A circular ornamental garden pond, of radius 2 metres, has weed starting to grow and cover its surface.
As the weed grows, it covers an area of \(A\) square metres. A simple model assumes that the weed grows so that the rate of increase of its area is proportional to \(A\).
- Show that the area covered by the weed can be modelled by
$$A = Be^{kt}$$
where \(B\) and \(k\) are constants and \(t\) is time in days since the weed was first noticed. [4 marks]
- When it was first noticed, the weed covered an area of 0.25 m². Twenty days later the weed covered an area of 0.5 m²
- State the value of \(B\). [1 mark]
- Show that the model for the area covered by the weed can be written as
$$A = 2^{\frac{t}{20} - 2}$$ [4 marks]
- How many days does it take for the weed to cover half of the surface of the pond? [2 marks]
- State one limitation of the model. [1 mark]
- Suggest one refinement that could be made to improve the model. [1 mark]