range for $\theta=\theta_1+\theta_2$, where $\theta_1$ and $\theta_2$ are the ...
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3answers
131 views

Find time-parametrization given path and speed of a particle [closed]

Consider a particle in two dimensions with position vector $r(t)=<x(t),y(t)>$ and the shape of the path is described by a function $y(t)=f(x(t))$ (Thus $r(t)$ is a parametrization of $f$ with ...
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2answers
93 views

How much energy is needed to move an object in lossless environment?

How much energy is needed to move a 1 kg object for a distance of 1 meter horizontally in a constant speed (assuming no energy is wasted)? Does it matter what is the movement speed (assuming not ...
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0answers
11 views

Kinematic equations of a cascading particle decay

This paper discusses different measurable quantities that can be used to search for unknown particles at particle accelartors. For the following decay it introduces the invariant mass $m_{XY}$: It ...
1
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1answer
130 views

Understanding rotational motion on a rough surface

I am having trouble gaining an intuitive understanding of rotational motion for an object rolling on rough surface, and I have a few questions regarding it. Let's say that there's a cylinder that ...
2
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5answers
155 views

Pushing down on the gas pedal of a car a good example of jerk?

I'm trying to think of the clearest examples to demonstrate the concept of jerk to a layman. Ignoring drag and making other reasonable assumptions (friction is conveniently there to only allow you to ...
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4answers
336 views

Is $\left|\frac{d\vec{r}}{dt}\right| = \frac{d|\vec{r}|}{dt}\;$?

Is magnitude of instantaneous velocity same as instantaneous speed? More specifically, is $$\left|\frac{d\vec{r}}{dt}\right| = \frac{d|\vec{r}|}{dt}\; $$ Also Is it wrong to say that ...
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0answers
36 views

How does the ball move? [closed]

A lift is moving up with a constant velocity. The passenger in the lift throws a balls horizontally with constant velocity. How will the ball appear to move for a person standing outside the elevator. ...
33
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6answers
863 views

Motion described by $m \frac{\mathrm{d}^2 x}{\mathrm{d}t^2}=-k\frac{\mathrm{d}^{\frac12 }x}{\mathrm{d}t^{\frac12}}$

What kind of motion would a (preferably dimensionless for simplicity) body do if the force acted on it was proportional to the semi-derivative of displacement, i.e. $$m \frac{\mathrm{d}^2 ...
1
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1answer
28 views

Trying to find out how to calculate how fast something moves from the force [closed]

In our introductory physics class (8th grade) I/we would like to find out how fast a piece of paper needs to be moving to break a chopstick. [Similar to putting a straw through a potato] We will be ...
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2answers
59 views

Obtaining Velocity from Acceleration

I'm following a research paper (PDF via RG), part of which is about using the accelerometer of a smartphone to assist the user's positioning via WLAN. Accelerometer is used to determine if the user ...
3
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2answers
13k views

Area under a displacement graph

If the area under an acceleration-time graph denotes velocity and the area under a velocity-time graph denotes displacement, what exactly does the area under a displacement-time graph denote?
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0answers
53 views

Circular Motion: Rubber Stopper Lab

During a lab I was doing involving uniform circular motion, we had to spin a rubber stopper horizontally via a rope. At the bottom of the rope, there was some weights. I have to answer this question ...
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2answers
100 views

Calculus versus Algebraic Kinematic Equations

Deriving the first equation of motion using either algebra or calculus you get the exact same thing, but my knowledge was that you use integral calculus in physics when you have a varying variable, ...
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1answer
43 views

Deriving some uniform circular motion equations

My question basically boils down to this. How do we derive these relationships. 1.)What is the relationship between radius and centripetal force? (inverse, but why?) 2.)What is the relationship ...
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3answers
60 views

Initial speed in homework problem [closed]

This is a homework question. I tried to solve it, but failed. I had to translate this question, so please forgive me if it is poorly worded. In this question you can ignore the atmospheric ...
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votes
1answer
63 views

Vectors and Scalars [closed]

