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Date May 2022 Marks available 1 Reference code 22M.2.SL.TZ1.1
Level Standard Level Paper Paper 2 Time zone Time zone 1
Command term Write down Question number 1 Adapted from N/A

Question

Boris recorded the number of daylight hours on the first day of each month in a northern hemisphere town.

This data was plotted onto a scatter diagram. The points were then joined by a smooth curve, with minimum point (0, 8) and maximum point (6, 16) as shown in the following diagram.

Let the curve in the diagram be y=f(t), where t is the time, measured in months, since Boris first recorded these values.

Boris thinks that f(t) might be modelled by a quadratic function.

Paula thinks that a better model is f(t)=acos(bt)+d, t0, for specific values of a, b and d.

For Paula’s model, use the diagram to write down

The true maximum number of daylight hours was 16 hours and 14 minutes.

Write down one reason why a quadratic function would not be a good model for the number of hours of daylight per day, across a number of years.

[1]
a.

the amplitude.

[1]
b.i.

the period.

[1]
b.ii.

the equation of the principal axis.

[2]
b.iii.

Hence or otherwise find the equation of this model in the form:

f(t)=acos(bt)+d

[3]
c.

For the first year of the model, find the length of time when there are more than 10 hours and 30 minutes of daylight per day.

[4]
d.

Calculate the percentage error in the maximum number of daylight hours Boris recorded in the diagram.

[3]
e.

Markscheme

EITHER
annual cycle for daylight length          R1

OR
there is a minimum length for daylight (cannot be negative)          R1

OR
a quadratic could not have a maximum and a minimum or equivalent          R1


Note: Do not accept “Paula's model is better”.


[1 mark]

a.

4         A1


[1 mark]

b.i.

12         A1


[1 mark]

b.ii.

y=12         A1A1


Note:
Award A1y= (a constant)” and A1 for that constant being 12.

 

[2 marks]

b.iii.

f(t)=-4cos(30t)+12   OR   f(t)=-4cos(-30t)+12         A1A1A1


Note:
Award A1 for b=30 (or b=-30), A1 for a=-4, and A1 for d=12. Award at most A1A1A0 if extra terms are seen or form is incorrect. Award at most A1A1A0 if x is used instead of t.

 

[3 marks]

c.

10.5=-4cos(30t)+12           (M1)


EITHER

t1=2.26585,  t2=9.73414           (A1)(A1)


OR

t1=130cos-138           (A1)

t2=12-t1           (A1)


THEN

9.73414-2.26585

7.47   7.46828 months  (0.622356 years)         A1

 

Note: Award M1A1A1A0 for an unsupported answer of 7.46. If there is only one intersection point, award M1A1A0A0.

 

[4 marks]

d.

16-16+146016+1460×100%           (M1)(M1)

 

Note: Award M1 for correct values and absolute value signs, M1 for ×100.

 

=1.44%   1.43737%          A1

 

[3 marks]

e.

Examiners report

Part (a) indicated a lack of understanding of quadratic functions and the cyclical nature of daylight hours. Some candidates seemed to understand the limitations of a quadratic model but were not always able to use appropriate mathematical language to explain the limitations clearly.

In part (b), many candidates struggled to write down the amplitude, period, and equation of the principal axis.

In part (c), very few candidates recognized that it would be a negative cosine graph here and most did not know how to find the “b” value even if they had originally found the period in part (b). Some candidates used the regression features in their GDC to find the equation of the model; this is outside the SL syllabus but is a valid approach and earned full credit.

In part (d), very few candidates were awarded “follow through” marks in this part. Some substituted 10.5 into their equation rather that equate their equation to 10.5 and attempt to solve it using their GDC to graph the equations or using the “solver” function.

Part (e) was perhaps the best answered part in this question. However, due to premature rounding, many candidates did not gain full marks. A common error was to write the true number of daylight hours as 16.14.

 

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

Syllabus sections

Topic 2—Functions » SL 2.5—Modelling functions
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