2025 CGSS PRELIMS P1 Q13
2025 CGSS PRELIMS P1 Q13
Secondary 4
5 marks
A circular patch of water of negligible thickness is evaporating. The radius of the patch, \(r\) cm is decreasing at a constant rate of 0.2 cm/s. Find the rate of change of the area of this patch, \(A\) cm\(^2\) when the area of the patch is \(225\pi\) cm\(^2\).[5]
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Answer:\(\frac{\mathrm dA}{\mathrm dt}=-6\pi\text{ cm}^2\text{/s}\approx-18.8\text{ cm}^2\text{/s}\)
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