How is Momentum $mv$ integrate form a Vector product to produce a Scalar [ Kinetic Energy $(1/2)mv^2$]? Is this mathematical proof of the vector to scalar change in Absolute Calculus, Number Theory, ...
1
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1answer
37 views

Calculating offset when crossing a river with speed profile [closed]

I am having some issues putting the theory I learned into practise. We have an exercise, that goes as following: A swimmer wants to cross a river with width b. The swimmer heads straight to the other ...
1
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2answers
80 views

The acceleration of the centre of mass [closed]

Given two balls that are thrown straight up in the air at a speed of $40 \:\mathrm{m/s}$, $0.10 \:\mathrm{s}$ apart. One ball is twice the mass of the other. The heavier ball is thrown second. ...
-2
votes
2answers
47 views

Why is it that when I do some substitution, I get $p=1$ for a photon? [closed]

I know that this is wrong, but where did i make a mistake? I just use a few equations and substitutions and I get that the momentum of a photon is one. Here is my math: $p=h/λ$ $p=hf/c$ (substituted ...
2
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2answers
534 views

Why the photon can't produce electron and positron in space or in vacuum?

$$\frac{hc}{\lambda} = K_e + K_p + 2m_e c^2$$ could be the energy conservation equation for a photon of wavelength $\lambda$ decaying into a electron and positron with kinetic energies $K_e$ and $K_p$ ...
2
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2answers
2k views

Pair production - mathematically?

Allover the web i am only seeing a statement similar to this: Pair production is not possible in vaccum, 3rd particle is needed so that conservation of momentum holds. Well noone out of many ...
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1answer
29 views

What is the Kinetic energy of two objects as viewed from their center of mass [closed]

A body of mass $m$ moving with velocity $v$ is approaching the second object of same mass but at rest. The kinetic energy of two object as viewed from their center of mass is: (a)$mv^2$(b)$\frac 12 ...
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0answers
18 views

estimate the launch point and expect the place falling of a shell in the air

suppose that we have a shell in the air, and detected by a particular radar, how do I estimate the launch point and expect a place falling and time will takes to reach its target? I want help please! ...
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3answers
52 views

Net Force On An Object

If 5 different forces are acting on an object in the same direction, is it possible for the net force to equal 0? Could Friction or Gravity make this possible? If so then how?
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2answers
110 views

Problem regarding bullet penetration [closed]

Which property remains constant when we say that bullets are penetrating the wall? I mean is the resistive force always constant for a given wall (assumed stationary and immovable) irrespective of the ...
0
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1answer
41 views

How do you interpret definite-integrating of both sides of an equation?

Consider a particle is moving at an acceleration of $a=f(s)$ [$s$ stands for particle's location) if we have the initial velocity of a particle then what is the final velocity? So... we know that ...
-1
votes
1answer
57 views

2D Kinematics and Projectile Motion [closed]

In this page, I have finished most of the problems. Some of them I am unable to figure out. For 3 a-j, is it possible to solve this problem given parts a and b, that is, can I solve these problems ...
3
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9answers
839 views

Can velocity be an undefined quantity?

We have the image below displaying the uniform velocity by time-distance graph. At every point velocity is constant but what if distance and time both become zero as at origin in the graph is? The ...
1
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4answers
201 views

My physics teacher gave us this equation $v= -3 +3t$

She asked us if the body was accelerating or slowing down, and I immediately said that it was accelerating (because the $a=3>0$). Then she said that I was wrong because the direction of the ...
0
votes
1answer
69 views

Trajectory of a projectile in a three dimensional space [closed]

$g$: the gravitational acceleration—usually taken to be $9.81\:\mathrm{m/s^2}$ near the Earth's surface $θ$: the angle at which the projectile is launched $v$: the speed at which the projectile is ...
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4answers
166 views

Motion caused by Internal force

I would like to clarify whether an internal force in a system can cause it a motion externally? My Physics teacher and also other tuitions in my area tell that only external forces can cause motion of ...
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0answers
24 views

Calculate the parabollic trajectory

In order to calculate the parabollic trajectory (or ballistic) I need intrinsic equation. Now I need to integrate this equation but I don't know how. I would appreciate so much if you help me!
2
votes
1answer
33 views

Kinematics equations: wrong place value [closed]

A marble is launched horizontally off a 93.0 cm high table causing the marble to land on the floor 1.85 m from the base of the table. a.) How long was the ball in the air? b.) With what velocity must ...
-1
votes
4answers
132 views

How do I use the kinetic energy formula using mass as lbs and velocity as mph?

