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

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 :redface:

Reply 201

Yo12345

2

61/62 A* or high A?

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Reply 202

jjsnyder

OP

10

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 :redface:

The guy has a point. It was 11-6-X = 5-X iirc.

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Reply 203

IrrationalRoot

20

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 :redface:

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.

(edited 7 years ago)

Reply 204

steph-carys

14

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?

Reply 205

Hjyu1

2

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

Reply 206

steph-carys

14

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 :frown:

dont beat yourself up about it

Reply 207

Jm098

2

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

Reply 208

Hjyu1

2

Anyone doing grade boundary predictions ?

Reply 209

Yo12345

2

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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Reply 210

Jm098

2

I'd say 65 A*, 59 A etc

Reply 211

jjsnyder

OP

10

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 :frown:

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 :biggrin:

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(edited 7 years ago)

Reply 212

steph-carys

14

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 :biggrin:

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Ahahaha sounds like you've got it all covered! Not all of us are quite as lucky :wink:

Reply 213

iiPablo

1

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

Reply 214

LiesandAlibis

1

Do you guys think it'll be drop 2/3 marks for full UMS?

Reply 215

MilkFriend

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?

Reply 216

IrrationalRoot

20

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 :biggrin:

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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.