In a one dimensional problem, two boxes are heading toward each other. Box A has a mass of 20 kg and has an initial velocity of +10 m/s. Box B has a mass of 30 kg and has an initial velocity of -5 m/s. a) If the collision is perfectly inelastic, what is the final velocity of Box A and B? b) If the collision is not perfect and the velocity of Box A after the collision is -9 m/s, what is the final velocity of Box B?