A) \[\pi \,c{{m}^{2}}/s\]
B) \[2\pi \,c{{m}^{2}}/s\]
C) \[10\pi \,c{{m}^{2}}/s\]
D) None of these
Correct Answer: D
Solution :
\[\frac{dr}{dt}=3\], we have \[S=\pi {{r}^{2}}\Rightarrow \frac{dS}{dt}=2\pi r\frac{dr}{dt}\] Þ \[{{\left( \frac{dS}{dt} \right)}_{r=10}}=2.\pi \times 10\times 3=60\,\pi \,c{{m}^{2}}/sec.\]
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