All Questions
Tagged with relative-motion kinematics
171
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How to calculate the relative speed when three bodies are involved? [closed]
Two trains A and B start from a station and move in parallel tracks with velocities 40 kmph and 60 kmph respectively. A man sitting in train A. watches a lady who walks inside the train B at a speed ...
-1
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2
answers
116
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How Fast Must a Man Run to See Rain Falling horizontally?
The fact that tan 90° is undefined indicates a key issue in the problem.
Does this mean it is impossible to observe rain falling at 90 degree?
When rain is observed to be falling at 90° with the y-...
1
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0
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43
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The stupidest question ever on relative kinematics and angular velocity [duplicate]
I am scratching my head on a very basic formula whose meaning escapes my intuition.
On basically all texts of mechanics the following result is derived:
Suppose that a rigid body is moving with ...
- 130
1
vote
1
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76
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How does relative motion work for an extended object?
I have this conceptual doubt which might be flawed very badly but I don't understand this particular thing. For example, if one end of a stick is moving with velocity $v_1$ and the other with $v_2$, ...
- 123
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1
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44
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The locus of the velocity vectors of a boat navigating in the sea under the presence of a very strong wind?
I already asked a question very similar to this one here and I think the solution would not work when the boat navigates in the sea when a very strong wind blows. That is I am trying to find the ...
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1
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61
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The distance problem [closed]
Say a car has to move from Point A to Point B on the surface of the earth. The car starts from rest at Point A at time $t=0s$ reaches point B at time $t=10s$ with a constant velocity of $1000 m/s$. ...
- 87
1
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1
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77
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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 ...
- 27
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1
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53
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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 ...
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51
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Why is throwing a bullet by hands not effective as using a gun? [duplicate]
The bullet when fired applies equal and opposite force to the Gun, (Newton's 3rd law)
Thus to keep the gun stable we apply some force which should be equal to the force applied by the bullet.
If we ...
2
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2
answers
430
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Is all change movement? [closed]
Is there a change in the universe that cannot be reduced to movement? One counter-example should be enough. :)
Heat is a type of change that was once thought to be qualitative, but is now realized to ...
- 137
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121
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Velocity of Separation and Relative Velocity
I have some problems in understanding a concept, which has been used in the problem in the picture:
I don't understand what are we actually using to solve this question. Are we using relative ...
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5
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Do released objects take the direction and speed of their parent frame's velocity, or just the parent frame's speed component?
Context: I'm working on a space game. I noticed that an unpowered object fired from a strafing spaceship appeared, as the released object moved, to curve in the direction the ship was strafing. This ...
1
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1
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60
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Simple classical mechanics problem to compute minimum distance attained between two ships moving with constant velocity
I have been reading the book "A Course in Classical Physics 1 - Mechanics" by Alessandro Bettini. I have reached a problem in the first chapter that I am having trouble with.
The problem ...
- 121
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1
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44
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Is the relative velocity between these two particles increasing or decreasing? [closed]
The displacement time equations of two particles are:
$$s_1 = 2t-4t^2$$
$$s_2 = -2t + 4t^2$$
By differentiating we can find $v_1,v_2$. Subtracting them gives: $v_1-v_2 = 4-16t$
Clearly, this ...
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1
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60
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What is the relative acceleration of a ball thrown inside a bus with respect to a man sitting inside if bus has uniform velocity? [closed]
Like both man and ball are experiencing acceleration due to gravity so will the ball have no acceleration w.r.t to man?
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5
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711
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Can't understand a statement about motion
From the book where I am studying motion, It says
Motion is a combined property of the object under study and the observer. There is no meaning of rest or motion without the viewer.
I know that, for ...
- 157
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41
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Minimum seperation of moving objects doubt
Let there be $2$ objects $P_1$(initial velocity $u$ $ms^{-1}$ & acceleration $a$ $ms^{-2}$) & $P_2$ (initial velocity $U$ $ms^{-1}$ & acceleration $A$ $ms^{-2}$) initially separated by ...
0
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1
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282
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Angular velocity of a particle in uniform circular motion about a general point
This problem was given by our professor.
