CCEA C4 Mathematics - 22nd May 2014 Watch

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stephen_mcgarry
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#101
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#101
(Original post by dylaaaan)
For Q5 (the differential equation) how many marks would you loose, if any, for writing down the wrong time but getting the correct answer? i wrote 07:28 am :ahhhhh: ..and the last question i did everything correct getting -45, but put it into the CAST digram wrong and got t=3/4pi(135) would i just loose the one mark or?
I did that as well :/ forgot it was negative so would go in the opposite quadrants hopefully not loose too many marks

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GingerCodeMan
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#102
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#102
(Original post by Son1809)
With respect to 4ii), flat bottom isn't a modelling assumption - the curve gives a flat bottom as it is. I think the assumption was that the bowl's walls took up no volume, or that thickness had a negligible effect on volume, or something.
I agree. I've heard so many people say that the assumption was 'flat base' or something similar ... but the volume is already a flat base, so I can't see how that can be right. I think most people thought it was this because of a past paper that had a fish bowl, and you had to state a criticism of the model, which was that the model didn't have a flat base.

I also said that the surface didn't take up any of the volume of the bowl/negligible thickness ...
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crazers
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#103
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#103
(Original post by Son1809)
With respect to 4ii), flat bottom isn't a modelling assumption - the curve gives a flat bottom as it is. I think the assumption was that the bowl's walls took up no volume, or that thickness had a negligible effect on volume, or something.
I think the assumption that the bottom is not flat is correct. In other words if it had a flat bottom rotating about the x axis would give the volume, bar the central column above the base. The answer is given as that in may 2011 as you can see below. The question was asking what was the flaw in the rotating method.Name:  ImageUploadedByStudent Room1401021304.190796.jpg
Views: 62
Size:  36.1 KB


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GingerCodeMan
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#104
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#104
(Original post by crazers)
I think the assumption that the bottom is not flat is correct. In other words if it had a flat bottom rotating about the x axis would give the volume, bar the central column above the base. The answer is given as that in may 2011 as you can see below. The question was asking what was the flaw in the rotating method.Name:  ImageUploadedByStudent Room1401021304.190796.jpg
Views: 62
Size:  36.1 KB


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The May 2011 question was referring to the surface of a fish bowl which was modelled by part of the curve \sqrt{144-x^2}, which looks like this:
Name:  Fish_Bowl_Question.jpg
Views: 63
Size:  9.2 KB

We know that a fish bowl needs to have a flat base, but the curve upon which the surface is modelled would not have a flat base if rotated between the specified limits, so we can say the criticism of the model is "The bowl needs a flat bottom"/"The model does not represent a bowl with a flat bottom".

For this year's paper, I drew a sketch of the curve in the exam to confirm that it would already have a flat base, so we do not have to make the assumption that it has a flat base. This is what the curve looks like between x = 0 and x = 1:
Name:  Glass Bowl.PNG
Views: 66
Size:  3.8 KB
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RainbowVeins
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#105
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#105
(Original post by GingerCodeMan)
The May 2011 question was referring to the surface of a fish bowl which was modelled by part of the curve \sqrt{144-x^2}, which looks like this:
Name:  Fish_Bowl_Question.jpg
Views: 63
Size:  9.2 KB

We know that a fish bowl needs to have a flat base, but the curve upon which the surface is modelled would not have a flat base if rotated between the specified limits, so we can say the criticism of the model is "The bowl needs a flat bottom"/"The model does not represent a bowl with a flat bottom".

For this year's paper, I drew a sketch of the curve in the exam to confirm that it would already have a flat base, so we do not have to make the assumption that it has a flat base. This is what the curve looks like between x = 0 and x = 1:
Name:  Glass Bowl.PNG
Views: 66
Size:  3.8 KB
In the exam I was thinking there might be bowls without a flat base...like those bases that are slightly curved up. I have way too much imagination it hurts

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stephen_mcgarry
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#106
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#106
Oh also can I ask, if like I said, I were to get 65+/75 in both C3 and C4 would this be likely to be enough for an A*? I know I need 480/600, but I should get that OK, was just wondering about the 90% average

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