please help! (1 Viewer)

[piyo_extreme]

a star is 100 light years away from a planet where a rocket takes off at .99c. how far away is the star in the rockets frame of reference and how long does it take to reach the star, also in the rockets frame of reference?

 

[Captain Gh3y]

Length contraction formula (since length contraction also applies to the perceived distance to an object)

lv = lo*sqrt(1-v²/c²)

Distance to star as observed on rocket = 100*sqrt(1-99²)

= 14.11 light years (2dp).

t = s/v

t = 14.11/.99

= 14.25 years.

According to the people on the rocket, as the question asks.

 

[serge]

Length contraction formula (since length contraction also applies to the perceived distance to an object)

lv = lo*sqrt(1-v²/c²)

Distance to star as observed on rocket = 100*sqrt(1-99²)

= 14.11 light years (2dp).

t = s/v

t = 14.11/.99

= 14.25 years.

time from who's perspective?
dont you need to dilate it as well?

 

[Captain Gh3y]

time from who's perspective?
dont you need to dilate it as well?

I'm not sure. It said time from the perspective of the people on the rocket, so I don't think you would, you just need to use the dilated distance.

 

[serge]

I'm not sure. It said time from the perspective of the people on the rocket, so I don't think you would, you just need to use the dilated distance.

also in the rockets frame of reference?

your calculations are good but time should be dilated i think

so it is 100.9 light years

length cant contract without time dilating

 

[Captain Gh3y]

I said 14 years because they only need to travel 14 light years, not 100, due to length contraction.

 

[MaximusVII]

captains method is correct or u can do it ur method which takes longer, both methods get the same answer

 

[香港!]

your calculations are good but time should be dilated i think

so it is 100.9 light years

length cant contract without time dilating

Hmm... this is what I reckon:
From the Rockets frame of reference time doesn't dilate.
But from a reference OUTSIDE the Rocket, then time does dilate??

 

[Captain Gh3y]

Hmm... this is what I reckon:
From the Rockets frame of reference time doesn't dilate.
But from a reference OUTSIDE the Rocket, then time does dilate??

Yes, if you were outside the rocket watching them, it'd seem to take 100 years for the rocket to get there.

 

[Haku]

I said 14 years because they only need to travel 14 light years, not 100, due to length contraction.

length contraction is a BS concept. the length to the rocket contract due to the dialation of time. first u find out the time needed to travel by time dialation formula, and use that time to calculate the distance that the rocket record.

i agree with serge.

 

[helper]

This is getting into general relativity and space-time warping. Yes the travel time taken does shorten when you are travelling close to the speed of time.

 

[Haku]

so which explaination is right?

its the length contract and time contract separated, having to do two calculation useing that formula

VS

time dialation, causing the measured time to shorten, thus distance also contract. use the formula for time dialation and sub in the time times speed to get the distance the rocket experience.

 

[香港!]

^
How does "time contract"?
I nvr encountered it before @_@
I thought time only dilated lolz

 

[Haku]

^
How does "time contract"?
I nvr encountered it before @_@
I thought time only dilated lolz

lol, sorry for confusing u. i typed the wrong thing. i am changing it now,

 

[香港!]

hahaha
.........

 

[helper]

You can only use your own observations to calculate spped. You measure your time in your frame. You measure the distance in your frame.

Time dilation is occuring but you do not notice it in your own frame.