All Questions
143 questions
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3
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Is retardation reported with opposite sign as that of acceleration?
Does retardation have opposite sign of acceleration? For example if acceleration of a car is 15m/s² than if we are asked to report retardation will we report it as -15m/s² or simply there is a ...
- 69
2
votes
2
answers
193
views
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?"
...
-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 ...
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_{...
- 21
-2
votes
1
answer
89
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Can we relate newton's second law and kinematics equations? [closed]
Specifically,
If vi = 0, then
a = vf^2 / 2s [ s = distance travelled]
And from newton's 2nd law,
a = Fnet / m [ m = mass of object]
But I've tried to them on a bunch of different problems, and they'...
- 811
3
votes
5
answers
197
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What happens physically when object is thrown up when $v$ becomes 0 at max height?
When velocity=0 during maximum height when an object is thrown up, what does that actually mean?? does that actually mean that the object doesn't change it's position over dt time period when at ...
- 31
0
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1
answer
94
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Velocity and acceleration of a ball shot uphill [closed]
Consider a ramp of length $100$ m and with a height of $10$ m. At the base of that ramp we're shooting a ball of mass $12$ kg uphill. Let's say the ball has a speed of $1$ m/s at $1$ m uphill. How can ...
- 103
-2
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1
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101
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What is $V$ in $a$=$V$$dv$/$dx$? [duplicate]
$a$=instantaneous acceleration
$V$=instantaneous velocity
$x$=position
$dx$=small Chang in position
$a$=$dv$/$dt$
multiplying numerator and denominator by $dx$,we get
$a$=$dv$.$dx$/$dx$.$dt$
now we ...
- 161
0
votes
1
answer
183
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If centripetal acceleration is pointed radially inward and it has a value $Ac = v^2/r$ is there not a value for centripetal velocity?
In uniform circular motion, an object is said to move tangentially along a circular path with a changing tangential velocity but a constant tangential speed. The velocity changes because the direction ...
- 41
2
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4
answers
166
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How can I factor friction into acceleration, given power?
I'm trying to work out an acceleration curve for a vehicle for a simulation, but despite a bunch of research there are a couple of things I still don't understand.
First we have $P = mav$. Assuming ...
- 157
1
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6
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113
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If a body moves along a path (any path, not just circular) with constant speed, is it's tangential acceleration necessarily zero?
If a body moves along a path (any path, not just circular) with constant speed, is it's tangential acceleration necessarily zero?
I could only find general proofs for the case of circular motion and ...
-1
votes
2
answers
74
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If a ball experiences a force when it hits the ground, why can we still use the kinematic equations to solve for its freefall time?
Suppose a question states:
A ball is dropped from a height of 2m. Find the time it takes for which the ball is in free fall.
To solve this, we would plug in our known values into the kinematic ...
- 105
6
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4
answers
838
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How can I write the vector form of this equation, $a = vdv/dx$?
My Physics teacher was deriving the 'Work-Energy Theorem' for a single particle in the class; where after doing the vector addition of all the forces acting on the particle, he put the resultant of ...
- 65
1
vote
1
answer
64
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Speedometer Dilemma [closed]
This is what is written in Resnick Halliday Krane Physics Vol.1
The speedometer of a car indicates it's speed, not it's velocity, because it does not specify a direction. Speed is a scalar, since it ...
- 31
2
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1
answer
113
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What happens if I rewrite the acceleration in work formula this way?
Work is known as
\begin{equation}
W=\vec{F}.\vec{q},
\end{equation}
thus for a gravitational force $\vec{F}_g=m\vec{g}$ we have
\begin{equation}
W=mgh.
\end{equation}
My derivation is as follows:
\...
user330731
0
votes
2
answers
358
views
Circular motion equivalent in three dimensions [closed]
Are there equations or even a concept of circular motion/tangential acceleration/centripetal acceleration in three dimensions? Maybe something called "spherical acceleration"? or am I just ...
- 75
0
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2
answers
167
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Linear Acceleration, Frames of Reference and the Laws of Physics
Alice and Bob, observers in deep Galilean spacetime, have identical rocket ships. Alice is at rest relative to an inertial frame. At $t=0$ she accelerates with acceleration $a_0$ in a straight line ...
- 75
0
votes
3
answers
707
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How does negative velocity and positive acceleration exactly and vice versa slow down objects?
