Mary applies a force of 70 N to push a box with an acceleration of 0.41 m/sz. When she increases the pushing force to 78 N, the box's acceleration changes to 0.66 m/sz. There is a constant friction force present between the floor and the box (a) What is the mass of the box in kilograms? _./kg (b) What is the coefficient of kinetic friction between the floor and the box? _x What is the relation between friction force and normal force? Did you apply Newton's Second Law to motion in the vertical direction