OCR MEI Further Mechanics A AS 2024 June — Question 6 10 marks

Exam BoardOCR MEI
ModuleFurther Mechanics A AS (Further Mechanics A AS)
Year2024
SessionJune
Marks10
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicCentre of Mass 1
TypeSuspended lamina equilibrium angle
DifficultyStandard +0.8 This is a multi-part centre of mass problem requiring: (a) finding the centroid of a trapezium using coordinate geometry/integration or decomposition, (b) applying equilibrium conditions when suspended (vertical line through support must pass through centre of mass), and (c) using trigonometry with the equilibrium angle. While the individual techniques are standard for Further Mechanics, the combination of algebraic manipulation with parameters p and q, geometric reasoning about equilibrium orientations, and the multi-step nature makes this moderately challenging—above average difficulty but not requiring exceptional insight.
Spec6.04b Find centre of mass: using symmetry6.04c Composite bodies: centre of mass

6 A uniform lamina OABC is in the shape of a trapezium where O is the origin of the coordinate system in which the points \(A , B\) and \(C\) have coordinates \(( 12,0 ) , ( 12 + p , q )\) and \(( 0 , q )\) respectively. \includegraphics[max width=\textwidth, alt={}, center]{a96a0ebe-8f4f-4d79-9d11-9d348ef72314-7_536_917_349_239}
  1. Determine, in terms of \(p\) and \(q\), the coordinates of the centre of mass of OABC . The point D has coordinates \(( 7.6 , q )\). When OABC is suspended from D , the lamina hangs in equilibrium with BC horizontal.
  2. Determine the value of \(p\). When OABC is suspended from C, the lamina hangs in equilibrium with BC at an angle of \(35 ^ { \circ }\) to the downward vertical.
  3. Determine the value of \(q\), giving your answer correct to \(\mathbf { 3 }\) significant figures.

Question 6:
AnswerMarks Guidance
6(a) ( )
Area= 12q+1 pq
2
x  6  12+1 p
( 12q+1 2 pq )  y   =12q  1 2 q   +1 2 pq   3 2q 3   
72+6p+1 p2  432+36p+ p2 
x = 6 = 
 
12+ 1 p  72+3p 
2
6q+1 pq  36q+2pq
 y = 3 = 
12+1 p  72+3p 
AnswerMarks
2B1
M1
A1
A1
AnswerMarks
[4]1.1
3.3
1.1
AnswerMarks
1.1soi Award if correct ratios 24 : p : (24+p) oe used
Equation for one component Allow one error
Count 𝑥̅ and 𝑦̅ interchanged as one error
Equation for one component correct FT their area
Condone missing brackets if the intention is clear
This M1A1 can be awarded for a frame (see below)
cao Both components (any correct form)
SC Considered as a uniform frame (Max 2/4)
1
𝑥̅ 6 12+ 𝑝 6+ 1 𝑝 0
(24+𝑝+𝑞+√𝑝2+𝑞2 )( ) = (12)( )+√𝑝2+𝑞2( 2 )+(12+𝑝)( 2 )+𝑞(1 )
𝑦̅ 0 1 𝑞 𝑞 𝑞
2
AnswerMarks
21
𝑥̅ 6 12+ 𝑝 6+ 1 𝑝 0
(24+𝑝+𝑞+√𝑝2+𝑞2 )( ) = (12)( )+√𝑝2+𝑞2( 2 )+(12+𝑝)( 2 )+𝑞(1 )
𝑦̅ 0 1 𝑞 𝑞 𝑞
2
AnswerMarks
2M1 Equation for one component Allow one error
A1 Equation for one component correctM1 Equation for one component Allow one error
A1 Equation for one component correct
AnswerMarks
(b)x =7.6
432+36p+ p2 =7.6(72+3p)
 p2 +13.2p−115.2=0
AnswerMarks
 p=6B1
M1
A1
AnswerMarks
[3]3.1b
1.1
AnswerMarks
1.1Stated or implied, e.g. by equating their expression
for 𝑥̅ in part (a) to 7.6. Ignore incorrect value of y ,
e.g. ‘(7.6, q) is the CM’ earns B1
Equating their expression for 𝑥̅ in part (a) to 7.6, and
obtaining a three term quadratic equation for p
(Not necessarily …=0) Implied by 𝑝 = 6 www
BC
AnswerMarks
(c)6q+16q
y = 3 ( = 81 q )
12+16 5
2
𝑞−𝑦̅ = 7.6tan35° (= 5.32)
AnswerMarks
𝑞 = 11.4M1
M1
A1
AnswerMarks
[3]3.4
3.1b
AnswerMarks
1.1Substituting their p into their expression for y
M0 if their y does not contain p
soi Allow 7.6/tan35° or equivalent
If their 𝑦̅ = ½𝑞, then ½𝑞 = 5.32, by itself, is M0
Allow 30° as a misread for 35°
Awrt 11.4 (11.403379…)
PMT
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Question 6:
6 | (a) | ( )
Area= 12q+1 pq
2
x  6  12+1 p
( 12q+1 2 pq )  y   =12q  1 2 q   +1 2 pq   3 2q 3   
72+6p+1 p2  432+36p+ p2 
x = 6 = 
 
