A) i. The Amnesia roller coaster accelerates at a rate of 35 m/s? How long does it take to reach its maximum speed of 50 m/s when it is starting from rest?

As newton's first law states a object in motion stays in motion

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