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# AQA A2 Mathematics MM2B Mechanics 2 - Monday 22nd June 2015 [Exam Discussion Thread] watch

1. (Original post by ellie--may)
How can we tell if the string is taut or slack when it comes to rest for the first time? In the mark scheme it has EPE when it comes to rest so i can see this means it is still taut, but why?
I think it is to do with the weight of the particle attached. The tension in the string and the weight are in equilibrium I think.
2. (Original post by Stepidermis)
This is just the one module that I can't do! I always miss things when doing questions or make stupid mistakes and then I can't deal with the outside of the box questions... I think it just hasn't clicked for me which is fine since I can do every other module, this just gives me brain veins
Aha. Everyone has their weak modules dw. I can only really do M2 because of Physics!

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3. (Original post by Reverse Swing)
I think it is to do with the weight of the particle attached. The tension in the string and the weight are in equilibrium I think.
But equilibrium does not necessarily mean at rest? For the particle to begin slowing down in order to be at rest there must be deceleration occurring due to a net/resultant downward force, where the Weight component is greater than the tension in the string.
4. (Original post by CD223)
Haha, we all know the feeling buddy - so tired after all these exams

Anyway, that's correct

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Haha yeah ah well, this is exam 7 of 8 so nearly there I guess! Thanks for that

Tired me again! xD This time I'm driving myself insane over a hooke's law/work-energy principle question from the textbook.... I got v=4.8ms^-1 but the answer says it's 2.52ms^-1...

Would be really grateful if anyone can help me figure out what I did wrong :P Really sorry for the horrendous pic quality aha, not a great camera I know :/ I'm just trying to cram a bit and get some work done before the exam tomorrow (sorry i had to!)
Attachment 433409433411
Attached Images

5. (Original post by tripleseven)
Haha yeah ah well, this is exam 7 of 8 so nearly there I guess! Thanks for that

Tired me again! xD This time I'm driving myself insane over a hooke's law/work-energy principle question from the textbook.... I got v=4.8ms^-1 but the answer says it's 2.52ms^-1...

Would be really grateful if anyone can help me figure out what I did wrong :P Really sorry for the horrendous pic quality aha, not a great camera I know :/ I'm just trying to cram a bit and get some work done before the exam tomorrow (sorry i had to!)
Attachment 433409433411
Hey, you don't have to work out the work done by tension.

There's a loss in EPE of 2.5
There's a gain in KE of 0.3v^2
The work done by friction is 0.588

Therefore 2.5 = 0.3v^2 + 0.588
Which leads to v = 2.52ms^-1
6. (Original post by JustRiseAgainst)
Hey, you don't have to work out the work done by tension.

There's a loss in EPE of 2.5
There's a gain in KE of 0.3v^2
The work done by friction is 0.588

Therefore 2.5 = 0.3v^2 + 0.588
Which leads to v = 2.52ms^-1
Ah I see... why would that be then? Sorry for my ignorance aha, I get quite confused about those kinda things - when is it necessary to work out the work done by tension? I also get confused by which way round to do Gain in KE - Loss in EPE or Loss in EPE - Gain in KE...
7. If anyone has the Heinemann M2 AQA book, could someone explain Exercise 6A Question 5? I get 117, when the answer is apparently 110...
8. (Original post by ellie--may)
But equilibrium does not necessarily mean at rest? For the particle to begin slowing down in order to be at rest there must be deceleration occurring due to a net/resultant downward force, where the Weight component is greater than the tension in the string.
I'm not entirely sure to be honest. I just assume that it is taut.

Also as far as I know there is a resultant downward force due to the weight however as the string begins to stretch the tension in the string also increases, while the weight stays constant. Eventually tension = weight, and that is when you get equilibrium.

It would be best if someone else answers this question.
9. So the majority of those who do M2 do it as an applied module for Further Maths?
10. (Original post by Tiwa)
So the majority of those who do M2 do it as an applied module for Further Maths?
thats what i do
11. (Original post by CD223)
Aha. Everyone has their weak modules dw. I can only really do M2 because of Physics!

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Lucky you, I knew i should have picked physics..

12. 6b(ii) anyone? Answer is 23mg/30 and its from an old past paper and I can't understand how to do it???
13. (Original post by Tiwa)
So the majority of those who do M2 do it as an applied module for Further Maths?
Not really, no one in my mechanics class does further maths, but 90% of them do physics,, apart from me.. *sigh*
14. Can anybody tell me the method for working out centre of mass of a body where it has a shape cut out of it? Thanks
15. This may be a stupid question, but on questions like June 14 8(b) and June 13 9(c), how come we use the work done against friction and not the overall work done by the resultant force on the object?
16. (Original post by JackNorman)
Can anybody tell me the method for working out centre of mass of a body where it has a shape cut out of it? Thanks
Usually if dealing with areas you take away the area of the shape cut out of lamina when calculating the total mass, but still include its centre of mass in calculations, instead subtracting rather than adding the individual masses.

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17. Good luck everyone! you'll be fine.

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18. (Original post by CD223)
Good luck everyone! you'll be fine.

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The same to you. Thanks man!
19. All the best everyone. God bless.
20. Will be on to discuss the paper afterwards. Good luck.

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