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.

3answers
80 views

Estimate quarter mile time

I need to estimate a drag race quarter mile time given the car's weight, bhp and preferably the drive (FWD, RWD, 4WD). I know $v(t) = ds/dt$ and $a(t) = dv/dt = d^2s/dt^2$, but how can I get the ...
1answer
107 views

Do observers at different speeds perceive other speeds differently?

I was told that if a plane takes less time to travel from the China to US as opposed to the other direction due to rotation of the earth. I suspect this is incorrect however. From this scenario I ...
2answers
278 views

Time and distance where velocity is a function of time

I'm creating a video game set in space in which spaceships travelling between places accelerate until they hit a maximum velocity. They then travel at that velocity until a time when they need to ...
0answers
129 views

Meeting Of 2 People On a circular track [closed]

Two persons are running on a circular track either in the same direction or in the opposite direction, indefinitely. The speed of both of them is given to you. Speed will be positive in clockwise ...
2answers
377 views

Does an airplane's speed include the speed of the Earth?

After take off, does airplane's speed include Earth's movement/speed? Do airplanes turn with Earth movement/rotation?
3answers
362 views

Finding instantaneous speed in MPH given acceleration, RPM and gear ratio

I am still trying to figure out how to (semi) accurately model instantaneous speed after having found acceleration. I have found that at higher RPMs, the resultant acceleration will be lower. I was ...
2answers
836 views

Finding acceleration for a car after finding torque

I am trying to calculate the acceleration of a vehicle after finding the torque $\tau$. Assuming my Horse Power is 130 and my RPM is 1000, I calculated torque as: \tau = \frac{130 \times ...
1answer
114 views

why does perpendicular motion to the direction of someone' s approach does not affect the distance between them

I was reading about the the four turtles/bugs math puzzle Four bugs are at the four corners of a square of side length D. They start walking at constant speed in an anticlockwise direction at all ...
1answer
252 views

Relationship between acceleration, velocity and position

I'm learning some applications for equation of motion. But I'm failing to relate velocity, acceleration and position. If $v=\frac{dr}{dt}$ and $a=\frac{dv}{dt}$, why $a$ is $\frac{d^2r}{dt^2}$ ...
1answer
348 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 ...
2answers
338 views

Finding Distance an Object Travels Up an Incline After Launch

I've been doing a review for an introductory physics course final. I have a question on one problem though. Here is the problem: A mass (M=2kg) is placed in front of a spring with k=900N/m, ...
2answers
316 views

Kinematics - concept question

A child tosses a ball directly upward. Its total time in the air is T. Its maximum height is H. What is its height after it has been in the air a time T/4? Neglect air resistance. Ok so I know that ...
2answers
156 views

Should the cold drink come out of a free falling bottle with an open lid?

If I hold an open bottle and perform free fall, say sky diving, along with it from, say 10000ft, while I'm holding the bottle vertically upwards should the cold drink come out of the bottle? Kindly ...
1answer
11k views

Solving for initial velocity required to launch a projectile to a given destination at a different height

I need to calculate the initial velocity required to launch a projectile at a given angle from point A to point B. The only force acting on the projectile after launch will be gravity – zero air ...
3answers
2k views

Difference b/w Kinetics & Kinematics w/concrete example

(I know whether I understand this or not doesn't matter much to my work & study but am just curious.) I still can't differentiate in my head kinetics and kinematics (similar thread is found but ...
5answers
1k views

Why does work equal force times distance?

My 'government-issued' book literally says: Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
2answers
556 views

What is displacement? Position relative to a reference point or change of position

What is the "official" or most useful definition of displacement in the context of kinematics? There are two common ones: Displacement is the length and direction of a line from a fixed reference ...
1answer
134 views

Looking for a way to simplify a physics formula [closed]

I have the following physics formula: $$d = \frac{1}{2} at^2$$ where d is equal to half (at) squared where: d is distance a is acceleration t is time I need to simplify this to get the ...
2answers
302 views

2D - Kinematics - Linkage System using Vector Algebra

I have this question that I dont know how to solve correctly : My question is, how do I find $V_B$ ? I will find the angular velocities myself, but I want to know the method to get $V_B$ ? I know ...
1answer
1k views

How do kinetic energy and linear momentum relate?

It took me quite a long time to click my gears in place and even then I'm not sure it's completely correct. The problem is that I need to understand these concepts (physics concepts; not just these ...
1answer
140 views

A practical deceleration question

My friend is a U.S. Army paratrooper. Today, through an unfortunate series of events, he was jerked out of a C-17 traveling at 160 knots by his reserve parachute. First-hand accounts describe it as he ...
1answer
77 views

A Satellite's Perspective

If a planet is spinning east to west and there is a satellite spinning from west to east... Can the satellite travel at a speed sufficient to make the planet appear, from the vantage point of the ...
1answer
1k views

Question on Projectile Motion equation [closed]

A golf ball is shot into the air from the ground. If the initial horizontal velocity is 20m/s and the initial vertical velocity is 30m/s, what is the horizontal distance the ball will travel ...
3answers
250 views

Differential squared vs. differential of squared

Why it is said that $$\frac{dx^2}{dt^2}=\upsilon^2$$ I can only understand the following one: $$\left (\frac{dx}{dt} \right)^2=\upsilon^2$$ Edit: Excerpt from Landau's Mechanics: Execrpt from ...
1answer
690 views

Trajectory of projectile thrown downhill

I'm teaching myself mechanics, and set out to solve a problem determining the optimum angle to throw a projectile when standing on a hill, for maximum range. My answer seems almost plausible, except ...
2answers
189 views

Find vector position in time give this graph?

Graph is position x position. There are 3 points, $A$, $B$ and $C$. $A(0,2)$ $B(4,2)$ $C(6,0)$ Particle travels from $A$ to $B$ and from $B$ to $C$ at constant $v = 2 ~m/s$. Find vector ...
2answers
123 views

Trains travelling at different speeds towards a station C

Here's the question: Consider two stations A and B located 100 kilometer apart. There is a station C, located between A and B. Now trains from station A and B start moving towards station C at ...
3answers
1k views

Maximum range of a projectile launched from elevation “dumbed down”

I am trying to conceptually understand why the angle which produces the greatest range for a projectile launched with an elevation is not 45 degrees. I have exausted all other options, and I hope that ...
2answers
195 views

What is the displacement of an accelerated and relativistic object?

Displacement in an accelerated classical object is: $$s=ut+\frac {at^2}{2}$$ What is the displacement of an accelerated relativistic object? In Newtonian mechanics there are two types of ...
1answer
1k views

Simple Projectile Motion Question

A volcano erupts 50m below the sea level. A rock leaves the crater at 20 m/s at an angle 30 deg with the vertical line. The rock has a mass of 15kg. IGNORE WATER RESISTANCE. It gets out of the water, ...
1answer
627 views

What's wrong with this equation for harmonic oscillation?

The question: A particle moving along the x axis in simple harmonic motion starts from its equilibrium position, the origin, at t = 0 and moves to the right. The amplitude of its motion is ...
2answers
256 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 ...
1answer
648 views

How do you calculate instantaneous velocity in projectile motion?

An object is thrown horizontally with a velocity of 30 m/s from the top of a tower. It undergoes a constant downward acceleration of 10 m/s2. The magnitude of its instantaneous velocity after 4.0 ...
2answers
210 views

Kinematics Problem

The question asks me to find the angular velocity. Now I do not want you to solve my homework, I want explanation please. It states that the acceleration of point P is \$\vec{a}= -3.02 \vec{i} ...
1answer
578 views

How do I know an initial speed of a thrown object using the max height [closed]

The simulation being referred to is in box2d An object is thrown to the max height of $h$ with gravity of $g$, what is it initial speed? I tried the following: $v = v_0 - g t$ $0 = v_0 - g t$ \$t ...
2answers
299 views

Can these figures demonstrating the safety of “Archery Tag” arrows be correct?

