All Questions
Tagged with relative-motion newtonian-mechanics
200
questions
1
vote
1
answer
57
views
Confusion about sign conventions used in the Doppler formula
Wikipedia gives the Doppler formula as:
$ f = \left( \frac{c \pm v_r}{c \pm v_s} \right) f_0 $
c is the propagation speed of waves in the medium.
$v_r$ is the
speed of the receiver relative to the ...
- 6,112
1
vote
0
answers
70
views
Does relative velocity apply before or after the impulse?
I'm solving the following question from Kleppner and Kolenkow:
My solution differs from the textbook solution not only in the magnitudes in parts (a) and (b) but also the conclusion in part (c). ...
- 1,581
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
0
votes
3
answers
84
views
Conceptual meaning of frame of reference for kinetic energy
what does the statement
The speed, and thus the kinetic energy of a single object is frame-dependent (relative)
even mean? does the impact of a collision of moving bodies and henceforth transfer of ...
0
votes
2
answers
74
views
Accelerating body in a non-inertial frame of reference
If a body is subjected to a force, can I find a non-inertial frame of reference in which the body is not accelerating?
- 21
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 ...
1
vote
1
answer
75
views
Principle of Relativity and the invariance of Newton's law in IRFs
Newton's law are form invariant under the coordinate substitutions:
$$
\tilde{x^{i}}=x^{i}+a^{i}
$$
This means that Newtons' equation of motion,
$$
F^{i}=m \frac{d^{2} x^{i}}{d t^{2}}
$$
(where $i=1,2,...
- 11
0
votes
2
answers
76
views
In galilean relativity, is an observer assumed to be at rest only to simplify calculations, or is there a physical reason for this assumption?
I am a beginner in Physics and my teacher taught us "Relative Motion" yesterday. He said that the "Observer is assumed at rest." Is the observer assumed to be at rest only to ...
5
votes
2
answers
850
views
Does kinetic energy rely on the observer mass too since velocity is relative?
There is no 'correct' inertial reference frame according to relativity. Objects are only 'in motion' relative to an arbitrary inertial reference frame. So let us take the following example. A person ...
- 1,009
2
votes
1
answer
110
views
Flying mosquito problem [duplicate]
Let's say there is a car and its doors and windows are closed. Basically it is a closed space inside. There is a mosquito hovering right in the center of closed space of the car. While doing so the ...
- 39
1
vote
0
answers
37
views
Is e (COR) defined for whole situation or just during collision
According to wikipedia
$${\text{Coefficient of restitution }}(e)={\frac {\left|{\text{Relative velocity after collision}}\right|}{\left|{\text{Relative velocity before collision}}\right|}}$$
...
- 379
1
vote
4
answers
94
views
A problem Understanding how a two-body system of planets starts rotating around barycentre
Consider,We are Creating a Two-body system in free space,Where no other mass exists,Let's Take First Mass M1 and hold it,Now bring Second Mass M2,hold it up,Now we are giving a suddenly impulse To M1 ...
- 452
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
7
votes
6
answers
2k
views
Is it wrong to just say that things continue at constant velocity unless acted upon, as velocity is only relative?
Like when saying that people mistakenly thought things automatically slowed down after being thrown etc (accelerated), because that's just due to all the air or surface friction or gravity. Do you ...
user326693
1
vote
3
answers
9k
views
What exactly will happen if you jump in the upward direction from a roof of on a moving car?
I'm not a physicist and I'm a little bit puzzled with the image below:
I know it's a joke but if we assume we don't have air resistance what exactly will happen if someone jump in the upward ...
- 13
0
votes
2
answers
88
views
Question about relative motion from "A Brief History of Time" [closed]
I read this example in Stephen Hawking's A Brief History of Time:
If one sets aside for a moment the rotation of the Earth and its orbit round the Sun, one could say that the Earth was at rest and ...
- 1
2
votes
2
answers
129
views
Confusion regarding Inelastic Collisions contradicting my book
Suppose two bodies $A$ and $B$ with equal mass are kept at a distance. $A$ starts moving towards $B$ at a constant velocity, they hit, and I assume that it is a PERFECTLY INELASTIC collision here.
...
- 1,168
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
2
votes
5
answers
123
views
If motion relative to a frame of reference is purely relative, how do we account for the work done to move relative to the frame of reference?
I get the idea that everything is in motion, and there's no absolute reference frame for everything.
But when we consider local events, like a train passing through a town, I have trouble accepting ...
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
2
votes
0
answers
55
views
Should the velocity increase or decrease?
Suppose some projectile is traveling along the positive $x$ direction at a velocity $v$. While moving it is emitting particles, and thus losing mass. If the particles are being emitted in the same ...
- 1,791
0
votes
0
answers
76
views
Doubt regarding derivation of rocket equation
I'm having quite some issues deriving the ideal rocket equation, and I suspect it is due to lack of identifying scalar terms and vector terms. Here is how I derive it :
Let $v$ be the velocity of the ...
- 1,791
6
votes
3
answers
516
views
Interesting answer as a range of tension in pulley-block-plane system
I want some intuitive understanding on why there will be a range in tension in the below question. (On solving we will get that the system is at rest ($a=0$) and since its starts from rest the blocks ...
- 95
0
votes
1
answer
557
views
Calculating the velocity of a tennis ball after impacting a moving racket
Suppose I have a tennis ball moving with $v_1$ (blue arrow in first image below) impacting a moving tennis racket with velocity $v_r$ (black arrow in first image below)
In order to calculate the ...
