A train, originally of mass M, is traveling on a frictionless straight horizontal track with constant speed v. Snow starts to fall vertically and sticks to the train at a rate of \rho, where \rho has units of kilograms per second. The train’s engine keeps the train moving at constant speed v as snow accumulates on the train. The rate at which the kinetic energy of the train and snow increases is
Answer Choices
A. 0
B. M g v
C. \frac{1}{2} M v^{2}
D. \frac{1}{2} \rho v^{2}
E. \rho v^{2}