Final answer:
Doubling the coefficient of friction would cause the car to decelerate more quickly, while doubling the initial velocity would result in a longer stopping distance. