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Date May 2017 Marks available 5 Reference code 17M.1.SL.TZ2.S_9
Level Standard Level Paper Paper 1 (without calculator) Time zone Time zone 2
Command term Find Question number S_9 Adapted from N/A

Question

Note: In this question, distance is in metres and time is in seconds.

Two particles P1P1 and P2P2 start moving from a point A at the same time, along different straight lines.

After tt seconds, the position of P1P1 is given by r = (413)+t(121)413+t121.

Two seconds after leaving A, P1P1 is at point B.

Two seconds after leaving A, P2P2 is at point C, where AC=(304)AC=304.

Find the coordinates of A.

[2]
a.

Find ABAB;

[3]
b.i.

Find |AB|AB.

[2]
b.ii.

Find cosBˆACcosB^AC.

[5]
c.

Hence or otherwise, find the distance between P1P1 and P2P2 two seconds after they leave A.

[4]
d.

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

recognizing t=0t=0 at A     (M1)

A is (4, 1, 3)(4, 1, 3)     A1     N2

[2 marks]

a.

METHOD 1

valid approach     (M1)

eg(413)+2(122), (6, 3, 1)413+2122, (6, 3, 1)

correct approach to find ABAB     (A1)

egAO+OB, BA, (631)(413)AO+OB, BA, 631413

AB=(244)AB=244     A1     N2

METHOD 2

recognizing ABAB is two times the direction vector     (M1)

correct working     (A1)

egAB=2(122)AB=2122

AB=(244)AB=244     A1     N2

[3 marks]

b.i.

correct substitution     (A1)

eg|AB|=22+42+42, 4+16+16, 36AB=22+42+42, 4+16+16, 36

|AB|=6AB=6     A1     N2

[2 marks]

b.ii.

METHOD 1 (vector approach)

valid approach involving ABAB and ACAC     (M1)

egABAC, BAACAB×ACABAC, BAACAB×AC

finding scalar product and |AC|AC     (A1)(A1)

scalar product 2(3)+4(0)4(4) (=10)2(3)+4(0)4(4) (=10)

|AC|=32+02+42 (=5)AC=32+02+42 (=5)

substitution of their scalar product and magnitudes into cosine formula     (M1)

egcosBˆAC=6+016632+42cosB^AC=6+016632+42

cosBˆAC=1030(=13)cosB^AC=1030(=13)     A1     N2

 

METHOD 2 (triangle approach)

valid approach involving cosine rule     (M1)

egcosBˆAC=AB2+AC2BC22×AB×ACcosB^AC=AB2+AC2BC22×AB×AC

finding lengths AC and BC     (A1)(A1)

AC=5, BC=9AC=5, BC=9

substitution of their lengths into cosine formula     (M1)

egcosBˆAC=52+62922×5×6cosB^AC=52+62922×5×6

cosBˆAC=2060 (=13)cosB^AC=2060 (=13)     A1     N2

[5 marks]

c.

Note:     Award relevant marks for working seen to find BC in part (c) (if cosine rule used in part (c)).

 

METHOD 1 (using cosine rule)

recognizing need to find BC     (M1)

choosing cosine rule     (M1)

egc2=a2+b22abcosCc2=a2+b22abcosC

correct substitution into RHS     A1

egBC2=(6)2+(5)22(6)(5)(13), 36+25+20BC2=(6)2+(5)22(6)(5)(13), 36+25+20

distance is 9     A1     N2

 

METHOD 2 (finding magnitude of BCBC

recognizing need to find BC     (M1)

valid approach     (M1)

egattempt to find OBOB or OCOC, OB=(631)OB=631 or OC=(717), BA+ACOC=717, BA+AC

correct working     A1

egBC=(148), CB=(148), 12+42+82=81BC=148, CB=148, 12+42+82=81

distance is 9     A1     N2

 

METHOD 3 (finding coordinates and using distance formula)

recognizing need to find BC     (M1)

valid approach     (M1)

egattempt to find coordinates of B or C, B(6, 3, 1)B(6, 3, 1) or C(7, 1, 7)C(7, 1, 7)

correct substitution into distance formula     A1

egBC=(67)2+(3(1))2+(17)2, 12+42+82=81BC=(67)2+(3(1))2+(17)2, 12+42+82=81

distance is 9     A1     N2

[4 marks]

d.

Examiners report

[N/A]
a.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
c.
[N/A]
d.

Syllabus sections

Topic 3— Geometry and trigonometry » AHL 3.14—Vector equation of line
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Topic 3— Geometry and trigonometry

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