Length contraction (1 Viewer)

[Roy216]

Relativity is a mind fucker, anyway I need some help with some questions with length contraction which I'm not feeling confident in.

1. A space shuttle is 30 m long and the orbits the earth at about 30 000 kph. Calculate its apparent length as seen by an astronaut on Earth.

2. Continues from question 1, An astronaut in the same space shuttle looks down and sees a 250km section of the great wall of china.
(a) Calculate the length of the section as seen by th astronaut
(b) If the astronaut saw the section to be 250km long, calculate its real length on earth

 

[IamBread]

Relativity is a mind fucker, anyway I need some help with some questions with length contraction which I'm not feeling confident in.

1. A space shuttle is 30 m long and the orbits the earth at about 30 000 kph. Calculate its apparent length as seen by an astronaut on Earth.

2. Continues from question 1, An astronaut in the same space shuttle looks down and sees a 250km section of the great wall of china.
(a) Calculate the length of the section as seen by th astronaut
(b) If the astronaut saw the section to be 250km long, calculate its real length on earth

1.





2.

 

[someth1ng]

IamBread, for the second part:

Is it basically:
- If you're looking at something in relative motion, you're looking for Lv
- If you're look at something "stationary", you're looking for Lo

Is this right?

 

[Timske]

Inertial frames of reference. Lo is the rest frame that is the measurement of length taken at rest, not moving or steady motion. so yes if you're looking at something 'stationary' its Lo. and Lv is the length of an object measured from a different frame of reference.

 

[Roy216]

i got the answers, all it is is figuring out Lv and Lo but Lv = measurement from an outside frame of reference Lo = length of object within frame

 

[Roy216]

Btw IamBread i got 37.99 not 29.99 for question 1

 

[someth1ng]

I think of Lo as what the real length is and Lv as what is perceived.

 

[nightweaver066]

Btw IamBread i got 37.99 not 29.99 for question 1

It is 29.99m.

Post your working out if you are still unsure.

 

[Roy216]

Lo = 38 v = 8333.33 Lv = ?

Lv = 38 (Root) (1-(8333.33^2/c^2))
= 37.99

I asked a couple people in my class they got the same thing

 

[Roy216]

yea thats pretty much it

 

[Roy216]

oh woops i made a typo it was 38 instead of 30 my bad

 

[IamBread]

IamBread, for the second part:

Is it basically:
- If you're looking at something in relative motion, you're looking for Lv
- If you're look at something "stationary", you're looking for Lo

Is this right?

That's about right, but "If you're look at something "stationary", you're looking for Lo" isn't really the best wording lol. If the question says "this is how long you see it in your FOR, how long is it in the objects FOR?" Then you are looking for Lo. Though I can never remember which Lv and Lo are, so I just quickly figure out what my answer should be, ie, for the example I gave the length should be longer so I go from there. Probably not the best way to do it though.

 

[someth1ng]

You know, that makes sense now...after taking a good long sleep.

It's not really necessary for me to know it yet since my school hasn't done space yet (Motors & Generators-->Ideas to Implementation-->Space-->Astrophysics).

 

[Timske]

For example If an observer measures the length of a train then its Lo because its meaaured from his reference. If the traveller in the train measures the length of the station itll be Lo as well because its measured from his reference. Because the train is moving in steadymon. Depends on what the q wants