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# Category Archives: AstroPhysics

## Weightlessness in a satellite

Why does an astronaut feel weightless in a space capsule orbiting the earth?

I’ve gotten a key point saying that the space capsule orbiting the earth has a centripetal acceleration, but I cannot figure out why is it related to the question.

Answer: The centripetal acceleration is provided by the force of gravity. Since the force of gravity is completely used up in providing the centripetal acceleration to the space capsule, the astronaut feel weightlessness.

## Conservation of linear momentum – Problem

Astronauts Mr.X and Mr.Y float in a zero gravity space with no relative velocity to one another. Mr. Y throws a mass of 5 kg towards X with speed 2 m/s. If Mr. X catches it, the change in velocity of X and Y are (choose the correct option)
(a) 0.21 m/s, 0.80 m/s
(b) 0.80 m/s, 0.21m/s
(c) 0.12 m/s, 0.08 m/s
(d) 0.08 m/s, 0.12 m/s

Please provide me the solution part step by step

## Question from Special Relativity

A spacecraft starts from earth moving at constant speed to planet A which is 20 light-hour away from Earth.

It takes 25 hour (according to an earth observer) for a spacecraft to reach this planet. Assuming that clocks are synchronized at the beginning of the journey, compare the time elapsed in the spacecraft frame for this one-way journey with the time elapsed as measured by an earth-based clock?

Posted by Mona

## Speed of Gravity

Why hasn’t anyone measured the speed of gravity yet?

As in, how long does it take for the gravitational field of a mass to affect another mass?

Who said that speed of gravity waves is not measured?

Please go through the links below and you ca get details,

## Parallax Method to determine the distance of stars

WHAT IS THE WAY TO MEASURE THE DISTANCE OF DISTANT OBJECTS LIKE STARS WITH THE HELP OF PARALLAX METHOD

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

Astronomers use the principle of parallax to measure distances to celestial objects including to the Moon, the Sun, and to stars beyond the Solar System.

See the animation below to understand the parallax method for determining the stellar distances

http://spiff.rit.edu/classes/phys240/lectures/parallax/parallax.html

Aswin Ramesh Asked (via email)
is it the same method that we use in trigonometry ?
Parallax is a different concept, though we are using the principle of trigonometry to solve problems based on it.

## What physical phenomenon is there that a black hole has a high gravity?

What physical phenomenon is there that a black holehas a high gravity?

## Relative Dimensions

Could u pls read my below theory of the universe [Ramkumar posted this]

and pls contact me when done with ur real frank comments…..

Assumption:Matter is Infinitely divisible…

Hypothesis:
if so we can infinitely into the micro and levels…
Matter can be divided into many levels
upon their size

Theory:
this that only result of 1 level affects
the above and below levels…
the levels are consistent…
i.e the levels are complete in their sense….

this whole theory is better explained with an example.

for eg,

there is the microlevel comprising of atoms something below the micro levels
comprising of what we call ‘elementary particles’ or simply fermions comprising of leptons ,quarks etc…
and there is a level above the macro level i.e
the cosmic level comprising of planets, stars etc..

what i’m saying that we cant completly explain the macro level with the micro level  but using the resultant of the micro level…
like we say that since we see neutral things there are equal no: of protons and electrons making the macro object neutral….
we are only seeing the resultant o the micro level on the macro level…
we dont see protons ,electrons etc….

lly the resultant of the micro level
comes into the macro level and the resultant of the macro level comes  into the cosmic level….
and  vice versa ….

what i’m saying is that
we can only explain ‘things’ the micro level using the micro level only
but we can explain the micro level as a whole using the resultant of the macro level…..

its like we cant use equations in the macro level and use it in the micro[atomic] level and vise versa

i.e every level is bizarre and every level is whole….i.e complete

i.e we

summing up in simple words..:

whats happening is the deeper u go down or up… u dont have a clue of what the hell u r saying….as we can only have the resultants of the levels above and below of ‘our’ level.
and there can be infinite no: of things in each level of which we are not aware of since we only have the resultants.

and so there could me more than 11 dimensions we knw….
the universe is changing..
every lim t tends to 0 sec..
so the set of the universe can be rationally defined…
ie is there is no set of complete infinite universes…
i.e the universe is beyond all dimensions….

and clarify any douts u hav….!!

• String Theory (askphysics.com)
• What is Existence? (otterthink.wordpress.com)

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