I understand that the formula for kinetic energy is: $(1/2)mv^2$, which is equal to 1 Joule or 1 N-m. If I want $m$ to be my weight (say 150lbs) and $v$ to be 40mph how do I apply it to this formula? ...
3
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2answers
51 views

What are the Kinematics of an Irregular Tripod?

It is a common maxim (at least within the Scouting community) that a triangle is the most stable shape. In practice this means structures should have three legs whenever possible, and have cross-bars ...
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0answers
43 views

The angle of a rifle to hit a target (How to make approximations to find numerical answers) [closed]

The specific question is this: A target appears at a distance of 1250m with the centre of the target 1.2m above ground level. If the sniper was firing from the prone position, the tip of the ...
1
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0answers
13 views

Newton's Third Law? [duplicate]

I've recently met with this new law and the way my teacher worded is so off for me. Shouldn't the equal and opposite reaction cancel out the action because they are equal? Apparently not? Why?
0
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1answer
65 views

Solve for launch angle in projectile motion equation

I need help solving the projectile motion equation for $\theta$. The projectile motion equation is $$ y = \tan(\theta)x - \frac{gx^2}{2v_0^2\cos^2(\theta)}. $$ How do we solve it so that $\theta$ ...
-1
votes
1answer
26 views

Finding the distance travelled during change in velocity from $v_i$ to $v_f$ [closed]

A constant power is applied to a particle of mass m. The velocity of the particle increases from $v_i$ to $v_f$. We have to find the distance travelled by the particle during this interval.(neglect ...
2
votes
2answers
2k 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 ...
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0answers
93 views

Can a pair of members of a “rotating system” be characterized by one value of displacement magnitude?

There seems to be a claim (cmp. Goldstein, "Classical Mechanics", eq. (4-126); or also perceptable here) that values of "velocity", and of "speed", of some participant, say $P$, can not only be ...
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2answers
507 views

Instantaneous Centre of Rotation

Let's say a body is undergoing both rotational and translational motion. I know that ICR of the body as a whole will be the point about which the body is doing pure rotation, so basically will be the ...
-1
votes
1answer
175 views

Rocket projectile motion problem [closed]

I'm not really sure where to start with this question: In a brisk wind from the south-east of $14.1\:\mathrm{m/s}$ a rocket pointed due north is launched from a cliff that is $500\:\mathrm{m}$ above ...
11
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3answers
2k views

Why collide a moving particle with a particle at rest, rather than two moving particles?

I was just reading some lecture notes about relativistic and quantum mechanics, and in the later part of this page the author demonstrates that any relativistic particle collision in the "lab" ...
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1answer
35 views

Calculate the distance of a falling object and terminal speed [closed]

I have a homework problem that I would like to verify that I am doing it correctly. If anyone could help me see where I'm going wrong with the steps, I would really appreciate it. (a) Consider a ...
0
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1answer
74 views

Why does $v^2=cad$ by dimensional analysis rather than $v^2=ad$? [closed]

Constants are generally added in functions to adjust for when magnitudes don't contain information necessary to the accuracy of the equation. Why is it that $v^2=cad$ instead of $v^2=ad$? What ...
-1
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1answer
45 views

I do not know whether i have solved this correctly. Can anyone help? [closed]

A cart is moving along the $x$-direction with a velocity of $4 \;\mathrm{m/s} $. A person on the cart throws a stone with a velocity of $6 \mathrm{m/s}$ relative to himself. In the frame of ...
0
votes
1answer
53 views

Differential equation for velocity regarded as a function of distance [closed]

Given a differential equation for velocity, $dv/dt + v = 1$, as well as its solution, is it possible to derive a differential equation for velocity with respect to distance? I found a solution to the ...