A) 220 sq. cm/sec
B) 110 sq. cm/sec
C) 35 sq. cm/sec
D) 350 sq. cm/sec
Correct Answer: A
Solution :
Given the rate of increasing the radius \[=\frac{dr}{dt}=3.5cm/sec\] and\[r=10cm\] Area of circle \[=\pi {{r}^{2}}\], \[A=\pi {{r}^{2}}\] Þ \[\frac{dA}{dt}=2\pi r.\frac{dr}{dt}\]Þ \[\frac{dA}{dt}=2\pi \times 10\times 3.5\] Þ \[\frac{dA}{dt}=220c{{m}^{2}}/sec\].
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