All Questions
Tagged with relative-motion kinematics
171
questions
0
votes
1
answer
35
views
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
votes
2
answers
116
views
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
vote
0
answers
43
views
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
answer
76
views
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
0
votes
1
answer
44
views
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 ...
- 159
-2
votes
1
answer
61
views
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
vote
1
answer
77
views
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
0
votes
1
answer
53
views
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 ...
0
votes
0
answers
51
views
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
votes
2
answers
430
views
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
0
votes
1
answer
121
views
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 ...
0
votes
5
answers
1k
views
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
vote
1
answer
60
views
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
0
votes
1
answer
44
views
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 ...
- 324
-2
votes
1
answer
60
views
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?
- 105
4
votes
5
answers
711
views
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
0
votes
0
answers
41
views
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
votes
1
answer
282
views
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
5
votes
5
answers
1k
views
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
0
votes
1
answer
48
views
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
0
votes
2
answers
153
views
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 ...
- 1
1
vote
1
answer
46
views
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 ...
- 171
5
votes
3
answers
2k
views
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 ...
- 59
3
votes
3
answers
515
views
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
0
votes
3
answers
239
views
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
0
votes
2
answers
74
views
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=+...
- 41
4
votes
3
answers
1k
views
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 ...
- 143
0
votes
1
answer
95
views
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 $30^\circ$...
0
votes
1
answer
76
views
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 ...
- 169
9
votes
3
answers
2k
views
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