Answer: Apparently option B. an increase in Uk and/or C. an increase in the normal force
Explanation: the formula for force of kinetic friction is given by Fk = μk×η
Fk meaning the very force of kinetic friction
μk meaning the coefficient of kinetic friction
η meaning the normal force
The coefficient of kinetic friction (μk) will change based up on the type of material which the surface of the objects in motion are made of. Changing surfaces will alter μk.
Although the normal force will depend on the mass of the object in motion, and it can affect the force of kinetic friction as well. Putting more mass into the object will increase force of kinetic friction.
