The tag has no wiki summary.

learn more… | top users | synonyms

-4
votes
0answers
30 views

Relative motion problem [on hold]

A fighter plane flies at a velocity of 300 m/sec. On the fighter plane there is a gun which shoots at a rate of 40 rounds per second with a muzzle velocity of 1200m/sec. The shots are aimed at another ...
-1
votes
3answers
115 views

Isn't a physical frame of reference useless for calculating speed?

Please ignore relativistic effects and the effects of the expansion of space-time due to the expanding universe theory for the purposes of this question. Whenever someone asks what is the speed of X, ...
2
votes
0answers
36 views

Would impact angle matter on relativistic impactor?

I'm trying to calculate (for fun) a comparison between a kinetic impactor and an H-bomb. I would assume this to be a fairly straight forward problem involving kinetic energy and a table of various ...
9
votes
3answers
1k views

Do you encounter more photons (per unit time) when moving forwards at a constant velocity?

Let's say you have rain hitting you evenly on all sides (not very realistic, I know). If you were to move forwards at a constant speed, there would be more droplets of rain hitting you per second on ...
0
votes
1answer
34 views

Relative motion with two observers

For four particles A, B, C, D , the velocities of one with respect to other are given as $ V_{DC}$ (Velocity of D with respect to A) is 20 m per second towards north, $ V_{BC}$ is 20 m per second ...
70
votes
11answers
11k views

If all motion is relative, how does light have a finite speed?

I've often heard that Einstein shattered the notion of absolute motion (i.e. all things move relative to one another) and that he established the speed of light as being absolute. That sounds ...
1
vote
3answers
44 views

Unable to understand relative motion

If you sit in a fast moving car on a highway, you will see the objects outside the window moving backwards with respect to you. Assume that your motion is uniform. One would think that all static ...
14
votes
5answers
1k views

Can we find actual rest mass of things on Earth

Earth moves around the Sun and the Sun moves around the galaxy and the galaxy moves with unknown speed and direction. We have speed so the mass of us all altered. Can we know the real rest mass? If ...
0
votes
2answers
118 views

How insects got hits on the wind shield of a car?

There are rare chances when any insects got hit the wind shield of a car while driving in highway but it makes to wonder that how is that happen ? Does insect suffered a greater change in momentum ...
1
vote
1answer
41 views

Smooth collar sliding down smooth shaft [closed]

For part (a), we find that the acceleration of the collar is $6.94~\mathrm{m/s^2}$. In part (b), we say that the acceleration of B with respect to A is $6.94~\mathrm{m/s^2}$, which makes sense. ...
2
votes
1answer
46 views

Relative Velocity Help

I am struggling with relative velocity and so decided to do some extra problems in my textbook. I have 2 problems that seem to contradict, and its annoying things like this that throws me off, leaving ...
1
vote
1answer
100 views

Trajectory of a swimmer trying to reach the opposite bank [closed]

I came across the following question 2 days ago: $Q$. A swimmer is swimming in a river with a speed $u$ with respect to the speed of water which is $v$. It is assumed that the river has straight ...
3
votes
1answer
101 views

Is this one of the reason we can't travel in time? [closed]

I'd like to ask a question that is not in my field but it's bothering me. Based on that, I'm sorry if I make dumb mistake in my assumptions. The idea of travelling in time means "going" at some ...
0
votes
1answer
27 views

Relative Velocities/Accelerations

I seem to just not understand how relative velocities and accelerations work. Here is a problem that I will use to ask my question: When the box lands, its moving 3m/s to the right, and the belt ...
1
vote
1answer
45 views

Coriolis Effect vs airplane

So, if I build a highway from north pole towards equator and sit in a car, speed pretty fast towards it, I should feel force with the Earths rotation due to the different rotation speeds of this ...
3
votes
2answers
1k views

How does a spacecraft enter Earth's atmosphere?

