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    (Original post by ombtom)
    Is there a thread for M4? If not, I'll make one.
    you might aswell make one since i can't find it tbh.
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    (Original post by physicsmaths)
    you might aswell make one since i can't find it tbh.
    On it! (I can't either.)
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    (Original post by physicsmaths)
    I always do the variable mass losing mass questions as m-deltam and other prticle as deltam. I always get the same answer, but the books says 'we always use m+deltam' why? And will i lose marks?
    dm/dt is generally taken to mean the rate of increase of m. In a rocket and fuel question, the mass is decreasing so dm/dt is negative. You are effectively taking dm/dt as the rate of decrease of mass. Mostly, provided that you are consistent, you will arrive at the same differential equation. Try June 2011. I think you will have a sign issue in that one.
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    (Original post by ombtom)
    I'm worried that I'm being too ambitious with M5; many people say that it's by far the hardest unit. So far I've only learnt M3, and I'm fine with it. I've also learnt FP2 and it's fine. Last year I taught myself AS Maths – I got over 90% – and this year I'm teaching myself AS and A2 Further Maths. I've applied for Physics at university. I am not doing STEP or anything like that.

    Based on this, do you think that I will be able to do well in M4/M5?
    no
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    (Original post by ApieceOFsoap)
    no
    :lol:

    It's not as hard as I was told.
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    I can't find the M4 thread so..

    Example of an unstable position of equilibrium:



    :rofl:
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    (Original post by Insight314)
    I can't find the M4 thread so..

    Example of an unstable position of equilibrium:



    :rofl:
    ombtom made one go on his profile and look under his threads it is there.


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    Do we need to specify in what way we're resolving and about which point we're taking the torques. I usually do, but let's say I forgot, would I lose marks?
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    Name:  Screen Shot 2016-05-30 at 23.44.24.png
Views: 130
Size:  50.0 KBAttachment 540903540905

    Before I boldly state that the mark scheme is wrong, why does it say that the moment of inertia of the particle is mx^2 and not 3mx^2?
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    In analysis of forces questions, when you get asked to show e.g that it is a couple and have to find cross-products of each force, is there a faster way than just setting up multiple determinants and working them out? That takes a long time, and it is very easy to make a mistake on.


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    (Original post by Insight314)
    In analysis of forces questions, when you get asked to show e.g that it is a couple and have to find cross-products of each force, is there a faster way than just setting up multiple determinants and working them out? That takes a long time, and it is very easy to make a mistake on.


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    I don't think there is... It's a pain in the a**

    Does it matter whether I evaluate the resultant moment as r x F or F x r? Of course, I get a negative answer to the mark scheme using F x r but otherwise?
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    (Original post by Euclidean)
    I don't think there is... It's a pain in the a**

    Does it matter whether I evaluate the resultant moment as r x F or F x r? Of course, I get a negative answer to the mark scheme using F x r but otherwise?
    It wouldn't if they require you to find the magnitude of the moment. If they don't, you need to make sure your direction is right. Also, you might get asked to find vector equation of direction of force that causes a moment which you would get wrong if you use it the other way around. It's pretty important to do it r x F.


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    (Original post by Insight314)
    It wouldn't if they require you to find the magnitude of the moment. If they don't, you need to make sure your direction is right. Also, you might get asked to find vector equation of direction of force that causes a moment which you would get wrong if you use it the other way around. It's pretty important to do it r x F.


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    Cheers. I've fixed my method now

    Anyone else quite worried about M5? I feel like I could easily be caught off guard with a tricky rotational dynamics question...

    Maybe I'm over thinking it :eek:

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    (Original post by Euclidean)
    Cheers. I've fixed my method now

    Anyone else quite worried about M5? I feel like I could easily be caught off guard with a tricky rotational dynamics question...

    Maybe I'm over thinking it :eek:
    This will be the year that they do something different with the variable mass question.
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    (Original post by ombtom)
    This will be the year that they do something different with the variable mass question.
    Well M3/4 have been rather straight forward with nothing really tricky so yeh, M5 gna be like ****ing step III mechanics.
    Forgive me lord, for he know not what he says. 😃🔫


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    (Original post by physicsmaths)
    Well M3/4 have been rather straight forward with nothing really tricky so yeh, M5 gna be like ****ing step III mechanics.
    Forgive me lord, for he know not what he says. 😃🔫
    We should stop worrying; last year there were 4 whole marks between A* and B. :lol:
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    (Original post by ombtom)
    This will be the year that they do something different with the variable mass question.
    I really like variable mass, infant the first half of the M5 specification is lovely. It's just that rotational rubbish that I can't ever seem to get right :lol:

    (Original post by physicsmaths)
    Well M3/4 have been rather straight forward with nothing really tricky so yeh, M5 gna be like ****ing step III mechanics.
    Forgive me lord, for he know not what he says. 😃🔫


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    lool

    (Original post by ombtom)
    We should stop worrying; last year there were 4 whole marks between A* and B. :lol:
    What was the A* boundary last year? I only have the A boundaries
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    (Original post by Euclidean)
    I really like variable mass, infant the first half of the M5 specification is lovely. It's just that rotational rubbish that I can't ever seem to get right :lol:



    lool



    What was the A* boundary last year? I only have the A boundaries
    Something like 71.


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    (Original post by Euclidean)
    What was the A* boundary last year? I only have the A boundaries
    71 A* (68 A).

    Maybe this will help you
    http://www.thestudentroom.co.uk/show....php?t=3917733
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    (Original post by ombtom)
    71 A* (68 A).

    Maybe this will help you
    http://www.thestudentroom.co.uk/show....php?t=3917733
    Times like this I wish there weren't rep restrictions. Thank you so much
 
 
 
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