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neuromancer
Decorated

Joined: 04 Aug 2005
Posts: 168
Location: Birmingham, UK

woo!! this is my first silver, recieved this morning.

I'm an engineer, not a physicist so I'll give it a shot, but doubt my answer will be correct!!!
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Posted: Mon Nov 28, 2005 11:24 am
ALISDAIRPARK
Unfictologist

Joined: 27 Nov 2005
Posts: 1646
Location: Everywhere else

I'm also not a physicist, but this my thoughts:

 Spoiler (Rollover to View): A & B are traveling towards each other, and we need to use the Lorentz formula for the answer, but as an algebraic formulae with ALo = 5BLo . Again it's been years since I studied maths so I'm rusty, but this is what I get it down to c=(5vB-vA)/4 but I can't translate this to vA+vB as a fraction of c...

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Posted: Tue Nov 29, 2005 12:57 am
timair
Boot

Joined: 13 Dec 2004
Posts: 46
Location: Cambridge-UK 69/333

 Ashin wrote: "What is the relative speed of the two observers as a fraction of the speed of light?" I do not actually have the card (yet), but I am definitely 100% on my answer. Also, I believe this card is written incorrectly, because in order for any calculation to work, both scientists have to be traveling perpendicular to the disc's axis. I'm about to send off an email to Mind Candy about this.

I don't see why they have to travelling perpendicular to the disc's axis.

The way I read it they are both travelling towards the disc along its axis (after all this is what the card says) at different speeds but in the *same* direction.

One of them is travelling faster than the other so goes past the slower one at some point in time before reaching the disc.
Due to relativistic effects at that point in time the disc seems to be different sizes to the two observers.

At least one of them must travelling a significant fraction of c for there to be a 5 times size effect.

The question asks "What is the relative speed of the two observers"

So does it want the difference in speed between them, or their two speeds towards the disc?

Also bear in mind the Lorenz equation is talking about a body contracting when *that* body is travelling at relatavistic speeds.

I'm no expert but I don't think this in necessarily the effect at work in this scenario. The disc is stationary.
So there must be some effect that changes what an observer sees when they are travelling near the speed of light that makes things seem bigger or smaller than normal.
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Posted: Tue Nov 29, 2005 5:57 am
ALISDAIRPARK
Unfictologist

Joined: 27 Nov 2005
Posts: 1646
Location: Everywhere else

yeah, I've done some more reading too.

The card does not specify if they are travelling in the same direction, so it could be either... but the big thing confusing me is they are travelling TOWARDS the disc, so the Lorentz equation does not apply, and I can't find anything that indicates any perceived shrinkage when travelling towards an object.
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Posted: Tue Nov 29, 2005 7:03 am
timair
Boot

Joined: 13 Dec 2004
Posts: 46
Location: Cambridge-UK 69/333

 ALISDAIRPARK wrote: The card does not specify if they are travelling in the same direction, so it could be either...

No but it says they are both travelling towards the disc along its axis (which is a single straight line coming out of it either side) If they pass each other and are going in different directions then one of them will be going *away* from the disc not towards it.

So I personally think they have to be both going in the same direction.

 Quote: but the big thing confusing me is they are travelling TOWARDS the disc, so the Lorentz equation does not apply, and I can't find anything that indicates any perceived shrinkage when travelling towards an object.

I found a site a site that explains all the Lorenz contraction stuff quote well, but the "What things look like to and observer travelling at near light speeds" was in the TODO section
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Posted: Wed Nov 30, 2005 6:14 am
CreamCheese
Kilroy

Joined: 30 Nov 2005
Posts: 2
Location: Woking, UK

LOL i'm only an A level physics student and I just solved it!!!

 Spoiler (Rollover to View): You don't need all that complex stuff, Just draw a picture and use some common sense

Posted: Wed Nov 30, 2005 8:35 am
chichiri
Decorated

Joined: 31 Oct 2005
Posts: 207

you were beaten to it though!!!!

no da

Posted: Wed Nov 30, 2005 8:43 am
CreamCheese
Kilroy

Joined: 30 Nov 2005
Posts: 2
Location: Woking, UK

I'm happy with second place

Posted: Wed Nov 30, 2005 8:46 am
chichiri
Decorated

Joined: 31 Oct 2005
Posts: 207

It says solitair was first to solve this, but solitair is not on the first ten solves list, nor is it listed as solved on his profile!!!

no da

Posted: Wed Nov 30, 2005 8:50 am
Wowbagger
Boot

Joined: 22 Aug 2005
Posts: 69
Location: Leafy Surrey, UK

He's been doing so well maybe the website just assumes he's solved everything!

Posted: Wed Nov 30, 2005 9:17 am
ALISDAIRPARK
Unfictologist

Joined: 27 Nov 2005
Posts: 1646
Location: Everywhere else

It would help us non-physics people if there was a hint/ spoiler...
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Posted: Wed Nov 30, 2005 9:36 am
solitair
Boot

Joined: 15 Aug 2005
Posts: 28
Location: Rushden, UK

Well as far as I know I haven't had a sucessful solve accepted.

But then a number of the solve pages are a little mixed up about who solved what first. It may be that one of my previous answers was accepted in some way but didn't register. or perhaps it's also registering incorrect attempts?

Posted: Wed Nov 30, 2005 10:39 am
Ashin
Veteran

Joined: 22 Nov 2005
Posts: 140

I wish my cards would come in the mail so I can see if I got this one....

I'm at a disadvantage to most of you since I live in the US, the cards are not readily available to me.

I have to say though that I disagree with you ALISDAIRPARK about spoilers on silvers. This is a competition of sorts, after all there is a prize, and it definitely seems that the silvers are going to be the great separator, so it seems kind of pointless to share the answer to silvers since it completely removes the competition factor...

As for hints though, most certainly, but I stick by my original hint(s) on page 1. I know what I'm talking about.

Posted: Thu Dec 01, 2005 1:23 am
TheBozzball
Boot

Joined: 29 Nov 2005
Posts: 12

I emailed the perplexcity people about the problem with "This card was first solved by". It currently puts up the name of the first person to suggest a solution. They will be changing the site shortly so that this problem does not exist.

Posted: Thu Dec 01, 2005 3:06 am
ALISDAIRPARK
Unfictologist

Joined: 27 Nov 2005
Posts: 1646
Location: Everywhere else

I kinda understand your point Ashin, however I do not think the points are part of the main competition (for the money).

My view is the Forum is here for us to help each other, regardless of the colour/ points at stake. Otherwise it would only be a place to gloat when you have the answer? But respect your choice.
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Posted: Thu Dec 01, 2005 6:47 am
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