If Earth whirls around the center of our galaxy at some 220 kilometers per second, how can a spacecraft, which is much slower, enter Earth's atmosphere when returning from Mars for example?
1
vote
1answer
32 views

Relative Movements Agreement on Object speed

I am confused about Relative Motion.Lets suppose we have one train and two observer.One of them inside the train and the other one is outside.Lets think the outside observer see the train moves a ...
0
votes
2answers
88 views

When we are inside a plane and look outside the window why does everything (outside) appear to be at rest?

When we are inside a train and we look outside the roadside trees appear to be moving in the opposite direction but when we are inside a plane and look outside the window everything seems to be at ...
0
votes
0answers
24 views

Relative speed and time [duplicate]

There is a notion that travelling at the speed of light is impossible for a matter. But what if the there are 2 objects that are coming towards each other with half the speed of light. Thus relatively ...
0
votes
0answers
39 views

Is it possible to derive the Doppler effect formulas for sound using relative velocity?

Is it possible to derive the Doppler effect formulas for sound using relative velocity? If possible can anyone please explain it to me.
1
vote
1answer
91 views

Since the Earth is moving through space, do we experience time dilation?

What I mean is, the Earth orbits around the sun at around 30km/s, while I understand that this isn't a very high velocity does time dilation still occur to say a person who is completely stationary in ...
0
votes
1answer
65 views

Does it take more effort to move against earth's rotation?

I know that if we stand still, we are traveling at 0 m/s relative to the Earth. But if we move against the rotation of the Earth we lower our speed, so, wouldn't we have to fight against the ...
0
votes
1answer
98 views

Since Earth spins, would an aircraft travelling opposite to direction of Earth spin take less time? [duplicate]

Suppose we want to reach the point on earth which in relative terms is exactly on the opposite end of the sphere we call earth (I know it is not an exact sphere). We either dig vertically downwards, ...
-2
votes
1answer
89 views

Earth's direction in space [closed]

After watching videos about the rotation of the planets being helical and not heliocentric, I wondered, as Earth travels through space, which part of Earth is the forefront?
0
votes
1answer
26 views

Why distant are stationary?

Why do for an observer looking out of the window through a fast moving train ,the distant objects appear to be stationary?
-1
votes
1answer
48 views

Simultaneous observations in relativity

Consider an object which responds to two different signals A and B: it responds to signal A with blue color and signal B with red color. Also, it responds only to the signal that reached first. In ...
3
votes
4answers
916 views

Puzzling : Relative motion of two points on a rotating disc

Consider two points on a radial line for a rotating disc. One point, $A$, is at the circumference and the other, $B$, is at distance $R/2$ from disc's centre. Relative velocity of $B$ w.r.t. $A$ ...
0
votes
1answer
26 views

Who is moving and with who's relation?

What if we are in a cube of 3×3 m  which is further enclosed in a sphere of radius 50 m? And the sphere start to rotate on its own axis would we experience force? If not then what happens if there is ...
0
votes
0answers
28 views

Faster than light travel at half speed [duplicate]

Peter and Susan are facing each other in outer space. Both of them ignite their their incredibly powerful jet pack thrusters and accelerated away from each other to just over half the speed of light. ...
1
vote
1answer
44 views

Speed of a river [closed]

I've got a problem (Sorry if it's too basic). It is: Going upstream in a canoe, the passengers throw an empty bottle. They keep rowing for 60 minutes, and move 2 kilometers upstream. They then start ...
3
votes
2answers
128 views

Kinetics energy with different reference frame (a fighter plane shoots a bullet)?

Let say a plane flights at 1km/s, shoots a 2kg projectile at 1km/s, so to the Earth, the projectile flights at 2km/s with 2*2*2/2 = 4MJ. The same gun when fixed on Earth, shoots the same 2kg ...
-1
votes
1answer
96 views

Problem related in relative motion [closed]

The speed of a boat is 1.5 m/s in still water. One needs to cross a river of width 500 m with this boat. Along the direction of the river a strong wind is blowing with a speed of 0.9 m/s. The boat is ...
1
vote
1answer
175 views

Problem on relative motion involving wind speed .Finding the real velocity of wind?

