You pull horizontally on a 50-kg crate with a force of 500 N and the friction force on the crate is 100 N. There is also air resistance of 20 N. What is the acceleration in the x direction of the crate?

Cin carbonh in hydrogeno in oxygen

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