A spherical rain drop evaporates at a rate proportional to its surface area. If its radius is originally 3 mm and after 1 hour i t is reduced to 2 mm, find an expression for radius of rain drop at any time.

A spherical bubble is decreasing in volume at the rate of 2cm^3//sec . Find the rate of which the suraface area is diminishing when the radius is 3 cm.

The volume of spherical ballon being inflated at a constant rate. If initially its radius is 3 units and after 3 seconds it is 6 units. Find the radius of the balloon after t seconds.

If the volume of a sphere is increasing at a constant rate, then the rate at which its radius is increasing is a)a constant b)proportional to the radius c)inversely proportional to the radius d)inversely proportional to its surface area

Find the rate of change of the area of a circle with respect to its radius r when r = 3 cm.