0 Question 6 A mechanical question of variable mass. Hint: The following is a physical problem with a body of variable mass which can be solved by means of rst order linear equations. A water drop with an initial mass of [VI grams is falling in the air and it is evaporating with a constant rate of m grains per second. If the resistance of the air is proportional (with a positive constant k) to the speed of the drop1 determine such speed of falling. More hints: use Newton's second law of motion for variable mass: The force on a body is given by the rate of change of momentum. Momentum of a body of mass m and velocity v is p : mu, hence F : (3? Which is the mass of the drop at the time t? Which is the force on the drop (take into account the weight and the resistance of the air)