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AQA A2 MM2B Mechanics 2 – 27th June 2016 [Exam Discussion Thread] Watch

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    (Original post by IrrationalRoot)
    Is this the method that anyone else used for Q8? Not sure where I went wrong.

    No KEs to consider first of all. Now by conservation of energy,

    GPE+EPE before = GPE+EPE+Work after

    Taking x to be the distance from A when next at rest, height for GPE is x/2. (xsin30.)
    This is taking the 0 GPE level to be at the point when next at rest.

    EPE is for one string, since extension 0 for one string, extension 5 for the other so EPE from that string.

    Because of our choice of GPE level, GPE=0 after.

    EPE after is total of the two EPEs for both strings, so with extension of x in one of them and extension of x-6 in another.

    Work found by x multiplied by coefficient of friction multiplied by reaction force which is mgcos30.

    Then I got two answers, chose the larger one, added 4 (got 7.05m).
    I'm confused with why you put x-6 as being e for one string, I put x as extension for top string and (5-x) for the remaining extension of the bottom string as the mass moves downwards
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    61/62 A* or high A?


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    (Original post by steph-carys)
    I'm confused with why you put x-6 as being e for one string, I put x as extension for top string and (5-x) for the remaining extension of the bottom string as the mass moves downwards
    The guy has a point. It was 11-6-X = 5-X iirc.


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    (Original post by steph-carys)
    I'm confused with why you put x-6 as being e for one string, I put x as extension for top string and (5-x) for the remaining extension of the bottom string as the mass moves downwards
    Wouldn't the extension be the distance P travels beyond the string's natural length (6) so that it would be x-6? Might be wrong though.

    EDIT: Nvm, I'm an idiot. Probably lost another 7 marks or something, what a terrible performance.
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    Damnnn I've worked out what I did wrong on question 8... put my GPE on the wrong bloody side! Hopefully won't lose too many marks for that?
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    (Original post by Yo12345)
    61/62 A* or high A?


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    I'm hoping it's like that but a lot of people have seem to have done alright
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    (Original post by IrrationalRoot)
    Wouldn't the extension be the distance P travels beyond the string's natural length (6) so that it would be x-6? Might be wrong though.

    EDIT: Nvm, I'm an idiot. Probably lost another 7 marks or something, what a terrible performance.
    It's okay dude, I'm sure you'll still get a bunch of method marks, I made some stupid mistakes too dont beat yourself up about it
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    (Original post by IrrationalRoot)
    Wouldn't the extension be the distance P travels beyond the string's natural length (6) so t it would be x-6? Might be wrong though.

    EDIT: Nvm, I'm an idiot. Probably lost another 7 marks or something, what a terrible performance.
    i put 5-X. I can see your thinking but I can explain why that's wrong. I think it's the way you do it, because if it's X-6 you're implying that the extension would be greater than the original extension which was 5. Idk haha
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    Anyone doing grade boundary predictions ?
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    (Original post by Jm098)
    i put 5-X. I can see your thinking but I can explain why that's wrong. I think it's the way you do it, because if it's X-6 you're implying that the extension would be greater than the original extension which was 5. Idk haha
    I put 5 + x. Probably wrong


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    I'd say 65 A*, 59 A etc
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    (Original post by steph-carys)
    It's okay dude, I'm sure you'll still get a bunch of method marks, I made some stupid mistakes too dont beat yourself up about it
    I haven't really revised this module at all and so didn't know Work done = Fscos(theta) :P therefore didn't do the cos30 on the friction.
    EDIT: Needed 0UMS, think I should just about be fine

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    (Original post by jjsnyder)
    I haven't really revised this module at all and so didn't know Work done = Fscos(theta) :P therefore didn't do the cos30 on the friction.
    EDIT: Needed 0UMS, think I should just about be fine

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    Ahahaha sounds like you've got it all covered! Not all of us are quite as lucky
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    (Original post by C0balt)
    Well I wholeheartedly hope you are right. I honestly think 2015 was more difficult overall but I can hope.
    I think the fact that it featured questions similar to recent year's will probably mean standard grade boundaries as lots of students will have recognised the questions and been confident in them, I.e. The differential question, which I personally only got right bc I'd seen it in a previous year.
    However, the fact that last year had that incredibly easy 9 marker might have increased the boundaries so maybe they'll be slightly lower, we can live in hope ay
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    Do you guys think it'll be drop 2/3 marks for full UMS?
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    So didn't notice theres friction acting on the last question until I walked out of the room... didn't consider friction at all but done the EPE and GPE parts right. How many marks am I likely to lose guys?
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    (Original post by jjsnyder)
    I haven't really revised this module at all and so didn't know Work done = Fscos(theta) :P therefore didn't do the cos30 on the friction.
    EDIT: Needed 0UMS, think I should just about be fine

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    I needed 0UMS too XD. Still really disappointing that I got 80s in this paper, worst mark I've got in an M2 paper by far and that's just from two tiny mistakes.
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    Also, is there a general consensus on 2(root)gl versus (root)5gl?
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    (Original post by LiesandAlibis)
    Do you guys think it'll be drop 2/3 marks for full UMS?
    Yeah, maximum 5 I reckon, if we're lucky.
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    (Original post by LiesandAlibis)
    Also, is there a general consensus on 2(root)gl versus (root)5gl?
    Yes there is the correct answer is \sqrt{5gl} and that is certain.
 
 
 
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