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Official Thread For OCR Physics A G484 Jan 2011

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Angular frequency is the rate of change of the angle (as it equals omega or 2pif, which is the same as 2pi/t). Apparently same as angular velocity :smile:

Angular velocity is v = 2pifA

// Perhaps everyone reading this should check back through all the pages of speech we've had, and relax a bit. Exams over now. Go party :biggrin:

(edited 13 years ago)

Reply 241

Kooper

Original post by pianofluteftw

I thought I'd put 13, as using cos I did it from what is the maximum displacement from the mean, thus any distance will be measured from that point. If you use sin it is from 15.5 :smile:

Sorry to say it, but I think it's still 15.5 if you use cos, since cosx can have a maximum value of 1, 2.5 x 1 is 2.5, add that to 13 and you get 15.5 - but the tide goes up to 18, which that equation doesn't account for. I did the same thing!

Reply 242

Kooper

Original post by vxa1314

Perhaps everyone reading this should check back through all the pages of speech we've had, and relax a bit. Exams over now. Go party :biggrin:

Easy for you to say, I've got M2 first thing tomorrow... :frown:

Reply 243

pianofluteftw

Original post by vxa1314

Angular velocity is v = 2pifA

// Perhaps everyone reading this should check back through all the pages of speech we've had, and relax a bit. Exams over now. Go party :biggrin:

2 pi f A is maximum velocity of object, not angular.

But I agree! well I'm off to end of exams party now anyway! :biggrin:

Reply 244

swond03

Original post by FruitsPunchSamurai

That's what I did. A higher SHC below it's melting point means that it gains/ loses energy at higher rates.

I put a curve down towards 0, then flat, then sort of tailing off steeper, cos thats how cooling curves go, does this mean i got it wrong?

Reply 245

vxa1314

Original post by Kooper

Easy for you to say, I've got M2 first thing tomorrow... :frown:

M2 was easier than any other exam I've had so far. :/

Just annoyed, I ****ed up my C3. I could tell it was an amazingly EASY paper, I just ****ed up badly somehow... dunno how but I did. Nervous probably :/

N I've got dyslexia and I haven't been diagnosed so yah : /

Hope to get diagnosed by summer.

Reply 246

pianofluteftw

Original post by Kooper

But surely as you are multiplying by 't'? :smile:

Ah well

only one or two marks maybe :smile:

Reply 247

vxa1314

Original post by pianofluteftw

2 pi f A is maximum velocity of object, not angular.

But I agree! well I'm off to end of exams party now anyway! :biggrin:

V = omega R

Assuming Omega = 2piF

and R = A

Then V = 2piFA

// Kays I'm off, go party people! Don't worry. Just hope you did better or slightly better than everyone else in the grade you want.

Also: Cooling thing for milk. I didn't read whether there was heat loss, but assuming a refrigerator is well insulated, I assumed no heat loss so I did a y = -x line down, then a y = 0 line for latent heat of fusion kinda thing, then another y = -kx line down.

(edited 13 years ago)

Reply 248

729

Pretty easy paper on the whole, here are some answers I remember.

Speed of the boxes was like 1.33

Mass of Helicopter was about 1500kg

It cost about £1.41 to use the fridge

The milk lost energy at about 19 J/s

The Speed of Nitrogen was 450m/s

Reply 249

FruitsPunchSamurai

Original post by swond03

I put a curve down towards 0, then flat, then sort of tailing off steeper, cos thats how cooling curves go, does this mean i got it wrong?

I'm not exactly sure. I remember reading somewhere to assume the rate of energy loss was constant. I thought that meant to draw straight lines. :confused:

Reply 250

729

Also the Final Formula was d = 15.5 + 2.5cos((pi*t)/22500)

Reply 251

Kooper

Original post by pianofluteftw

But surely as you are multiplying by 't'? :smile:

Ah well

only one or two marks maybe :smile:

t is inside the brackets, so no matter how big it gets, cos of it can't go above one.
Still, there's no way they'll take of more than a mark for us putting 13, and by the sounds of this thread, 90% of people put that anyway!

Reply 252

vxa1314

Original post by 729

Same. I agree it was an easy paper. Same with every other exam I've had so far which I've felt like I messed up.

I got same answers as you. Just getting the answers right doesn't mean we did good though :/ We need to get all the B1 Marks and M1 Marks :O

Reply 253

Captain Hob

Definite resit. My mind just went blank for a lot of it, and I came out realising a load of crap I should've done. At least everyone else I know found it hard.

Reply 254

sulexk

Well for the frequency angular frequecy question:

"frequency is the number of oscillations a particle completes per unit time"
"angular frequency is the rate of change of angle- what's more it is the number of 2pi radian cycles completed per second by a particle"

I wonder if this would work?

Reply 255

swond03

Original post by FruitsPunchSamurai

I'm not exactly sure. I remember reading somewhere to assume the rate of energy loss was constant. I thought that meant to draw straight lines. :confused:

Ahh well, i didnt have enough time to read properly so i have no idea.
It wouldnt have been so bad if we'd had an extra half hour or so.

Reply 256

Kooper

Original post by FruitsPunchSamurai

I'm not exactly sure. I remember reading somewhere to assume the rate of energy loss was constant. I thought that meant to draw straight lines. :confused:

The textbooks all have straight lines even though it should be slightly curved due to the changing temperature difference, but to be honest I think the change in gradient would be negligible so they should be straight lines.

Reply 257

vxa1314

Original post by Kooper

90% of the people who used A = 2.5 maybe.

I used A = 5 and I still want to argue that the tides don't compress. So the equilibrium point should be where it was minimum. Therefore the gravitational pull of the moon should only pull the tides UP and it can't compress it. So the minimum amplitude should've been 13, and that it couldn't of been modeled as a SHM question since it doesn't oscillate either side.

Reply 258

Kooper

Original post by vxa1314

My teacher said you get all marks if you write just the correct answer, and I hope that's right because my methods were practically illegible!

Reply 259

vxa1314

Original post by Captain Hob

Definite resit. My mind just went blank for a lot of it, and I came out realising a load of crap I should've done. At least everyone else I know found it hard.

Felt the same with my C3 exam, go bitch at some noobs. : )

Coz you know you're cleverer than what you did.

Also I don't see how the Physics exam people today even judged how good you were at the Physics.

They used **** questions etc. They tried to be clever but failed too. I mean what the ****, Tides don't move at SHM. When you set a driving frequency on a bob on water or whatever, the water only goes down because you're applying a force DOWN for a small instant in time. Whereas the Moon only pulls it UP.