- 103
1
vote
2
answers
46
views
Power Demand for Motion of Vehicle on a Road and Plain in Air with Air Resistance
Let's say we have an ideal motorcycle without frictional losses (no tire slip, ideal machine without losses). But we want to consider wind force which is proportional to the square of speed
$F = k \...
- 1,299
1
vote
0
answers
114
views
Work done on a moving cart in wind
Let us suppose a cart is moving in a rough ground with a propeller attached to the roof of the cart.
Let the velocity of the cart at the given point of analysis be V and velocity of wind is -W. The ...
3
votes
2
answers
279
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 $...
3
votes
2
answers
67
views
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 ...
- 31
2
votes
3
answers
675
views
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 ...
5
votes
5
answers
1k
views
How should I understand the idea of relativity of space?
In the book General Physics by L.D.Landau, he mentioned the following in the first and second paragraph
The fundamental concept of mechanics is that of motion of a body with
respect to other bodies. ...
- 138
0
votes
3
answers
118
views
Relative Motion and Motion on ground
When I walk on the ground I know that it's me who is walking and not that I am just moving my legs forward and backward and the ground is moving.But according to relative motion I should not be able ...
- 103
2
votes
1
answer
66
views
How would we know whether a object is moving in deep space?
In deep space, there isn't anything we can compare our position with (According to my knowledge). In other words, we won't be able to define an origin so how would we know whether we are in motion or ...
- 883
0
votes
2
answers
91
views
Why does these two masses not have same acceleration? [closed]
Assumptions: No friction , $m_2$=5kg and $z_1$=2kg. $z_2$ is fixed at its place.
Here, there is a mass of $5kg$ on a movable wedge of mass $2kg$. So, my question is that can we say that acceleration ...
- 33
1
vote
2
answers
428
views
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?
$λ_{apparent}=\ \frac{v_{sound}\pm v_{source}}{f}$....
- 292
0
votes
1
answer
41
views
Velocity Gradient and Force in Air
I have experienced that when we go on a bike at a high speed, keeping our hands close to the surface of the bike is not much a problem and we feel negligible force which the air applies on us. But as ...
- 11
2
votes
2
answers
131
views
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
-1
votes
2
answers
40
views
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
-2
votes
4
answers
490
views
Is this an exception to Newton's Second Law of Motion?
If a ball in an experiment is dropped from two different heights, 6 feet and 12 feet, why would we need to exert more force when we catch the ball that is dropped from the height of 12 feet? According ...
user282164
0
votes
2
answers
296
views
Why is relative motion at constant velocity the same as being at rest?
If I am a passenger who plays catching-the-ball game inside a vehicle that moves with a constant velocity in a straight road, why can I catch the ball repeatedly that as if the vehicle is at rest? How ...
user282164
6
votes
2
answers
680
views
How does the orbital motion of reduced mass tell us how the individual planets/stars move?
To give context to my question, here is Kepler's first Law restated in terms of reduced mass. Here, $\vec{r}$ is the position vector of the reduced mass whose origin lies at the centre of mass of the ...
- 181
0
votes
2
answers
91
views
Simple Harmonic Motion example [closed]
https://en.wikipedia.org/wiki/Escalator
https://en.wikipedia.org/wiki/Simple_harmonic_motion
Can we classify escalator device as a Simple Harmonic motion example?
- 111
0
votes
3
answers
112
views
What really pushes a rocket up?
To launch a rocket, fuel is burnt and is released in opposite direction relative to rocket and it pushes the rocket upwards because of third law of motion but the fuel molecules are not actually ...
- 171
1
vote
2
answers
547
views
Coriolis force and liquid on a rotating space station?
On a rotating wheel space station crewed by humans with sea-level conditions (temperature above the freezing point), if liquid was spilled on the floor am I correct in understanding that the Coriolis ...
- 269
1
vote
1
answer
46
views
Swing in moving truck
I was just thinking about a situation in which a big truck is moving in high speed say ( $80 \ miles/hr$). There is a swing attached with the ceiling of the truck container which can move freely in ...
- 111
-1
votes
2
answers
91
views
Velocity Question from grandparent
My Grandparent asked me this question a few years ago, and I am getting around to giving him an answer, but I don't know the answer. Can anyone help?
"A pickup truck is speeding along a highway ...
- 21
0
votes
3
answers
706
views
Coriolis effect vs preservation of angular momentum on merry-go-round, sniper's bullet, hovering helicopter and high altitude rockets
I understand that how helicopter hovers at the same position or a thrown ball falls to the same position even though earth is spinning. This is due to the preservation of angular momentum and my ...
- 101
2
votes
3
answers
150
views
Is the frame of elevator Preferred over the frame of ground? [closed]
When an object is thrown upward with some velocity then it doesn't fall towards the earth until the given velocity becomes zero.
Now imagine the case given in the figure
There is a question in my ...
- 8,230
0
votes
2
answers
84
views
How to decide which velocity is bigger in a collision before writing velocity of approach and velocity of separation?
My teacher said that velocity of separation is $V_1$- $V_2$ where $V_1$ is greater than $V_2$ and said same for velocity of approach. The problem is how would you determine which velocity is greater ...
- 5
0
votes
1
answer
312
views
Relative angular velocity of one point with respect to another on a solid rigid body [closed]
What is relative angular velocity of A wrt B and that of A wrt C in the figure given below?
Description:
A, B and C lie on a solid cylinder(rigid body) rotating with a constant angular velocity $\vec{...
- 147