Insight exams

[thatricksta]

Has anyone else found that the relativity from insight exams (which is short answer) is really weird??

i dont know if my understanding is wrong or insight is wrong, but apparently tv=to/v if to is in light years
e.g.

you travel at 0.8c towards a planet, it takes you 20 light years
to an observer they see 20/0.8 years = 25 years...

i thought it was t_v=t_oɣ
therefore tv = 20*1.667 = 33.3 years

if someone could confirm my understanding that would be fantastic thanks

edit:
also, right now, im looking at a motion question ive done and it works through to find the right answer but then goes on to find a completely different thing (e.g. it was asking for vertical initial velocity, which it finds, but then goes on to find the angle at which its fired at, which is not even relevant) and other times it doesn't even find the answer at all =/

insight for chem are really good, wtf happened to physics?

[Lasercookie]

light years are a measurement of distance, not time.
A light year is the distance light will travel in one year
1 light year is defined as: C * seconds in a year

so:

(the c's cancel out)



edit: I think I screwed up the reference frames, can you post the actual questions you're talking about? But yeah, the thing to remember is light years = distance.

[xZero]

i just want to say that light years is a measurement of distance, not time and im pretty sure your eg. is wrong, post the question up

[Lasercookie]

edit:
also, right now, im looking at a motion question ive done and it works through to find the right answer but then goes on to find a completely different thing (e.g. it was asking for vertical initial velocity, which it finds, but then goes on to find the angle at which its fired at, which is not even relevant) and other times it doesn't even find the answer at all =/

Velocity is a vector, it includes the magnitude AND the direction. The angle at which it is fired at is the indication of its direction.

[thatricksta]

edit:
also, right now, im looking at a motion question ive done and it works through to find the right answer but then goes on to find a completely different thing (e.g. it was asking for vertical initial velocity, which it finds, but then goes on to find the angle at which its fired at, which is not even relevant) and other times it doesn't even find the answer at all =/

Velocity is a vector, it includes the magnitude AND the direction. The angle at which it is fired at is the indication of its direction.

but this is a component of velocity, its vertical...

[thatricksta]

light years are a measurement of distance, not time.
A light year is the distance light will travel in one year
1 light year is defined as: C * seconds in a year

so:

(the c's cancel out)



edit: I think I screwed up the reference frames, can you post the actual questions you're talking about? But yeah, the thing to remember is light years = distance.

ok, so if light years is a distance, then why is it not affected by length contraction of the lorenz factor? why is it just over the speed? these are questions i havent encountered up until doing insight exams (i have done all stav, neap and VCAA)

i will upload the question in just a sec

edit:
its attatched

[Lasercookie]

You can use x=vt if you're calculating the proper values (Postulate I: The laws of physics work in all inertial reference frames).

Otherwise yeah, you have to use the relativistic equations.

[thatricksta]

You can use x=vt if you're calculating the proper values (Postulate I: The laws of physics work in all inertial reference frames).

Otherwise yeah, you have to use the relativistic equations.

but isnt it from the earths point of view in this question?

[Lasercookie]

The hardest part of that question is determining what are the proper/relativistic values.

The question is asking from the Earth's point of view, so therefore the values that are proper are the ones observed on Earth.

To go about the question, I would:
Determine which values are proper or relativistic.
So, from the point of view of Earth, I'm pretty sure 20 light years will be proper, 0.8c will be proper (as it's been measured by Earth scientists).

From there you can
1. calculate the time it takes for the astronauts to get there
t=x/v=20 light years/0.8c = 25 years

2. calculate the time it takes for the message to get back (I'm assuming it's a beam of light (usually is) and therefore travels at c in all reference frames)
t=20 light years/c = 20 years

From there just add the 2200 + time to get there + time for message
=2200+25+20
=2200 + 25 + 20
=2245

I have a feeling that I'm making a mistake somewhere.
Edit: Nope, I'm confident that my working out is correct. What did the solutions they give you say?
You should also be aware that you're doing a trial from the older study design, the 2009-2011 Insight exams have purely multiple choice for Special Relativity

[thatricksta]

The hardest part of that question is determining what are the proper/relativistic values.

The question is asking from the Earth's point of view, so therefore the values that are proper are the ones observed on Earth.

To go about the question, I would:
Determine which values are proper or relativistic.
So, from the point of view of Earth, I'm pretty sure 20 light years will be proper, 0.8c will be proper (as it's been measured by Earth scientists).

From there you can
1. calculate the time it takes for the astronauts to get there
t=x/v=20 light years/0.8c = 25 years

2. calculate the time it takes for the message to get back (I'm assuming it's a beam of light (usually is) and therefore travels at c in all reference frames)
t=20 light years/c = 20 years

From there just add the 2200 + time to get there + time for message
=2200+25+20
=2200 + 25 + 20
=2245

I have a feeling that I'm making a mistake somewhere.
Edit: Nope, I'm confident that my working out is correct. What did the solutions they give you say?
You should also be aware that you're doing a trial from the older study design, the 2009-2011 Insight exams have purely multiple choice for Special Relativity

Thats correct, thanks.
I just didn't really understand it because I have never have to work with something like that

[Lasercookie]

Yeah, it is a question that requires you to think a fair bit. The thing with special relativity is that you have to remember the theory and the rules it outlines. If your working out violates the ideas, than what you have done is incorrect.

The stuff on the VCAA exams are a lot easier, multiple choice means you can pretty much eliminate most of the choices immediately (on some trials you could eliminate most of the questions down to one choice *cough*TSFX*cough)

[thatricksta]

Yeah, it is a question that requires you to think a fair bit. The thing with special relativity is that you have to remember the theory and the rules it outlines. If your working out violates the ideas, than what you have done is incorrect.

The stuff on the VCAA exams are a lot easier, multiple choice means you can pretty much eliminate most of the choices immediately (on some trials you could eliminate most of the questions down to one choice *cough*TSFX*cough)

Yeah thanks. I definitely agree with what your saying; the exams that I have done with m/c are very easy!