Consider a particle P executing uniform circular motion wrt the point O with uniform angular velocity $\omega$ anticlockwise whose cordinate is $(2R,0)$ in a ...
- 74
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5
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1k
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How is a change in KE the same in every inertial reference frame?
This is not about special relativity, so assume speeds are much less than $c$.
This article says a change in kinetic energy (KE) remains constant in all inertial reference frames.
So the kinetic ...
- 410
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1
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48
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Kinetic energy consistency
Suppose a vehicle 1 is on the top of another vehicle 2 (we can think of it like a big platform).
Imagine the following independent experiments:
Suppose that the top vehicle accelerates to a speed $...
- 31
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2
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153
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Average speed / Velocity
We know that in kinematics we have the concepts about "average speed". By definition the average speed is the total of the distance divided by time, but I still don't get it what is the ...
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1
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Linearly Interpolating in a Non-Inertial Frame
I am working on an engineering task where we have a flying object which knows its height above a curved surface as well as how close it is to other flying objects. If I want to interpolate between two ...
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3
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What is the "true" distance an object travels based on relative speeds?
There are two objects (x and y) with x travelling at 10km/h and y travelling at 11km/h, both with respect to the earth. After 1h, from the perspective of the earth, y travels 11km, but from the ...
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3
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3
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515
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Relative velocity related to acceleration
Let's say we have a car moving on the horizontal ground with a velocity of $10 \hat{i} \frac{m}{s}$. A person inside throws a ball vertically upward with a velocity of $3 \hat{j} \frac{m}{s}$. Now I ...
- 169
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3
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239
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A question about relative motion and how to make sense of it
So, here is the question:
Assuming the 2D Cartesian system and the basis vectors $\hat{i}$ and $\hat{j}$, we have two cars A and B located at (0,6) and (-30,0) respectively. Car A starts moving with a ...
- 169
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2
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74
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Sign convention for relative displacment
If an object A is $X\ \mathrm m$ behind B,than the relative displacemnt of A wrt B would be $-X$. However is object A was moving towards B(at rest) at a rate of $Y\ \mathrm{m/s}$, then $$V_{ab}=+Y-0=+...
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3
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Kinetic energy "paradox" -- where am I wrong here? [duplicate]
Body $A$ is at rest and has mass $2$, so the energy required in order to accelerate it to a speed of $v$ is $v^2$, and so the energy required in order to accelerate it to a speed of $2$ is $4$.
On the ...
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For an airplane moving north from some latitude (say $30^{\circ}N$), why does rotation of the Earth cause an increase in apparent drag?
I'm not able to understand the answer to this example:
Example 10 from the Curtis Orbital Mechanics text book :
An airplane of mass $70 000\ \mathrm{ kg}$ is traveling due north at latitude $30^\circ$...
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1
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76
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How do you find relative motion of two objects not travelling in a straight path?
I understand relative motion linearly, but how about more complex motion, like travelling in a circle? Would you just find the objects velocities at some point using the formula $v=\omega r$ and then ...
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3
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2k
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Greatest distance between a particle moving with constant velocity and a particle moving with constant acceleration
Two particles start moving along the same straight line starting at the same moment from the same point in the same direction. The first moves with constant velocity $u$ and the second with constant ...
- 309
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2
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133
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How do we know if a particle is moving or not? [duplicate]
if there is only one particle in the universe, how do we know if it is moving or not?
We don't have any other object to track the distance between the two, then is it possible to determine the ...
- 103
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1
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111
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Distance between two airplanes [closed]
I need help with a vector problem where my solution is different from that of my teacher. The translation of the problem reads as follows:
An air traffic controller observes two aircraft on his radar ...
4
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1
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151
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Relative Circular Motion [duplicate]
Four particles $P_1, P_2,P_3,P_4$ are moving in a plane. At $t=0$, they are at the four corners of a square $ABCD$ of edge length $l$. Each of the particles has a constant speed $v$. The velocity of $...
