There is a small hole of radius r in a hollow sphere, which is immersed in a liquid. Upto what maximum depth it can be immersed so that liquid may not enter in it? Density of liquid is d and surface tension is T.

h = 4T/dgr

Explanation:

Using Laplace law for spherical bubble, the pressure difference P'- P = 4T/r where T = surface tension and r = radius of sphere.

Now, the pressure difference on the hollow sphere P' - P = dgh where d = density of liquid, g = acceleration due to gravity and h = maximum depth to which sphere must be immersed.  

So dgh = 4T/r

h = 4T/dgr

this could be newton#'s law of cooling. the cooling curve is exponential