A raindrop initially has mass M_0 = 0.277~\mathrm{g}M 0 =0.277 g and, due to gravity, starts falling from rest through a cloud. One way to model the growth of a raindrop is to assume that its mass grows proportionally to the product of its instantaneous mass and velocity, according to the following equation \dfrac{dM}{dt} = kMV. dt dM =kMV. Here, kk is a constant of proportionality, which we take to be k = 6.99~\mathrm{m}^{-1}.k=6.99 m −1 . What is the speed of the rain drop when its mass has doubled its initial value?