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# OCR PHYSICS B G492~ 9rd June 2014~ AS Physics Watch

1. (Original post by emfp21)
All I know is to subtract the observer's velocity from the other :/

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So when two objects are travelling in multiple planes i.e one car going north and another car going east, how would you work out the north-going car's relative velocity to the east-going one? Apologies if this is a dumb question and/or I am not making any sense.
2. (Original post by Argetlam)
I think spread is half of the range. The resolution is the smallest change an instrument can detect. Hope that helped
thanks, so essentially spread = uncertainty
3. (Original post by kittyoliviam)
In phase and out of phase seems to consistently be in the mark schemes, and works for standing waves and superposition in general.
What do you mean by in phase and out of phase in terms of standing waves?
4. (Original post by Roob77)
So when two objects are travelling in multiple planes i.e one car going north and another car going east, how would you work out the north-going car's relative velocity to the east-going one? Apologies if this is a dumb question and/or I am not making any sense.
You add the vectors tip to tail. In that example, because north and east are perpendicular you can use Pythagoras' theorum. So if they were going at 30mph, then the resultant would be root 1800 NE (that's root 2*30^2)
5. (Original post by blackwatersun)
In terms of sig figs, unless there is a clear indication otherwise, stick to 3sf and you will never be penalised. The exception is uncertainty, where you must always go to 1sf fewer than the measurements (unless the measurements are 1sf, obviously).

I hope standing waves don't come up, I find then the most difficult part of this topic because you're never exactly sure what the question is asking you to explain. And bring on the mechanics! I did M2 for further maths a couple of weeks ago so physics mechanics seems peachy!
How do you know this? Isn't this incorrect if the data is given to fewer sf?
6. (Original post by Carla Huynh)
You add the vectors tip to tail. In that example, because north and east are perpendicular you can use Pythagoras' theorum. So if they were going at 30mph, then the resultant would be root 1800 NE (that's root 2*30^2)
Ok thanks, I think I may have just been over complicating things in my head as that seems really simple :P
7. (Original post by Carla Huynh)
What do you mean by in phase and out of phase in terms of standing waves?
it is better to describe it as a node, which is constantly exactly out of phase so doesn't move i.e zero displacement. Then antinodes which have a varying amplitude going in and out of phase so it wobbles i.e maximum displacement is present as well as zero displacement. if the makes sense?
8. (Original post by qivo)
it is better to describe it as a node, which is constantly exactly out of phase so doesn't move i.e zero displacement. Then antinodes which have a varying amplitude going in and out of phase so it wobbles i.e maximum displacement is present as well as zero displacement. if the makes sense?
Ah ok that makes sense. So if your asked to describe a standing wave what would you say?

something like an incident wave and reflected wave travel in opposite directs and interfere. At places where they always interfere destructively nodes are formed and at places which vary between constructive interference and destructive interference are antindes. Would that score full marks? :/
9. (Original post by Carla Huynh)
Ah ok that makes sense. So if your asked to describe a standing wave what would you say?

something like an incident wave and reflected wave travel in opposite directs and interfere. At places where they always interfere destructively nodes are formed and at places which vary between constructive interference and destructive interference are antindes. Would that score full marks? :/
that is what i would put anyway, depends what particularly the question is asking really
10. (Original post by Carla Huynh)
Ah ok that makes sense. So if your asked to describe a standing wave what would you say?

something like an incident wave and reflected wave travel in opposite directs and interfere. At places where they always interfere destructively nodes are formed and at places which vary between constructive interference and destructive interference are antindes. Would that score full marks? :/
Just look at my post last page or the page before that, I wrote pretty much the perfect answer to any staanding wave question or at least i think i did, don't want to be vain aha
11. (Original post by Roob77)
So when two objects are travelling in multiple planes i.e one car going north and another car going east, how would you work out the north-going car's relative velocity to the east-going one? Apologies if this is a dumb question and/or I am not making any sense.
If the car is going north at a certain speed, this is the same relative to the east going car as the north going car being stationary, and the east going car travelling south at the same speed as the north car was travelling originally. So you subtract the north going car's velocity from both vehicles, and then use pythagora's theorem to add the 2 velocities.
Without a diagram I don't think there is a simpler explanation than that.
12. Everyone feeling confident? Seems pretty straight forward, one day of revision, 5 past papers and a few revision guides digested and I reckon tomorrow should be alright But then again you never know considering the monstrosity that was G491
13. Does anyone know if we get access to the pre-release articles in the exam?
14. (Original post by Cluck)
Does anyone know if we get access to the pre-release articles in the exam?

Did your school never supply you with one....?
15. (Original post by shloke123)
Guys, click on the link below and scroll to the bottom, there are questions and answers for predicted section C questions

http://matthew-arnold.tmp.synergy-le...view.php?id=62
Hey, have you done set #1a question 9(h)?
It gives the answer as 1 / 2^8
If so would you mind explaining? Thanks
16. (Original post by Jamie001)
Hey, have you done set #1a question 9(h)?
It gives the answer as 1 / 2^8
If so would you mind explaining? Thanks
I doubt this will come up because its testing g491 more really but it's just saying that because there are 2^8 alternatives, if the voltage value lies between two possible alternatives, the most it can be wrong is one in 2^8 because it's rounded to the nearest voltage value.
actually I guess since it's rounded to the nearest one it should actually be 0.5/ 2^8?! But these questions aren't official anyway they were made up be a teacher for practise so I wouldn't worry too much
17. 2^8 is the voltage resolution, so for anyone 1 level, the the amount that the sound can vary by is 1/2^8. It can range anywhere in that number between levels without being detected, as soon as it surpasses that level, it will be dtetected as a different level. I probably sound really cryptic sorry
18. Yh as carla said, I doubt it will come up. Just make sure you know your quality of measuremen,t and all of g492 and the exam should be simple enough
19. (Original post by Hornet_96)

Did your school never supply you with one....?
Thanks but I have a copy, I was just wondering whether we would get one in the actual exam
20. (Original post by Cluck)
Thanks but I have a copy, I was just wondering whether we would get one in the actual exam
Yup, it says we'll be given a fresh copy.

My school's organisation is crap though, they lost the formula booklets so we had to start 20 minutes late for G491

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