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# Official Thread For OCR Physics A G484 Jan 2011 Watch

1. Didn't really like that Lost all the marks on the sattellite one. I know how to do it now - frustrating.

Hoping for lower grade bounderies then in june, what'd you all think?
2. (Original post by nirvana001)
the question were u had to describe differences between displacement and amplitude and frequency and angular frequency was stupid and hard :/

wot do u guys think full UMS is likely too be? 53,54,55?
I gave M2 definitions rofl.

Frequency, Oscillations per unit time.

Angular Frequency = Omega = Rads-1 so therefore it's the change in radians per second.
3. (Original post by pianofluteftw)
The amplitude was indeed 2.5, and I put the displacement being x=2.5cos(2pif)t + 13 (I think f was 1.22x10^-5) and wrote a note to the examiner saying it must be from the maximum or minimum.
Same! Except I think it's +15.5 rather than +13 since that's the equilibrium position.

Also, according to my spellchecker when I wrote equilibrium above, i can't spell it, so there goes my QWC mark.
4. (Original post by pianofluteftw)
Well, for starters while kWh is not on the syllabus, it does STATE that all previous knowledge is assumed (Gave me a nice easy few marks!)

The amplitude was indeed 2.5, and I put the displacement being x=2.5cos(2pif)t + 13 (I think f was 1.22x10^-5) and wrote a note to the examiner saying it must be from the maximum or minimum.

And the tide does illustrate simple harmonic motion! Not only springs do (I mean a woodwind instrument is a prime example). As long as acceleration is directly proportional to displacement, and is always directed towards the mean it shows simple harmonic motion. Not just springs.

And the satelite one was easy, just equate gravitational force to centripetal force and rearrange having cancelled the small 'm's and the radius.

Bit of a weird paper but none of it hard... or is it just me that thought that? Plus we'd done both Jan and June '10 past papers and specimen and it wasn't really any harder and all on syllabus?

for the displacement i put x=2.5cos(2pi f t) +15.5

i had +13 at first but pretty sure its +15.5 because it from its equilibrium point
5. (Original post by vxa1314)
I gave M2 definitions rofl.

Frequency, Oscillations per unit time.

Angular Frequency = Omega = Rads-1 so therefore it's the change in radians per second.
for the frequency 1 i sed like it depends of the time of the oscillaions and is therefore independent in SHM. for the angular velocity i sed it depends on the angle and on the frequency :/
6. (Original post by Kooper)
Same! Except I think it's +15.5 rather than +13 since that's the equilibrium position.

Also, according to my spellchecker when I wrote equilibrium above, i can't spell it, so there goes my QWC mark.

You're probably correct, I don't think he is.

If he used 2.5 instead of 5 for A, there's no way +13 would be correct.

As +13 is correct for A = 5. Not 2.5

I bet he didn't even stick it back into the equation to check.
7. (Original post by Kooper)
Same! Except I think it's +15.5 rather than +13 since that's the equilibrium position.

Also, according to my spellchecker when I wrote equilibrium above, i can't spell it, so there goes my QWC mark.
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
8. (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
Good point.

+1
9. (Original post by nirvana001)
the question were u had to describe differences between displacement and amplitude and frequency and angular frequency was stupid and hard :/

wot do u guys think full UMS is likely too be? 53,54,55?
i had no idea on angular frequency so i just defined frequency.

I think i got the first one spot on, but you just know the OCR mark scheme will have green elephant or something stupid underlined as necessary for the mark!
10. (Original post by vxa1314)
I gave M2 definitions rofl.

Frequency, Oscillations per unit time.

Angular Frequency = Omega = Rads-1 so therefore it's the change in radians per second.
i sed frequency depended on time period so independent in SHM then for the angular frequency i sed that it depended on the angle and on the frequency :/
11. 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
12. Not gonna lie, saw the helicopter through the front of the exam paper and my first thought was: fml.
13. Ahh! I think I just figured out the milk cooling graph!! It should have been a straight line negative gradient, then a flat line because it changes state, then another straight line with a steeper negative gradient!! Lost marks
Did anyone actually do that or am I crazy?
14. OCR know how to **** things up. I mean, first chemistry, and now this. It wasn't that bad of a paper, but what the **** is kilowatt hours doing in here? What is the definition for it? I just said it was 3.6x10^ something Joules. That SHM question with the tides was **** as well, read minutes instead of hours, so my calculations were all wrong. Realised my mistake at the very end and fixed it, but got the amplitude wrong etc etc.
15. (Original post by OmegaPhoenix)
Ahh! I think I just figured out the milk cooling graph!! It should have been a straight line negative gradient, then a flat line because it changes state, then another straight line with a steeper negative gradient!! Lost marks
Did anyone actually do that or am I crazy?
That's what I did. A higher SHC below it's melting point means that it gains/ loses energy at higher rates.
16. I got the milk gradient thing fine, took a while to think of which one had the steeper gradient. How did people to the boyle's law graphs? I had like a y=1/x graph for the one on the left, then a y = x one for the one on the right?

How did you work out the mass of the helicopter oO?
17. A kWh is the amount of energy consumed if work is done at an average rate of 1 kilowatt in one hour.
18. (Original post by ViralRiver)
OCR know how to **** things up. I mean, first chemistry, and now this. It wasn't that bad of a paper, but what the **** is kilowatt hours doing in here? What is the definition for it? I just said it was 3.6x10^ something Joules. That SHM question with the tides was **** as well, read minutes instead of hours, so my calculations were all wrong. Realised my mistake at the very end and fixed it, but got the amplitude wrong etc etc.
The SHM one was hard, but fine. There was a very similar question in the SHM spreads in the book.
19. (Original post by ViralRiver)
I got the milk gradient thing fine, took a while to think of which one had the steeper gradient. How did people to the boyle's law graphs? I had like a y=1/x graph for the one on the left, then a y = x one for the one on the right?

How did you work out the mass of the helicopter oO?
Yes, I got the same graphs.

Mass of helicopter - it is stationary, thus the forces are balanced. You worked out the force of the air (Ft=mv-mu) and thus force of weight of helicopter must be equal. F=mg, so assuming g is 9.81 (which I'm pretty sure we can) you can work out the mass.
20. (Original post by vxa1314)
You're probably correct, I don't think he is.

If he used 2.5 instead of 5 for A, there's no way +13 would be correct.

As +13 is correct for A = 5. Not 2.5

I bet he didn't even stick it back into the equation to check.
I know I'm right now, but I actually put 13 in the exam! I think loads of people added on 13, and then were pleased with themselves to have noticed it needed extra height, and didn't give it a second thought. At least that's what happened to me!

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