- 345
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107
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CoM-and-relative velocity
In our scrip we are considering the elastic collision between two particles, one with inital velocity $\vec v$ and the other $\vec w$. We also consider that the particles have the same mass.
...
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2
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278
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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 $...
3
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2
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67
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Relative Velocity (Kinematics) [closed]
I was studying the concept of relative velocity and after solving a few problems I am running into this confusion.
a) Let’s say two cars are moving perpendicular to each other (no collision) with ...
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3
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675
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I am moving right and rain is falling vertically down.Why should I hold umbrella at an angle?
This is related to relative velocity.I get that, from my moving frame of reference rain is making an angle.But still... it doesn't make sense to hold umbrella at an angle when rain is falling ...
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1
answer
124
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Velocity of an object with respect to the same object
I know that velocity of an object with respect to the same object is a null vector but I'm not able to get a grasp of it.
Whatever I had thought till now is that if I'm sitting in a train (which may ...
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2
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7k
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What will be the minimum drift possible when a boat crosses a river? [closed]
Imagine a boat with a constant speed $v$ that has to cross a river of width $d$. Let the river flow with a constant velocity $u$. I want to know the angle at which the boat should sail in order to ...
0
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1
answer
35
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Using rate and per unit time together for describing effects of motion
I have observed recently 3 different elementary definitions of velocity
Rate of change of position, change in position per unit time ,and
rate of change in position with respect to time,so I am not ...
1
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2
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428
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Apparent wavelength received by observer in doppler's effect
I have a few doubts about Doppler's effect.
Does the apparent wavelength received by the observer depend upon whether the observer is moving or not?
$λ_{apparent}=\ \frac{v_{sound}\pm v_{source}}{f}$....
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On a rainy day, a man is running on a hilly terrain in such a way that he is always finding the rain drops hitting him vertically
It is assumed that rainfall is uniform in the whole terrain from O to E(figure attached) When the man was at rest on stretch OA, he found the rainfall at an angle of $30^o $ with the vertical.
What ...
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1
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278
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Relative position from two reference frames
Here, clearly $\vec{r}_{S'S} + \vec{r}_{PS'}= \vec{r}_{PS}$. Then we differentiate and double differentiate and get the standard equations of relative velocity and acceleration.
Now according to my ...
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1
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Why do we say the resultant vector as the relative motion in this case?
If a car A moves with acceleration $2m/s^2 $due east and car B moves $1m/s^2 $due north. What would be the acceleration of car B with respect to car A. Now , for this. The solution in my textbook is ...
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2
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131
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Can I apply Newton's equations of motion to relative motion?
We know that
Velocity of A relative to B is
$$ \vec v_{A|B} = \vec v_A - \vec v_B $$
and Acceleration of A relative to B is
$$ \vec a_{A|B} = \vec a_A - \vec a_B $$
So, is it correct to do this to ...
- 227
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3
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133
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Question regarding relative velocity of muzzle bullet? [closed]
A police jeep is chasing with, velocity of 45 km/h a thief in another jeep moving with velocity 153 km/h. Police fires a bullet with muzzle velocity of 180 m/s. The velocity it will strike the car of ...
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Why is direction of train like this for car?
This is an image of a train and a car. T is the train moving towards - $x$ axis and C is the car moving towards $+ y$axis.
So, my teacher made a resultant velocity with $-5\hat i$ and $-20\hat j$. ...
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2
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40
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Is this correct regarding velocity of train?
So many yellow T drawn are just different position of train at different instants.The person is standing still at all those instants at one place.
If a train is moving at 5m/s.
Then for me , can we ...
- 725
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1
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38
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Direction of $V_RM$ confusion
So ,please read both the questions . They have similar originate questions that I am facing difficult in.
Let us say rain is falling downwards with v = -5j and a man is moving with a velocity of 2i in ...
- 725
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0
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59
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Discretizing kinematics of moving object
I think this is a simple question, but I'm unable to find the relationship:
The relative distance between two objects at any time $t$ can be written as:
$x_r(t)=x_{ro}+\int_{t_0}^{t_f}v_r(t)dt$
where:
...