I am confused. How does negative velocity and positive acceleration and vice versa slow down objects? Here are my thoughts. Please let me know if I am correct.
According to Newton's first law of ...
- 137
2
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1
answer
126
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Is this expert report wrong about basic kinematics? [closed]
This question is about the application of kinematics in an expert report for Eirikson v. Breton, ABQB 2000 798 (archived), a judgement for a case where a woman was driving a car that was accelerating ...
- 183
0
votes
1
answer
57
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Why do equation of motion fail to apply in non-inertial frame even after applying pseudo force?
I considered two cars of equal mass moving towards each other with speed 30m/s and 18 m/s respectively and when they are 100 meters apart they both start de accelerating at 6m/s² each.
So if we ...
15
votes
3
answers
4k
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Why does solving the differential equation for circular motion lead to an illogical result?
In uniform circular motion, acceleration is expressed by the equation
$$a = \frac{v^2}{r}. $$
But this is a differential equation and solving it gets the result $$v = -\frac{r}{c+t}.$$
This doesn’t ...
- 153
1
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2
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86
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Is an object on a parabolic path always under constant acceleration?
We know that an object under constant acceleration follows a parabolic path (as long as the acceleration and velocity are not parallel), but is the converse also true?
What's the easiest way to prove ...
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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 (...
4
votes
3
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794
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Why is harder to accelerate object at higher speeds if speed is relative term?
Why is it harder to accelerate object at higher speeds (even if resistance forces dont exist) if speed is a relative term?
Object speed is relative term, it depends from wich frame of reference we are ...
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1
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40
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The Acceleration of a particle varies from $2m/s^2$ to $4m/s^2$ as its position changes from 40mmt o 120mm. Can I get Veloc. at 120mm if v=0.4 at 40mm [closed]
I realize this might be an absurd questions to ask directly here, but I cannot seem to wrap my head around it. There is no information about the time, and I have not studied any equations when the ...
2
votes
1
answer
39
views
Finding Average Acceleration with only given angle [closed]
A car enters a curve in the road with a speed of 32 m/s and emerges from this curve 4 s later with the same speed. However, the direction of the velocity changes by 150 degrees during this time.
What ...
- 21
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1
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31
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How much time does it take bodies to change their current state of motion?
Correct me if I’m wrong in any of this
bodies with mass tend to resist any change in their state of motion .. if they are at rest .. they resist motion and if they are in motion they resist being put ...
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7
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4k
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The direction of the velocity of a body can change when its acceleration is constant. How is it possible since acceleration is a vector quantity?
As we already know that acceleration is a vector quantity which means that it has both direction as well as magnitude. It can also change given any one of the two or both (magnitude and direction) ...
0
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3
answers
290
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How is position calculated when the acceleration is not constant?
To get the position of an object we can use the equation: $$x=x_0+v_0t+\frac{1}{2}at^2$$
But now I don't have a constant acceleration, both $x_0$ and $v_0$ start at $0$ and $v$ ends at $16 \text{ m/s}$...
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9
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3
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2k
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Is centripetal acceleration almost perpendicular to velocity or it is exactly perpendicular to velocity?
In all the derivations of centripetal acceleration that I have seen so far, the direction of acceleration is said to be perpendicular to velocity but I think it's not exactly perpendicular to velocity ...
- 463
0
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1
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192
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How can we calculate $g$ force in this maneuver?
How can we calculate $g$ force in this maneuver?
We are not dealing with conventional maneuvers like level turn or loop so what equation used to calculate g force in this maneuver?
What about other ...
- 47
4
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4
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431
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Centripetal force equation doubt
In a centrifuge, $a_c$ should be constant. If $m$ increases, the $r$ will increase in order to maintain a constant $a_c$.
Constant centrieptal acceleration is given by
$a_c={ v^2 \over r}$
and $a_c = ...
0
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1
answer
146
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Do accelerations add the same way velocities add in non-relativistic mechanics? [closed]
Can you add and subtract constant accelerations?
user310302
1
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2
answers
65
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Calculate point of rotation start for spacecraft with linear acceleration
I hope someone can help me with my problem.
I would like to move a spaceship from A to B. I want the spaceship to accelerate to the middle of the path, then rotate 180° and then decelerate.
