OCR Further Pure Core 2 2023 June — Question 10 7 marks

Exam BoardOCR
ModuleFurther Pure Core 2 (Further Pure Core 2)
Year2023
SessionJune
Marks7
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicPolar coordinates
TypeArea between two polar curves
DifficultyChallenging +1.2 This is a straightforward application of the polar area formula requiring students to find the area between two polar curves using integration. While it involves hyperbolic functions (cosh) and requires careful setup of the integral difference, the method is standard for Further Maths students. The final step of dividing by tin coverage and rounding up is routine. The question is slightly above average difficulty due to the Further Maths content and integration of cosh, but follows a predictable template without requiring novel insight.
Spec4.07a Hyperbolic definitions: sinh, cosh, tanh as exponentials4.09c Area enclosed: by polar curve

10 In this question you must show detailed reasoning. A region, \(R\), of the floor of an art gallery is to be painted for the purposes of an art installation. A suitable polar coordinate system is set up on the floor of the gallery with units in metres and radians. \(R\) is modelled as being the region enclosed by two curves, \(C _ { 1 }\) and \(C _ { 2 }\). The polar equations of \(C _ { 1 }\) and \(C _ { 2 }\) are $$\begin{array} { l l } C _ { 1 } : r = 5 , & - \frac { 1 } { 2 } \pi \leqslant \theta \leqslant \frac { 1 } { 2 } \pi \\ C _ { 2 } : r = 3 \cosh \theta , & - \frac { 1 } { 2 } \pi \leqslant \theta \leqslant \frac { 1 } { 2 } \pi \end{array}$$ Both curves are shown in the diagram, with \(R\) indicated. \includegraphics[max width=\textwidth, alt={}, center]{7b2bfb4e-524f-4d1c-ae98-075c7fb404f9-6_1481_821_836_251} The gallery must buy tins of paint to paint \(R\). Each tin of paint can cover an area of \(0.5 \mathrm {~m} ^ { 2 }\).
Determine the smallest number of tins of paint that the gallery must buy in order to be able to paint \(R\) completely.

