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Date May 2017 Marks available 2 Reference code 17M.2.SL.TZ1.S_8
Level Standard Level Paper Paper 2 Time zone Time zone 1
Command term Question number S_8 Adapted from N/A

Question

At Grande Anse Beach the height of the water in metres is modelled by the function h ( t ) = p cos ( q × t ) + r , where t is the number of hours after 21:00 hours on 10 December 2017. The following diagram shows the graph of h , for 0 t 72 .

M17/5/MATME/SP2/ENG/TZ1/08

The point A ( 6.25 ,   0.6 ) represents the first low tide and B ( 12.5 ,   1.5 ) represents the next high tide.

How much time is there between the first low tide and the next high tide?

[2]
a.i.

Find the difference in height between low tide and high tide.

[2]
a.ii.

Find the value of p ;

[2]
b.i.

Find the value of q ;

[3]
b.ii.

Find the value of r .

[2]
b.iii.

There are two high tides on 12 December 2017. At what time does the second high tide occur?

[3]
c.

Markscheme

attempt to find the difference of x -values of A and B     (M1)

eg 6.25 12.5  

6.25 (hours), (6 hours 15 minutes)     A1     N2

[2 marks]

a.i.

attempt to find the difference of y -values of A and B     (M1)

eg 1.5 0.6

0.9  (m)     A1     N2

[2 marks]

a.ii.

valid approach     (M1)

eg max min 2 ,   0.9 ÷ 2

p = 0.45     A1     N2

[2 marks]

b.i.

METHOD 1

period = 12.5 (seen anywhere)     (A1)

valid approach (seen anywhere)     (M1)

eg period = 2 π b ,   q = 2 π period ,   2 π 12.5

0.502654

q = 4 π 25 ,  0.503  ( or  4 π 25 ,   0.503 )     A1     N2

METHOD 2

attempt to use a coordinate to make an equation     (M1)

eg p cos ( 6.25 q ) + r = 0.6 ,   p cos ( 12.5 q ) + r = 1.5

correct substitution     (A1)

eg 0.45 cos ( 6.25 q ) + 1.05 = 0.6 ,   0.45 cos ( 12.5 q ) + 1.05 = 1.5

0.502654

q = 4 π 25 ,   0.503   ( or  4 π 25 ,   0.503 )     A1     N2

[3 marks]

b.ii.

valid method to find r     (M1)

eg max + min 2 ,   0.6 + 0.45

r = 1.05     A1     N2

[2 marks]

b.iii.

METHOD 1

attempt to find start or end t -values for 12 December     (M1)

eg 3 + 24 ,   t = 27 ,   t = 51

finds t -value for second max     (A1)

t = 50

23:00 (or 11 pm)     A1     N3

METHOD 2 

valid approach to list either the times of high tides after 21:00 or the t -values of high tides after 21:00, showing at least two times     (M1) 

eg 21:00 + 12.5 ,  21:00 + 25 ,   12.5 + 12.5 ,   25 + 12.5

correct time of first high tide on 12 December     (A1)

eg 10:30 (or 10:30 am) 

time of second high tide = 23:00     A1     N3

METHOD 3

attempt to set their h equal to 1.5     (M1)

eg h ( t ) = 1.5 ,   0.45 cos ( 4 π 25 t ) + 1.05 = 1.5

correct working to find second max     (A1)

eg 0.503 t = 8 π ,   t = 50

23:00 (or 11 pm)     A1     N3

[3 marks]

c.

Examiners report

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

Syllabus sections

Topic 2—Functions » SL 2.5—Modelling functions
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