OCR Forces and Motion (Jan 11)

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Reply 40

Blundell

Ok I'm a bit annoyed nobody knows the actual answer but I might get 1 mark because I got 'mixed up' :p:

Reply 41

Vjyrik

Gaah, the lift question, I didn't like it very much...
I wrote:
1) Highest pressure while accelerating up
2) Lower pressure while at constant velocity
3) Lowest pressure when decelerating

Reply 42

Vjyrik

... or would it be with: acceleration at the lower pressure, terminal velocity at a higher pressure and te deceleraiton at the lowest? :P
Damn, I just hate having to think about it...

Reply 43

Nikki.x

oh dear...
i completely screwed up this paper.. reading what you guys have put my answers are wayy off.
i completely froze on the first few questions eventhough they were 'easy'.

do you reckon the grade boundaries would be dropped? i hope so.

i thought the paper was quite hard... grr, so depressed about it :frown:

xxx

Reply 44

Lady Justice

Hah yeah I thought it was hard too, all of my class seemed to run out of time.

The hardest ones for me were the explaining pressure as a result of acceleration, and I think the angle one on the last question that was deceleration 5.5 ... I was convinced I knew how to do it but I kept getting 6 point something :s-smilie:

The Young Modulus question (how many marks was that, 12?) hopefully made up for me seriously running out of time... it was like free marks :smile:

And Joules per second will DEFINITELY be accepted instead of Watts???

Reply 45

Livinglegend

I think the grade boundaries wont change from last year...they may well go up as the youngs modulus and question were direct gifts...saying that...the penultimate question along with the lifts accelaration...not nice...

Reply 46

studentag2

What were the grade boundaries for last year? Was it exactly 48/60 to get an A or was it less?

Cheers! :rolleyes:

Reply 47

QE5

I'm taking this exam in June, as I need more time.

How difficult was this paper compared to past papers?

Reply 48

LuluMumma

QE5

I'm taking this exam in June, as I need more time.

How difficult was this paper compared to past papers?

Compared to past papers I would say it was hard. I was getting As in past papers but I won't be getting one now! It also seemed quite long as I didn't have enough time.

Reply 49

Nikki.x

yeah i thought it was quite hard.
i had trouble with timing too, i didn't have time to go back to previous questions which was well annoying because i missed some. grr!

i am so expecting a C (if i'm lucky!)
don't think physics is for me haha.

i'm sure all of you would have done well :smile:

but if not, grade boundaries will be dropped, so it's win win situation haha.

xxx

Reply 50

Jeykayem

I'm so glad the long essay type question was on Young's modulus! I think I finally (just about) understood all the forces that act on a car the day before the exam but I would still have panicked slightly if there had been a twelve mark question all about braking forces. I don't think the paper was as hard as I've found some of the past papers to be, although I missed a few marks because I didn't have time to finish all the questions.

I had a Physics lesson just after the exam and we went straight into doing Electrons and Photons. My teacher had written a message on the board before we came in, saying, 'No I have NOT seen the paper. Yes I'm sure it WAS very hard. No we will NOT be discussing it'. :smile:

Reply 51

studentag2

Hi there,
For the last question regarding the braking distance, I got 48 m and something. I don't know if I did it right as I got something different to other pple.
Basically how I worked it out was, firstly i found the kinetic energy of the car; 1/2x 850 x 25(2). That would equal to the work done by the brakes to stop the car, so f x d = kinetic energy.
They gave the braking force of 5520 something, so d = KE/ 5520.

Have I done this correct or was the braking force different? I've heard that pple got 56m, but I got 48m. I can't really see why this method isnt right. If anyone could see whre i went wrong, or if whether or not i'm rigth...i'd greatly appreciate it,,
Many Thanks :smile:

Reply 52

Vjyrik

studentag2

Erm.... If you did that, you should have considered the vertical components of weight or something, because the car would gain/lose energy while moving on a slope.

If I recall the question correctly, I did use kinematics:
v^2 = u^2 + 2as
-> s = (v^2-u^2)/2a
-> v = 0 ms^-1
-> s = (-u^2)/2a
you know 'u' and 'a'

Not prefectly sure if I'm right though :P

Reply 53

Livinglegend

You had to use suvat as the accelaration was = 5.5 ms^-2
If you got 48 you probably used the wrong distance of the slope. ie the horizontal instead of the hypotenuse. Saying that; the Mark scheme should still give credit for the method you used.

Just wondering...was the lift question about pressure increase/decrease during accelaration worth 2 or 3 marks?

Reply 54

yosy

i did the same thing and unfortunately, it is incorrect. u hav 2 do resolve it horizontally and minus that from 5520 and equate that to 1/2MV2 or so i didnt realise that it was one of those m1 things because of bloody timing. is it me or did anyone else have the same problem?????

btw i KNOW the grade boundary for the following series (its on the ocr exam reports go to the website) :

june 07: 45/60-- it was very straight forward
Jan 07: 43/60-- not as straight forward with the projectile description and the final question

Jan 08 seemed Different! so it probably for benefit of the country will be like Jan 07 and stay at 43/60 (72%) for an A

Reply 55

rdu11

Arghhh
I got completely the wrong end of the stick on the end of the first question so i got off to a great start really!!
And a really dislike vectors and that vectors question, the tension one i did not get at all!
But one positive i liked the Young Modulus question! that was all good!
But i'm proberly going to have to resist it in June...

Reply 56

studentag2

The lift question was worth just 2 marks. By the way for the grade boundaries Yosy stated, does that mean last year they only needed 72% for an A? Whats the difference between Raw and UMS?

Thanks

Reply 57

Livinglegend

Ooh thanks. Erm...Raw marks are the actual marks on the paper. UMS marks or Scaled marks are the marks that correspond to each raw mark.

Since some years the papers are harder than other years; they have UMS marks to ensure that a grade A in 2000 is as difficult to obtain as in 2007. The UMS marks are always adjusted so that a= 80% b=70% and so on for all subjects.

Thus, you can get full UMS marks by getting less than 100% on the paper. Simlilarly; you can get 80% UMS marks ie 72 in this paper by getting less than 80% of raw marks (normally around 43-46 on this paper)

Hope that helps. If ya still dont get it...theres numberous threads on tsr about this; just give it a quick search :wink: