2003 HSC Multiple Choice (1 Viewer)

[ronnknee]

5. An astronaut set out in a spaceship from Earth orbit to travel to a distant star in our galaxy. The spaceship travelled at a speed of 0.8 c.When the spaceship reached the star the on-board clock showed the astronaut that the journey took 10 years.

An identical clock remained on Earth. What time in years had elapsed on this clock when seen from the astronaut's spaceship?

A) 3.6
B) 6.0
C) 10.0
D) 16.7


I chose the answer D
For some reason in Success One, it says there's no answer to it haha
Weird

 

[lyounamu]

5. An astronaut set out in a spaceship from Earth orbit to travel to a distant star in our galaxy. The spaceship travelled at a speed of 0.8 c.When the spaceship reached the star the on-board clock showed the astronaut that the journey took 10 years.

An identical clock remained on Earth. What time in years had elapsed on this clock when seen from the astronaut's spaceship?

A) 3.6
B) 6.0
C) 10.0
D) 16.7


I chose the answer D
For some reason in Success One, it says there's no answer to it haha
Weird

lol, no answer????

Check out the www.boardofstudies.nsw.edu.au
for multiple choice answer. You can find that from marker's comment.

 

[Graceofgod]

Yeah this question was screwed up and was excluded. Think about relativity.

How does the astronaut see the clock?

Anyway, assuming he could somehow see the time on the clock instantly ignoring the fact that light travels.
According to the astronaut, earth has gone at 0.8c in the other direction.
For this reason the time elapsed on the earth clock according to him would be less.

 

[obimoshman1234]

they say B. However success one has it as no answer because the actual correctly calculated answer is not there.

i mean did u actually calculate or did u just look and guess??

 

[Graceofgod]

they say B. However success one has it as no answer because the actual correctly calculated answer is not there.

i mean did u actually calculate or did u just look and guess??

The actual calculated answer is not there because the time for the light to travel is not factored in.

 

[JamesTockuss]

I believe it was not counted in the marking because the question is ambiguous - it doesnt say whether the astronaut has slowed down yet or whatever

 

[Graceofgod]

I believe it was not counted in the marking because the question is ambiguous - it doesnt say whether the astronaut has slowed down yet or whatever

I don't think so.
That is just being overly pedantic..

 

[Graceofgod]

This confusion arises regularly in discussions on Special Relativity. The word "when", as used here, implies that simultaneity is absolute. One of the important conclusions of Special Relativity is that simultaneity is relative. This is explained in any introduction to SR, or on my web page Special Relativity. So yes, the question as written is meaningless. I am informed that it was not included in calculating marks.

I think you have misunderstood what they mean by the word "when".

http://www.phys.unsw.edu.au/~jw/FAQ.html

 

[ghost-blade]

i also got D by just simply using the time dilation formula, it makes sense as more time will pass on earth relative to the astronaut.

 

[Zeber]

There was a question similar to this in one of the previous threads.

The correct answer is B) 6 years.

THis is because in the frame of reference of the spaceship, he is 'statoinary' and earth is moving away from him at 0.8c, thus when he views a clock on earth - it would appear to go slower.

 

[obimoshman1234]

i also got D by just simply using the time dilation formula, it makes sense as more time will pass on earth relative to the astronaut.

yea but its the astronaut looking at the clock on earth not an observer on earth

 

[dwarven]

yea but its the astronaut looking at the clock on earth not an observer on earth

how can he see the clock from his spaceship if its on earth

 

[ghost-blade]

yea but its the astronaut looking at the clock on earth not an observer on earth

wat?

the astronaut is looking at his clock on the spaceship which will show him the time which HIS journey toke which will show much less time than the amount of time which has gone past on earth.

remember the atomic clock which went around the earth really fast and showed that it was 1-2 seconds behind a stationary one. same thing pretty much but the clocks on the space ship.

unless the question is really screwed and goes against what weave learnt in physics and the astronaut can somehow see the time which has passed on earth. if that then the answer would be less than 10hrs. either way its never gonna be 10years

 

[independantz]

wat?

the astronaut is looking at his clock on the spaceship which will show him the time which HIS journey toke which will show much less time than the amount of time which has gone past on earth.

remember the atomic clock which went around the earth really fast and showed that it was 1-2 seconds behind a stationary one. same thing pretty much but the clocks on the space ship.

unless the question is really screwed and goes against what weave learnt in physics and the astronaut can somehow see the time which has passed on earth. if that then the answer would be less than 10hrs. either way its never gonna be 10hrs

"What time in years had elapsed on this clock when seen from the astronaut's spaceship?"

For the astronaut to view time on earth , the time it takes for light to travel from the earth to the astronauts eyes needs to be factored into the calculation as the astronaut is at a large distance from the earth.

 

[axlenatore]

how can he see the clock from his spaceship if its on earth

It could be a very big clock, maybe this is set in the future and the tectonic plates shift in such a way as to turn the countries into a giant clocks for a particular time zone

 

[CRANK-SHAFT]

well....i dont know what the fuss is...

using the time dilation equation and taking astronaut as the rest frame...we get 16.7 years for the clock on earth since thats the relative frame of reference ...if that makes sense.. .

 

[Graceofgod]

It is interesting how little people understand relativity.

Ok I will clear this up for the LAST time. -_- This is very simple.

1. The astronaut is the observer. According to his frame of reference, the earth has moved at 0.8c in the other direction. Applying the time dilation formula results in answer B. NOT answer D.

2. The original purpose of this thread was to discuss why this question is invalid. It is obvious from people still posting answers that they either don't read what other people post or they are too thick to understand one of the primary principles of relativity.

Sorry the stupidity of some people is really getting to me.

Read the thread before responding please.

 

[obimoshman1234]

It is interesting how little people understand relativity.

Ok I will clear this up for the LAST time. -_- This is very simple.

1. The astronaut is the observer. According to his frame of reference, the earth has moved at 0.8c in the other direction. Applying the time dilation formula results in answer B. NOT answer D.

2. The original purpose of this thread was to discuss why this question is invalid. It is obvious from people still posting answers that they either don't read what other people post or they are too thick to understand one of the primary principles of relativity.

Sorry the stupidity of some people is really getting to me.

Read the thread before responding please.

lol i know how u feel PEOPLE READ THE UESTION CAREFULLY and think irregardless of logic what it is saying