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# M2 Jan 2012 Edexcel - Post exam discussion - Solutions and paper in first post Watch

1. Yeah that paper was easy! I can usually only scrape 50/75 in M2 papers but I think I got a minimum of 65/75 there. (Lost marks on 2c and 7b)

For 2c I did the integration correctly, found the right constant but I took away two instead of adding two to get 11i-66j, how many marks would I lose? Hopefully no more than three...

For 7b I got 11.2ms-1... but I still got the answer to c right!

God all mechanics papers should be this easy.
2. What about sig figs. Is it always three sig figs unless g is involved in which case 2? I don't want to drop a silly mark for sig figs-could be 5 ums marks
3. I mixed up the speeds of A and B on Q6a :s
How many marks lost for that?
Also then for part c will i get ecf if ive taken the wrong speed? Method is the same as yours, except i got 5u/36 which corresponds with the factor of 5 i am out by taking the wrong speed :/

For question 7, i rounded the time to 2sf as g is approximated to 2sf.. so my time is 1.8
then for b, i used v^2 = u^2 + 2as, where s=h=3t. and got the vert speed as 6.18, which then means my answers for b and c are slightly off from yours, but still in line with my original time. How many marks will i be penalised for this, if any? my time was 0.59, maybe awrt 0.6?
This is so dissapointing as i thought this was the easiest paper i'd ever done assuming the grade boundaries are sky high,

edit: answer for 7b would be 8.6
4. A WILL BE MUCH LESS,like about 66,in our country,a lot of people screwed up,the person next to me was crying,i dnt know if scaling varies from country to country altough
5. Last June you had to get 68 for an A, what *beep* is that?! Plus in mechanics if you make one little mistake then the whole question is screw up, and you can't check your answers on a calculator like in C3 and C4! It better not be more than 68 (which is what I think I've got) this year because I don't want to retake M2 ever again.
6. hey guys, I'd really appreciate a reply. The only mistake I made was in the 3b....a really stupid mistake. I don't know what the hell I was thinking...anyways what I did is that I took 75gsin5+20 as the resistance to motion, not remembering that I had already included the gain in p.e. and added to it the gain in p.e.

i equated 2400=(75gsin5+20+75gsin5)x and found the distance AB... how many marks do you think i would lose? i got the k.e. loss, and showed my reasoning behind equating k.e. loss to p.e. gain + work done against non gravitational resistive forces..but i added values in my working.
7. For 4b, I divided 5root3/9 by 2 instead of 1, giving me a smaller angle. How many marks would I lose out of 5 for that, bearing in mind I was thinking along the right lines and did 1 - 4root3/9?
8. YES thank God the acceleration counts in vector form, that means I got 100%!
9. Hello Arsey,
All of my answers match up with yours except with the distance/energy question, foolishly I divided 2400 by 75gsin5-20 rather than 75gsin5+20, giving an answer of 54.5m. This is probably because I messed up on the work-energy principle and got the net amounts wrong. Would this be a full 5 mark drop for this? Pretty important that I get over 90 in this exam and considering the high grade boundaries people are speaking of I've gone from feeling the exam went well to getting worried lol.
Cheers
10. I hate easy papers! I think I have got 75/75 though and avoided slipping up at all. So hopefully I will get 100 which will ease the pressure on FP2 and M3 in the summer
11. In Q5 on moments, because g was used will answers to 2sf be fine?
12. For 7b. instead of using the exact time, I used my 3sf time (1.84) so I got velocity (going up to be -6.032) and used this to get a speed of 8.51 (3sf). I also used this for the time where it is travelling at the same speed for C and got t=0.609 (3sf). Will these still get me full marks??? Cheers
13. hey arsey,
1) thanks for the solutions !
2) in the last questions, if you dont round the Vvertical to 6, and leave it at 6.032, then you get a speed that rounds to 8.51 instead of 8.49 ( or something of that sort)... will they accept both?

apart from that, nice paper, and hopefully i got 100%
14. (Original post by Arsey)
to answer some questions....

asleep, I was asleep by 12:05!

