All Questions
Tagged with motion or kinematics
4,321 questions
2
votes
2
answers
193
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How do kinematic equations work regardless of mass of the object?
I came across this question (very simple):
"A dog is running and starts to get faster at $2 ms^{-2}$ for $3s$. If the dog covers $20 m$ over this time, what velocity did it start with?"
...
- 718
7
votes
4
answers
8k
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Is Torricelli's law "wrong" for big holes? - Tank draining problem
Consider a tank full of water with a constant cross-sectional area A1 placed vertically on the ground. Now someone drills a hole of an area A2 in the bottom of the tank, and the liquid starts escaping ...
0
votes
1
answer
50
views
Time dependence of de Broglie wavelength of an electron with initial velocity $V\hat{\imath}$ and in a uniform magnetic field $B\hat{\jmath}$
I am supposed to comment on the time dependence of de Broglie wavelength of an electron with initial velocity $V\hat{\imath}$ and in a uniform magnetic field $B\hat{\jmath}$.
Obviously since the ...
Buzz♦
- 17.1k
2
votes
2
answers
3k
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How do we implement the speed differential for the Ackermann steering?
I'm working on a vehicle that uses four independent motors to control both the steering and speed for each wheel. I'm using Ackermann steering, and I've already got the steering angles down for the ...
CommunityBot
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-2
votes
3
answers
96
views
Why is it wrong to find centripetal acceleration using change of velocity over change of time?
This question asks to find the centripetal acceleration by giving the initial and final velocity over the change of time.
As shown, my book combined two rules to find the acceleration. I utterly ...
- 213k
1
vote
1
answer
78
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Inconsistency in the $2\to 2$ kinematics
I must be confusing something horribly, because this should be very simple, but I am keep getting inconsistent results in the basic 2->2 scattering kinematics.
Let the process be $$a(p_1) + b(p_2) \...
- 877
5
votes
0
answers
113
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"A stationary ball starts to move along a straight line with velocity $v=2x$." Impossible? [closed]
In my physics assignment, there is a problem which asks me to consider the scenario where
"A stationary ball at the origin starts to move along the $x$-axis with velocity $v=2x$."
($x$ is ...
- 213k
-4
votes
3
answers
92
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How do you prove the formula for momentum? [closed]
I am just an absolute beginner to physics. I've seen a proof of the formula for momentum using Newton's second law of motion, but to prove Newton's second law of motion you have to use the formula for ...
- 3,062
0
votes
1
answer
33
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Calculating the apparent load on a suspension point during deceleration of an object in motion
Ok, so I work in the entertainment industry and deal with hanging scenic elements/lighting/video walls pretty regularly. For reference I do the installation part not the planning so don't get too ...
- 11.2k
1
vote
2
answers
100
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Is it possible to realize a probabilistic Maxwell's demon using Tesla valve?
Imagine a container, with balls of diameter 1x and 10x, moving randomly in all directions. These balls are mixed, so it is a low order system.
Now this container is connected to another container via ...
1
vote
1
answer
1k
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How do you calculate velocity reduction over time due to drag, when drag is also a function of velocity?
The drag equation is: $F_D=\frac12 \rho C_d A v^2$, assuming constant values let's simplify to $F_D=Cv^2$
Assuming there are no other forces to consider, I'm really not sure where to go from here. I ...
CommunityBot
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1
vote
1
answer
87
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About Plane motion [closed]
An excerpt from a book I read:
“In reality, objects are moving in a 3-dimensional space. However, if the acceleration of the object is constant, then there must be a certain plane which contains the ...
- 720
0
votes
1
answer
34
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How to compute the force on a mass traveling along a parametric curve? [duplicate]
Suppose a mass (m) is traveling along a parametric curve {x(t), y(t)} where x(t), y(t) are twice differentiable. What is the centrifugal fore on the mass as a function of time?
I am an engineer, and I ...
- 39.3k
0
votes
1
answer
88
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How to correctly calculate minimum distance with kinematic equations [closed]
Two particles P and Q are initially 40 m apart P behind Q. Particle P starts moving with a uniform velocity 10 m/s towards Q. Particle Q starting from rest has an acceleration $2 m/s^2 $ in the ...
CommunityBot
- 1
0
votes
1
answer
42
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Difference between friction force and force because of friction?
I'm doing some physics studying right now and the wording of an example question really confused me so I was hoping to get help in figuring it out. It says that " The coefficient of friction ...
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-4
votes
1
answer
83
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What is the acceleration experienced by a person walking into a tree or pole?
Please go to this website and view videos of people walking into things. I would like to know what is the deceleration their head experiences from this.
I have done my research on this already. A ...
- 718
4
votes
6
answers
6k
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Does an object move because it has Kinetic Energy or does it have Kinetic Energy because it is moving?
