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Date May 2021 Marks available 1 Reference code 21M.2.AHL.TZ1.9
Level Additional Higher Level Paper Paper 2 Time zone Time zone 1
Command term Show that Question number 9 Adapted from N/A

Question

Two boats A and B travel due north.

Initially, boat B is positioned 50 metres due east of boat A.

The distances travelled by boat A and boat B, after t seconds, are x metres and y metres respectively. The angle θ is the radian measure of the bearing of boat B from boat A. This information is shown on the following diagram.

Show that y=x+50cotθ .

[1]
a.

At time T, the following conditions are true.

Boat B has travelled 10 metres further than boat A.
Boat B is travelling at double the speed of boat A.
The rate of change of the angle θ is -0.1 radians per second.

Find the speed of boat A at time T.

[6]
b.

Markscheme

tanθ=50y-x  OR  cotθ=y-x50        A1

y=x+50cotθ        AG

 

Note: y-x may be identified as a length on a diagram, and not written explicitly.

 

[1 mark]

a.

attempt to differentiate with respect to t         (M1)

dydt=dxdt-50cosecθ2dθdt        A1

attempt to set speed of B equal to double the speed of A        (M1)

2dxdt=dxdt-50cosecθ2dθdt

dxdt=-50cosecθ2dθdt        A1

θ=arctan5=1.373=78.69°  OR  cosec2θ=1+cot2θ=1+152=2625        (A1)

 

Note: This A1 can be awarded independently of previous marks.

 

dxdt=-502625×-0.1

So the speed of boat A is 5.2ms-1        A1

 

Note: Accept 5.20 from the use of inexact values.

 

[6 marks]

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Topic 3— Geometry and trigonometry » AHL 3.9—Reciprocal trig ratios and their pythagorean identities. Inverse circular functions
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Topic 3— Geometry and trigonometry

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