Fine to leave in vector form; however, if you are ever unsure what it wants on a mecho paper, always do both! it would have been a crazy mark to lose.

units are not required

Boundaries will be sky high, it was 68 for an in June and this was waaaaay easier. Papers are meant to be checked and agreed to be of appropriate difficulty, this clearly slipped through the checking process. Other than COM where there were root 3s floating all over the place, it was stupidly easy.

we've never had 70 for an A, I just think it is a barrier they will not go to regardless of the results. I actually think setting a papers where they have had to make 69 an A last was a joke

so I think it will be 69 for an A and 72 for an A*
I agree with this. Obviously I wouldn't like a hard paper but very easy papers with ridiculous boundaries fails to effectively discriminate the a* candidates from the a grade candidates...1 silly mistake could make an a* disappear
15. (Original post by Phoebe x)
Arsey, for question 2c stupidly I must has written the pos vect out as the given vector when t is 4 equal to the integrated expresiion but for an unknown reason as I write the vector all in one like (not a column) I made it so that C is 0 plus 4i minus j so the pos vector was then the original intergrated answer plus 4i minus j..... Then subbed in 4 to get obvz a different answer..... Such a schoolboy error but as it was such an easy paper this queation could of cost me ! How many marks do you reckon I lost - all 5 or would I get any method marks as I simply got the wrong C value??

Thanks
Phoebe

I have read this about 3 times and I can not work out what you mean.

Integrating v = 2ti - 3t^2j to give s = t^2i - t^3j will be M1 A1 regardless of c

substituting in t = 1 (into your equation for a) and setting it equal to -4i + j will be M1

correctly working out s = (t^2 - 5)i + (2 - t^3)j will be A1

Subbing in t = 4 to give s = 11i - 62j will be A1

I doubt they will allow any follow through marks for the final two accuracy marks.

How many marks do you think you got?

This is the problem with the paper, it doesn't differentiate between the good and the very good students.
16. (Original post by Ibreiwish)
hey guys, I'd really appreciate a reply. The only mistake I made was in the 3b....a really stupid mistake. I don't know what the hell I was thinking...anyways what I did is that I took 75gsin5+20 as the resistance to motion, not remembering that I had already included the gain in p.e. and added to it the gain in p.e.

i equated 2400=(75gsin5+20+75gsin5)x and found the distance AB... how many marks do you think i would lose? i got the k.e. loss, and showed my reasoning behind equating k.e. loss to p.e. gain + work done against non gravitational resistive forces..but i added values in my working.

I did the exact same thing! Frustrating But the rest of the answers look familiar, so I hope I'll still be okay
17. This paper was lovely, after that awful chemistry F334 exam on thursday. Frankly that required harder maths than this Yey for 100%
18. (Original post by Arsey)
Phoebe

I have read this about 3 times and I can not work out what you mean.

Integrating v = 2ti - 3t^2j to give s = t^2i - t^3j will be M1 A1 regardless of c

substituting in t = 1 (into your equation for a) and setting it equal to -4i + j will be M1

correctly working out s = (t^2 - 5)i + (2 - t^3)j will be A1

Subbing in t = 4 to give s = 11i - 62j will be A1

I doubt they will allow any follow through marks for the final two accuracy marks.

How many marks do you think you got?

This is the problem with the paper, it doesn't differentiate between the good and the very good students.
Would you get penisalised for any 2 sf answers? For question 6)c) would you get all the marks for saying that the speed of C is 25u/36 because in part a) you worked out the speed is 5/6 the speed of the moving particle so it is (5/6)x(5u/6)?
I didn't write this and used the same method as you to make sure I got all the method marks.
19. (Original post by Ulgoo)
Would you get penisalised for any 2 sf answers? For question 6)c) would you get all the marks for saying that the speed of C is 25u/36 because in part a) you worked out the speed is 5/6 the speed of the moving particle so it is (5/6)x(5u/6)?
I didn't write this and used the same method as you to make sure I got all the method marks.
2sf will be fine on any question involving g

the second part of the collisions question is incredibly stupid, as you say it can be easily answered with no working.... I wouldn't have chanced it though.
20. (Original post by Arsey)
2sf will be fine on any question involving g

the second part of the collisions question is incredibly stupid, as you say it can be easily answered with no working.... I wouldn't have chanced it though.
What about 4)b) where I put 44 degrees because I've often seen it to the nearest degree in past papers?

Updated: May 29, 2012
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