Maybe to explain I'm wondering if an object gains $\rm K.E.$ which causes it to have a velocity or does an object have a velocity which cause it to get $\rm K.E.$?
1
vote
0
answers
33
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What was Grant Holloways top speed in his 12.81s 110m hurdle run using kinematics? [closed]
I am a currently a introductory biophysics student and I am attempting to analyze Grant Holloway's 12.81s 110m hurdle run. I thought the best approach would be to break the run into stages due to the ...
- 213k
1
vote
1
answer
185
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In a uniformly accelerated motion experiment, the acceleration can be attained from $V_{ave}$ vs. $t/2$ and $x$ vs. $t^2$ graph. How is this possible?
Specifically, in the experiment, we had to release a glider from an inclined plane (that had an angle of inclination of 10 degrees). We had to calculate the time it reaches the final position. We had ...
- 363k
0
votes
2
answers
300
views
Doubt in negative sign of relative velocities of two objects in same directions and opposite directions
Consider the following examples.
case 1)Two objects traveling in same direction one A in the velocity say 50 mph and other B in the velocity 60 mph. If we calculate velocity of A with reference to B ...
- 213k
-1
votes
2
answers
5k
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What does speed of an object relative to water mean?
A swimmer swims with the velocity 1.25 m/s "relative to water". He has to swim across the river which is 150 meters wide. If his direction of velocity is perpendicular to the stream, he is taken away ...
-2
votes
1
answer
91
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From where does the expression of the tangential accerelation come from?
I've seen so many times that the expression of the tangential acceleration is known to be: $$a_t=\ddot{s}$$ but from the expression of the acceleration in spherical coordinates, in the tangential ...
- 414
0
votes
1
answer
92
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Why isn't work $Fd \sec \theta$? [closed]
In the following image if force the triangle PAN was right angle at P then the component of force in the direction of displacement would be $F\sec\theta$ so work $F*Displacement(AC)*\sec \theta $.
I ...
1
vote
0
answers
32
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Is the speed of a single gas molecule in a box moderated (is the Maxwell Boltzmann curve narrowed)?
I see the second law of thermodynamics
as an observed law, not an imposed law:
it is broken sometimes on a larger scale
and broken often on a molecular scale.
So, if a box contains only one gas ...
- 11
0
votes
2
answers
56
views
Find deceleration to stop car in perfect position [closed]
I'm running a simulation that updates in a fixed time $dt$.
I have a car moving straight with initial velocity $v_0$. This car has to move exactly a distance $D$ in $t$ seconds (for simplicity, ...
- 51.6k
1
vote
2
answers
205
views
Automobile steering relation
The automobile steered by an Ackerman mechanism has the schematics below. According to the author (Reza N Sazar, Vehicle Dynamics: Theory and Application), the steering angles must not violate the ...
- 1
24
votes
7
answers
10k
views
Can an object *immediately* start moving at a high velocity?
What I mean is, suppose a ball is fired from a cannon. Suppose the ball is moving at 100 m/s in the first second. Would the ball have started from 1m/s to 2m/s and gradually arrived at 100m/s? And is ...
- 14.9k
0
votes
1
answer
1k
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Conservation of energy in a powered rocket landing?
When a rocket goes up some of the energy from burning fuel is stored as gravitational potential energy in it, when it falls back the potential energy is now converted to kinetic energy and heat energy....
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-1
votes
1
answer
66
views
Interpretation of velocity-velocity and acceleration-acceleration curves
I am parametrizing equations of motion in the form:
$$x(t) = x_0+v_{0,x}t\\y(t) = y_0+v_{0,y}t+\frac{1}{2}at^2$$
The parametrized equation with respect to time:
$$y(x) = y_0+v_{0,y}\cdot \frac{x - x_0}...
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-1
votes
5
answers
890
views
Force and Velocity directions
When ever the force and velocity are in thesame direction(0°), an object speeds up. When ever the force and velocity are in opposite directions(180°), the object slows down. Also , when ever force ...
CommunityBot
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3
votes
4
answers
2k
views
Do time dilation and length contraction cancel out?
I've recently been getting into special relativity by myself. I noted something interesting: We know that the factor by which time dilates and lengths contract is the Lorentz factor
$$\gamma = \frac{1}...
2
votes
3
answers
2k
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Would this be correct for kinetic energy in special relativity?
In galilean relativity $$p=mv$$ and $$KE=\frac{1}{2}mv^2$$
If I understand it in special relativity the equation for momentum is $$p=\frac{mv}{\sqrt{1-\frac{v^2}{c^2}}}$$ In galilean relativity ...
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1
vote
6
answers
226
views
How to determine whether an object is a point object?
I know that we can consider an object as point object, if its size is negligible as compared to distance traveled by it in reasonable amount of time. But in my book Ncert there is questions which asks ...
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1
vote
1
answer
92
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Wording of Relative Velocity problems [closed]
I've been doing some relative velocity problems. The three main types I do are to do with cars, boats/rivers and planes/crosswind.
I'm fine with cars as the wording is pretty straightforward - it is ...
- 99.9k
0
votes
1
answer
193
views
Zero acceleration in circular motion while the body is accelerating
I was going through László Holics book (300 Creative Problems in Physics) and came across this question:
The radius of the tire of a car is $R$. The valve cap is at a distance $r$ from the axis of ...
- 176
1
vote
2
answers
194
views
Centripetal acceleration with constant speed
If a particle is moving in a circular path at a constant speed, how can we represent its centripetal acceleration? Since the speed is constant, I assume that the centripetal acceleration describes how ...
- 213k
1
vote
1
answer
185
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Position-time graph of two cars is given [closed]
So this was a test question, I answered that both cars have the same acceleration. Since the graphs for A and B both are straight lines, therefore, the acceleration of both must be zero. But the ...
- 1,554
1
vote
2
answers
103
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How can motion along a spiral curve conclude in a finite time, but have infinite turns around the origin?
The first question of the book "200 puzzling problems in physics" has 3 point objects forming a triangle(equal sides), and they start moving towards one another - A always moves towards B, B ...
- 3,477
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votes
2
answers
2k
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Can power to weight ratio be used to calculate theoretical 0-60 times?
The power to weight ratio is used to calculate how fast a car can accelerate. If a car has 400 hp and a weight of 2000 lbs (400/2000), it should make 0.2 hp per pound. If I switch the fraction around (...
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1
answer
131
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Work done with varying angles
I'm having trouble understanding why work done by a force is calculated in the way as described in the following problem.
I kind of get why the work done by W is just $mgh$:
$ work = U_{1-2} = \int \...
- 77.9k
0
votes
3
answers
406
views
Is Retardation and Deceleration the same thing? [closed]
Does, Deceleration always have to be Retardation? Or, can there be Deceleration without Retardation.
- 99.9k
0
votes
1
answer
78
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To find the displacement of a rolling body
When calculating the displacement of a rolling body do we just calculate the displacement due to Vcom in a particular time t or additionally need to consider also the displacement that may be produced ...
- 77.9k
4
votes
3
answers
9k
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Average Velocity: $( v_1+v_2)/2$
While searching for the answer regarding, why acceleration is needed to be constant for using the formula $(v_1+v_2)/2$ , I found many simple and easy proofs regarding this, here in this Physics.SE ...
- 99.9k
4
votes
3
answers
2k
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"Rigorous" derivation of kinetic energy
I've always wondered where the formula of (non-relativistic) kinetic energy we learn at high school comes from. This is the "derivation" I came up with:
$\Delta W:=\int_{r_0}^{r_1}drF=m\int_{r_0}^{r_1}...
- 11
2
votes
0
answers
80
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Equation of Motion of Rigid Body Represented by Twist and Derivative of Twist
This question is an extension of question Understanding terms Twist and Wrench.
Assuming there is a rigid body with body twist denoted as $\mathcal{V}_{b}=\left(\boldsymbol \omega_{b}, \boldsymbol v_{...
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1
answer
44
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What is the area under the graph for decelerating objects?
For a deceleration in 7 seconds which area do we use?
Do we use the area for the triangle or do we include even the area under the triangle which makes it area of a trapezium?
- 213k
1
vote
3
answers
596
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Is the derivative of the magnitude of a position vector the speed? Is the integral of the speed the magnitude of a position vector?
I'm reading a book titled "Introduction to Mechanics" by Kleppner, and I came across an example: A bead moves along the spoke of a wheel at constant speed $u$ meters per second. The wheel ...
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-1
votes
3
answers
112
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Would the acceleration of a model rocket be constant for a constant thrust or not?
The question is this:
I believe the answer is A as the gravitational field strength becomes lower for larger distances of the object from the earth, but the model answer as as below:
Are they ...
- 1,238
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votes
2
answers
48
views
Calculate the space traveled by a mobile [closed]
Calculate the distance that the mobile traveled,if the initial velocity is 5m/s (meters per seconds ) ,the acceleration is constant and it's 2m/s^2(meters per (seconds)^2) ,and the time it's 1 hour.
...
- 3
1
vote
2
answers
62
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Why is it that we can consider the trajectory of an object in both directions and still get the correct answer? [closed]
Sorry for the unclear title. Here is the question:
why is it that we can "reverse the motion" as if the ball was being shot from the left and up towards the roof at the angle $\theta$? Is ...
- 60.5k