You push on a refrigerator with a force of 20 N and cause the refrigerator to accelerate at 2 m/s/s. What is the refrigerator's mass in kg

The answer is trial 3.

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other