There is a new sport called "Archery Tag" that involves shooting opponents with foam-tipped arrows fired out of a real bow. The official Archery Tag web site presents data that claims to show the ...
3answers
174 views

If my acceleration is -1 ($a=-1\:\rm{m/s^2}$) and I'm standing in the infinite ($x_0=\infty \:\rm m$), could I reach the point $x=0\:\rm m$?

I'm standing in the infinite where $x_0=\infty \:\rm m$. If I have a negative acceleration, could I reach the point $x=0\:\rm m$? Would it be possible to calculate how long would take to reach the ...
1answer
221 views

Calculating the launch angle of a horizontal launch (mechanics) [closed]

I need some help with the following question: A smooth spherical object (the first object) is projected horizontally from a point of vertical height H = 26.38 metres above horizontal ground with a ...
2answers
457 views

What will be the relative speed of the fly? [duplicate]

It has happened many times and i have ignored it everytime. Yesterday it happened again . I was travelling in a train and saw a fly (insect) flying near my seat. Train was running at a speed of ...
3answers
361 views

A freefalling body problem, only partial distance and time known

Well, I've been trying to figure out a problem which I imposed on myself, so no literal values included. Unfortunately, my brain is not cooperating. The problem states: What is the height from ...
1answer
606 views

How to find acceleration given position and velocity?

Sorry for this very simple question but I am still very new to the laws of motion. I am dealing with 2-dimensional vectors in my programming environment and I'm following these slides to learn about ...
1answer
324 views

Question of force of friction on incline plane [closed]

An object of mass $4\text{ kg}$ starts at rest from the top of a rough inclined plane of height $10\text{ m}$. If the speed of the object at the bottom of the inclined plane is $10\text{ m/s}$, and ...
1answer
102 views

Simplifying some math for an ant-on-rubber-band problem

OK, I've been doing this problem for fun (it's a great problem, BTW!): http://www.physics.harvard.edu/academics/undergrad/probweek/prob76.pdf Here is the solution: ...
2answers
368 views

Sign of Velocity for a Falling Object

I'm working on a homework problem in Mathematica. We have to graph the height and the velocity of a function given an initial height and initial velocity. However, when I do the graph for the velocity ...
2answers
766 views

Why do far away objects appear to move slowly in comparison to nearby objects?

When we are sitting in a moving train than nearby stationary objects appear to go backwards...in terms of physics we can use the formula velocity of object with respect ...
1answer
892 views

How to find speed from Newton's law?

I have a question about Newton's law. The question says block A(mass 2.25kg) rests on a tabletop. It is connected by a horizontal cord passing over a light, friction less pulley to hanging block ...
1answer
369 views

The acceleration of a particle moving only on a horizontal plane is given by a= 3ti +4tj, [closed]

The acceleration of a particle moving only on a horizontal plane is given by a= 3ti +4tj, where a is in meters per second-squared and t is in seconds. At t = 0s, the position vector r= (20.0 m)i + ...
1answer
135 views

What is the origin of the naming convention for position functions?

In physics, position as a function of time is generally called d(t) or s(t). Using "d" is pretty intuitive, however I haven't ...
2answers
487 views

Calculating Impact Velocity Given Displacement and Acceleration

Assume a car has hit a wall in a right angled collision and the front bumper has been displaced 9 cm. The resulting impact is 25g. Also, it is evident by skid marks that the car braked for 5m with ...
2answers
74 views

Acceleration: Value Disparity?

If we consider a ball moving at an acceleration of $5ms^{-2}$, over a time of 4 seconds, the distance covered by the ball in the first second is $5m$. In the 2nd second will $5 + 5 = 10m$. In the ...
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