Question 10:
AnswerMarks
10DR
C and C intersect when 1 2 5 3 c o s h  =
5 5
c o s h 1   = − so intersection at (  ) c o s h − 1 or
3 3
AnswerMarks Guidance
()ln3 or awrt ()1.10B1 3.1a
intersection of curves leading to
a correct expression or value for
an angle at a PoI
1 5
A 5 2 ( ) 2 5 ln 3 o r 2 5 c o s h 1   = − = − or
s e c to r 2 1
2 3
AnswerMarks Guidance
awrt 27.5B1ft 2.2a
of the sector (or half of it) either
using 1 r2 or 1   2(5)2 d .
2 2 
1
Accept lower limit of 0.
May be embedded in a
AnswerMarks
calculation for total area.5 5
Here c o s h 1 , c o s h 1   = − − = − or
1 2
3 3
( =−ln3 ),( =ln3 )
1 2
i.e. may later evaluate integral…
for some k
1 2 ( 3 c o s h ) 2 d o r 1 2 ( 3 c o s h ) 2 d        
2 2 0 
AnswerMarks Guidance
1M1 3.4
±their value for limits. Condone
AnswerMarks
lower limit of 05 5
Here c o s h 1 , c o s h 1   = − − = −
1 2
3 3
Limits can be seen later.
Later doubling may be seen
e e 2    + − 
c o s h 2 d d     =  =
2
1
e 2 e 2 2 d    =  + − +
AnswerMarks Guidance
4*M1 3.1a
into a form which can be
AnswerMarks
integrated.1
or cosh2d= 1+cosh2d
2
ln 3
e 2 e 2 2 d     + − +
ln 3 −
ln 3
1 1  
2 e e 2 2    = − − +
2 2
ln 3 −
1 1 1 1 1 1  
9 2 ln 3 9 2 ln 3 =  −  + −  −  −
2 2 9 2 9 2
8 0
4 ln 3 o r a w r t 1 3 .3 = +
AnswerMarks Guidance
9dep*M1 1.1
and substituting their limits.
Could be embedded.
NB
9 180  9
A =   +4ln3=10+ ln3
AnswerMarks
C2 2 4 9  2ln 3 ln 3
1
or c o s h 2 d 1 c o s h 2 d      =  +
2
ln 3 ln 3 − −
ln 3
1 1 2 0  
s in h 2 ln 3   = + = +
2 2 9
ln 3 −
 9  41
 trapped area =25ln3−10+ ln3= ln3−10
 2  2
AnswerMarks Guidance
or awrt 12.5 (12.521...)A1 1.1
both here and in the next line for
correct answers
12.52 / 0.5 = 25.04
AnswerMarks Guidance
so 26 tins of paint are neededA1 3.2a
[7]
PMT
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Question 10:
10 | DR
C and C intersect when 1 2 5 3 c o s h  =
5 5
c o s h 1   = − so intersection at (  ) c o s h − 1 or
3 3
()ln3 or awrt ()1.10 | B1 | 3.1a | Correct condition for
intersection of curves leading to
a correct expression or value for
an angle at a PoI
1 5
A 5 2 ( ) 2 5 ln 3 o r 2 5 c o s h 1   = − = − or
s e c to r 2 1
2 3
awrt 27.5 | B1ft | 2.2a | For finding (±) the correct area
of the sector (or half of it) either
using 1 r2 or 1   2(5)2 d .
2 2 
1
Accept lower limit of 0.
May be embedded in a
calculation for total area. | 5 5
Here c o s h 1 , c o s h 1   = − − = − or
1 2
3 3
( =−ln3 ),( =ln3 )
1 2
i.e. may later evaluate integral…
for some k
1 2 ( 3 c o s h ) 2 d o r 1 2 ( 3 c o s h ) 2 d        
2 2 0 
1 | M1 | 3.4 | Correct use of area formula with
±their value for limits. Condone
lower limit of 0 | 5 5
Here c o s h 1 , c o s h 1   = − − = −
1 2
3 3
Limits can be seen later.
Later doubling may be seen
e e 2    + − 
c o s h 2 d d     =  =
2
1
e 2 e 2 2 d    =  + − +
4 | *M1 | 3.1a | Correct conversion of cosh2
into a form which can be
integrated. | 1
or cosh2d= 1+cosh2d
2
ln 3
e 2 e 2 2 d     + − +
ln 3 −
ln 3
1 1  
2 e e 2 2    = − − +
2 2
ln 3 −
1 1 1 1 1 1  
9 2 ln 3 9 2 ln 3 =  −  + −  −  −
2 2 9 2 9 2
8 0
4 ln 3 o r a w r t 1 3 .3 = +
9 | dep*M1 | 1.1 | Correctly integrating cosh2
and substituting their limits.
Could be embedded.
NB
9 180  9
A =   +4ln3=10+ ln3
C2 2 4 9  2 | ln 3 ln 3
1
or c o s h 2 d 1 c o s h 2 d      =  +
2
ln 3 ln 3 − −
ln 3
1 1 2 0  
s in h 2 ln 3   = + = +
2 2 9
ln 3 −
 9  41
 trapped area =25ln3−10+ ln3= ln3−10
 2  2
or awrt 12.5 (12.521...) | A1 | 1.1 | Accept unsimplified form | If B1B1M1M0M0 can score ScB1
both here and in the next line for
correct answers
12.52 / 0.5 = 25.04
so 26 tins of paint are needed | A1 | 3.2a
[7]
PMT
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OCR is part of Cambridge University Press & Assessment, a department of the University of Cambridge.
For staff training purposes and as part of our quality assurance programme your call may be recorded or monitored. © OCR
2023 Oxford Cambridge and RSA Examinations is a Company Limited by Guarantee. Registered in England. Registered office
The Triangle Building, Shaftesbury Road, Cambridge, CB2 8EA.
Registered company number 3484466. OCR is an exempt charity.
OCR operates academic and vocational qualifications regulated by Ofqual, Qualifications Wales and CCEA as listed in their
qualifications registers including A Levels, GCSEs, Cambridge Technicals and Cambridge Nationals.
OCR provides resources to help you deliver our qualifications. These resources do not represent any particular teaching method
we expect you to use. We update our resources regularly and aim to make sure content is accurate but please check the OCR
website so that you have the most up-to-date version. OCR cannot be held responsible for any errors or omissions in these
resources.
Though we make every effort to check our resources, there may be contradictions between published support and the
specification, so it is important that you always use information in the latest specification. We indicate any specification changes
within the document itself, change the version number and provide a summary of the changes. If you do notice a discrepancy
between the specification and a resource, please contact us.
Whether you already offer OCR qualifications, are new to OCR or are thinking about switching, you can request more
information using our Expression of Interest form.
Please get in touch if you want to discuss the accessibility of resources we offer to support you in delivering our qualifications.
10 In this question you must show detailed reasoning.
A region, $R$, of the floor of an art gallery is to be painted for the purposes of an art installation. A suitable polar coordinate system is set up on the floor of the gallery with units in metres and radians. $R$ is modelled as being the region enclosed by two curves, $C _ { 1 }$ and $C _ { 2 }$. The polar equations of $C _ { 1 }$ and $C _ { 2 }$ are

$$\begin{array} { l l } 
C _ { 1 } : r = 5 , & - \frac { 1 } { 2 } \pi \leqslant \theta \leqslant \frac { 1 } { 2 } \pi \\
C _ { 2 } : r = 3 \cosh \theta , & - \frac { 1 } { 2 } \pi \leqslant \theta \leqslant \frac { 1 } { 2 } \pi
\end{array}$$

Both curves are shown in the diagram, with $R$ indicated.\\
\includegraphics[max width=\textwidth, alt={}, center]{7b2bfb4e-524f-4d1c-ae98-075c7fb404f9-6_1481_821_836_251}

The gallery must buy tins of paint to paint $R$. Each tin of paint can cover an area of $0.5 \mathrm {~m} ^ { 2 }$.\\
Determine the smallest number of tins of paint that the gallery must buy in order to be able to paint $R$ completely.

\hfill \mbox{\textit{OCR Further Pure Core 2 2023 Q10 [7]}}