15. (20 p) The relation of total resistance of a ship (R) and other flow parameters are given as: R = f (u, V, L, p, g) where V is the average velocity of the ship, L is the ship length, p is the density, u is the dynamic viscosity and g is the gravitational acceleration. How many non-dimensional groups of it's do you expect for such a problem? Determine the non-dimensional group that includes the dependent variable.