A balloon, which always, remains spherical, has a variable radius. Find the rate at which its volume is increasing with respect to its radius when the radius is 7cm.

Explanation

The volume of a sphere (V) with radius (r) is given by `V=4/3pir^3`

Rate of change of volume (V) with respect to its radius (r) is given by,

`((dV)/dr)=(d/dr)(4/3pir^3)=4/3pi(3pir^2)=4pir^2`

when radius =10cm,

`((dV)/dr)=4pi(10)^2=400pi cm^2`