When a wave passes from one medium to another, its remains constant.
a. velocity
b. wavelength
c. frequency

Answer(b) 60 miles per hour;

Answeroutward from: source;

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