A circular ink-blot grows at the rate of $2$ square cm / sec. Find the rate at which the radius is increasing after $2\frac{6}{11}$ seconds.

The time rate of change of radius of a sphere is $\frac{1}{2\pi }$ . When its radius is $5$ cm. Find the rate of change of the area of the surface of the sphere with time.

A spherical ice-ball is melting in such a way that the radius is decreasing at a constant rate of $0.1 \text{cm}/\text{sec}$. Find the amount of water formed in one second when the radius of the sphere is $7$ cm [Given $\pi =\frac{22}{7}$, specific gravity of ice $=0.9$]