1.

The radius of a sphere is changing at the rate of0.1 cm/sec. The rate of change of its surface area when the radius is 200 cmis(a)cm2/sec (b)cm2/sec(c)cm2/sec (d)cm2/secA. `8pi cm^(2)//sec`B. `12pi cm^(2)//sec`C. `160pi cm^(2)//sec`D. `200cm^(2)//sec`

Answer» Correct Answer - C
Let r be the radius and S be the surface area of the sphere at any time t. Then,
`S=4pir^(2)`
`implies (dS)/(dt)=8pir(dr)/(dt)`
`implies ((dS)/(dt))_(r=200)=8pixx200xx0.1=160 pi cm^(2)//sec`


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