Now the ...
- 11
1
vote
1
answer
76
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Angular vs tangential vs centripetal acceleration of a non-rotating object [closed]
I was presented with a physics problem which asks to determine the maximum angular acceleraion. Unsure of how to do this, I did some research and came across the terms angular, tangential and ...
3
votes
2
answers
320
views
Can we use relative motion if acceleration of two bodies are different?
Suppose, on the $x$-axis, a body $A$ is moving with velocity $v_1$ and acceleration $a_1$, and a second body $B$ is moving with velocity $v_2$ and acceleration $a_2$. $B$ is at a distance of $S$ from $...
0
votes
4
answers
392
views
Are there two normal forces here?
In this question the normal force direction on the collar was determined to the left, while there is a possibility to be to the right direction also since the collar contacts the rod in both ...
1
vote
5
answers
227
views
Acceleration vector at an extremum
A skier moves along a ski-jump ramp. The ramp is straight from point A to point C and curved from point C onward. The skier speeds up as she moves downhill from point A to point E, where her speed is ...
- 169
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5
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5k
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Why is the acceleration along $x$-axis during projectile motion equal to 0?
Why is the acceleration along x axis during projectile motion equal to $0$?
And if it is equal to $0$ then the object shouldn't stop along x-axis after vertical velocity reaches $0$ along $y$-axis.
- 15
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1
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52
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Motion of rocket in flat space
Assume a rocket in hypothetical flat space which is at rest with thrusters off.
The role of thrusters is to help the rocket accelerate.
If the rocket has to move with uniform velocity it will first ...
- 159
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4
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295
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What happens when a body is moving in a non-uniform circular motion?
What happens when a body is moving in a non-uniform circular motion where tangential acceleration is also present?
Will it continue to move in circular path or it will take an elliptical orbit?
user297948
1
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1
answer
218
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Acceleration vector at an acute angle to velocity vector
What will be the description of motion of particle if acceleration vector always make an acute angle with velocity vector?
I know that if acceleration vector makes right angle with velocity vector ...
- 892
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1
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116
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Regarding Uniform Acceleration [closed]
Please give some basic intuition or hint to solve this question. I'm getting stuck.
The star of a distant solar system explodes as a supernova. At the moment of the explosion, a
resting exploration ...
- 1
3
votes
2
answers
105
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Which is the centripetal term here?
In spherical coordinates the acceleration can be written as
$$\textbf{a} = \dot{\textbf{v}} = \ddot{r} \hat{\textbf{r}} + \dot{r} ( \dot{θ} \boldsymbol{\hat{\theta}} + \sin θ \dot{\phi} \boldsymbol{\...
- 1,340
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1
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34
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Solving an infinitely decaying propelling system [closed]
I am a HK secondary school student who is taking part in the HKPhO training in my school. I was doing some training questions and struggled with this question:
A car with initial speed $v_0$ is ...
4
votes
2
answers
2k
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Why the formula of kinetic energy assumes that the object has started from an initial velocity of zero?
According to my physics textbook, the formula of kinetic energy is:
$$
W = \frac{1}{2}mv^2
$$
Where $m$ is is mass of the object and $v$ is the velocity of the object. The equation is calculated from ...
3
votes
1
answer
1k
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Confusion in coordinate transformation of acceleration vector
Consider this notation for vectors:
$A_{cb}^{d}$ is the $A$ vector (velocity,acceleration, angular velocity or ...) of $b$ coordinate frame w.r.t. $c$ frame presented in $d$ frame axis.
I know when we ...
- 31
5
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5
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749
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In circular motion, is the trajectory a resultant path of the given velocity and the velocity due to the centripetal acceleration?
For circular motion to happen we need a centripetal force or acceleration i.e. a force perpendicular to the direction of motion at all instants. So without any perpendicular component of force ...
- 8,476
0
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3
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1k
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What is the difference between non-uniform velocity and acceleration?
So I know non-uniform velocity as, "Non-uniform velocity is when an object covers unequal distance in equal interval of time in a particular direction or covers equal distance in equal interval ...
- 1
2
votes
3
answers
253
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How do we define $G$s?
I am going to explain what I think I know and how that leads up to my question - please correct any false claims I make or conclusions I draw.
I initially thought that $G$s were defined purely by ...
- 318