12+ 1 p  72+3p 
2
6q+1 pq  36q+2pq
 y = 3 = 
12+1 p  72+3p 
2 | B1
M1
A1
A1
[4] | 1.1
3.3
1.1
1.1 | soi Award if correct ratios 24 : p : (24+p) oe used
Equation for one component Allow one error
Count 𝑥̅ and 𝑦̅ interchanged as one error
Equation for one component correct FT their area
Condone missing brackets if the intention is clear
This M1A1 can be awarded for a frame (see below)
cao Both components (any correct form)
SC Considered as a uniform frame (Max 2/4)
1
𝑥̅ 6 12+ 𝑝 6+ 1 𝑝 0
(24+𝑝+𝑞+√𝑝2+𝑞2 )( ) = (12)( )+√𝑝2+𝑞2( 2 )+(12+𝑝)( 2 )+𝑞(1 )
𝑦̅ 0 1 𝑞 𝑞 𝑞
2
2 | 1
𝑥̅ 6 12+ 𝑝 6+ 1 𝑝 0
(24+𝑝+𝑞+√𝑝2+𝑞2 )( ) = (12)( )+√𝑝2+𝑞2( 2 )+(12+𝑝)( 2 )+𝑞(1 )
𝑦̅ 0 1 𝑞 𝑞 𝑞
2
2 | M1 Equation for one component Allow one error
A1 Equation for one component correct | M1 Equation for one component Allow one error
A1 Equation for one component correct
(b) | x =7.6
432+36p+ p2 =7.6(72+3p)
 p2 +13.2p−115.2=0
 p=6 | B1
M1
A1
[3] | 3.1b
1.1
1.1 | Stated or implied, e.g. by equating their expression
for 𝑥̅ in part (a) to 7.6. Ignore incorrect value of y ,
e.g. ‘(7.6, q) is the CM’ earns B1
Equating their expression for 𝑥̅ in part (a) to 7.6, and
obtaining a three term quadratic equation for p
(Not necessarily …=0) Implied by 𝑝 = 6 www
BC
(c) | 6q+16q
y = 3 ( = 81 q )
12+16 5
2
𝑞−𝑦̅ = 7.6tan35° (= 5.32)
𝑞 = 11.4 | M1
M1
A1
[3] | 3.4
3.1b
1.1 | Substituting their p into their expression for y
M0 if their y does not contain p
soi Allow 7.6/tan35° or equivalent
If their 𝑦̅ = ½𝑞, then ½𝑞 = 5.32, by itself, is M0
Allow 30° as a misread for 35°
Awrt 11.4 (11.403379…)
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
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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
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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.
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Please get in touch if you want to discuss the accessibility of resources we offer to support you in delivering our qualifications.
6 A uniform lamina OABC is in the shape of a trapezium where O is the origin of the coordinate system in which the points $A , B$ and $C$ have coordinates $( 12,0 ) , ( 12 + p , q )$ and $( 0 , q )$ respectively.\\
\includegraphics[max width=\textwidth, alt={}, center]{a96a0ebe-8f4f-4d79-9d11-9d348ef72314-7_536_917_349_239}
\begin{enumerate}[label=(\alph*)]
\item Determine, in terms of $p$ and $q$, the coordinates of the centre of mass of OABC .

The point D has coordinates $( 7.6 , q )$. When OABC is suspended from D , the lamina hangs in equilibrium with BC horizontal.
\item Determine the value of $p$.

When OABC is suspended from C, the lamina hangs in equilibrium with BC at an angle of $35 ^ { \circ }$ to the downward vertical.
\item Determine the value of $q$, giving your answer correct to $\mathbf { 3 }$ significant figures.
\end{enumerate}

\hfill \mbox{\textit{OCR MEI Further Mechanics A AS 2024 Q6 [10]}}