Final answer:
The coefficient of kinetic friction decreases with speed.The coefficient of kinetic friction remains constant and does not depend on the relative speed at which the two surfaces are moving past each other.
Step-by-step explanation:
The coefficient of kinetic friction depends on the speed of two surfaces in contact. As the relative speed between the surfaces increases, the magnitude of the coefficient of kinetic friction decreases.
For example, when you rub your hands together slowly, the frictional force is stronger than when you rub them together quickly. This is because the roughness and irregularities of the surfaces come into contact for a longer time with slower motion, leading to a higher coefficient of kinetic friction.
Therefore, the correct answer is c) Yes, it decreases with speed.