9. (16 pt) Jenny tried to push a 40. kg box to cross the room. The box started to move when her pushing force is increased to 120 N. After that, Jenny kept push the box with a constant force of 120 N. The graph below records the friction force between the box and the floor over time. Friction 120 N 100 N a) What is the weight of the box? b) What is the maximum static friction of the floor? What is the coefficient of the static friction? c) What is the kinetic friction of the floor? What is the coefficient of the kinetic friction? d) Once the box starts to move, what is the acceleration of the box? Draw a free-body diagram of the box 4