Here is the question For a person running west at 7km/hr wind appears to blow from north-west .But when he walks towards west at 3km/hr the wind appears to blow from the north. What is the true ...
0
votes
1answer
46 views

Muzzle Velocity confusion

Does muzzle velocity refer to the velocity of the bullet with respect to ground or the velocity with respect to the gun?
0
votes
1answer
376 views

Apparent frequency and wavelength in the Doppler effect

For a transverse wave(or for pressure waves required to produce longitudinal waves), the motion perpendicular to the direction of propagation of the wave is governed by an equation like $y = ...
0
votes
2answers
117 views

Why do objects seem to move faster (relatively) when they move tangential to the observer?

I've observed this loads of times while travelling, in cars, trains,etc.I can't quite put it in words and therefore I've roughly made a diagram to assist my question. Assume an observer is travelling ...
1
vote
1answer
58 views

Space and motion

When we throw a ball upwards sitting in a running bus or train it directly comes to our hands but when we do the same sitting on a moving motorcycle the ball falls backwards. Why?
0
votes
1answer
67 views

Relative Motion of Child and Boat [closed]

A boat is traveling upstream at $11~\text{km/h}$ with respect to the water of a river. The water is flowing at $7.0~\text{km/h}$ with respect to the ground. What are the (a) magnitude (b) ...
0
votes
2answers
83 views

What logic did Newton give in support of using relative spatial measurements? [closed]

The crux of space-time is that it is one thing to have abstract concepts of absolute space & time,and it is other thing to describe the actual motion of an object in terms of measured changes of ...
0
votes
1answer
130 views

Solving relative velocity without Lorentz transform [closed]

A train with proper length $L$ moves at speed $\frac{5c}{13}$ with respect to the ground. A ball is thrown from the back of the train to the front. The speed of the ball with respect to the ...
1
vote
0answers
39 views

Wind resistance on moving body

Suppose that a vehicle is traveling 60 km/h north, and the wind speed is also 60 km/h going the same direction, would there be wind resistance, and to what extent? Also, if I put my hand outside the ...
1
vote
1answer
87 views

How fast am I moving? [duplicate]

Given the speed of light is 299,792,458 meters per second and that it is constant through out the universe, (i.e a person who measures the speed of light while standing still will get the same result ...
33
votes
3answers
2k views

What are galactic speeds measured against?

The Earth moves through space at 67,000 MPH. The Milky Way travels through a local group at 2,237,000 MPH. Wouldn't you need a fixed point to be able to measure velocity against? After all, compared ...
0
votes
0answers
36 views

Does a body curve spacetime at higher velocities? [duplicate]

Suppose we have two objects where the distance over time decreases. Now, as I understand it, general relativity says that we can observe the Universe from the perspective of both objects an get a ...
-1
votes
1answer
113 views

When you are standing in a running train if you jump means will you be in same place or will you be in front or back? [duplicate]

When you are standing in a running train if you jump means will you be in same place or will you be in front or back?
2
votes
0answers
41 views

2d particle collision, Time for one particle to catch another one [duplicate]

Say we have 2 particles where 1 moves with constant velocity $u$ and the other moves with speed $v$ towards the first particle. After what time does the 2nd particle catches up with the 1st one?
18
votes
3answers
5k views

Why doesn't the speed of Earth (moving through space) kill us?

I have read different speeds of Earth in different sources. $382\;{\rm km}/{\rm s}$, $12\;{\rm m}/{\rm s}$ and even $108,000\;{\rm km}/{\rm h}$. Basically, it's moving too fast around the Sun. And the ...
1
vote
2answers
199 views

Magnetic force as a relativistic effect?

There is something I am confused about when it comes to the force between two parallel wires carrying current, specifically why when they carry current in the same direction the wires are always ...
1
vote
6answers
3k views

The earth is spinning, so why don't we jump and land on a different location?

I know there are similar questions in stackexchange but i think it's different and detailed. The earth is spinning 465 meters/second so why don't we jump and land on a different location ? I have ...
2
votes
3answers
281 views

The effect of windspeed on a car

I've worked problems in the past in trig class concerning the effect of wind on the speed of a plane and it's flight path and was wondering if a similar thing occurs with a car. First off, I'm ...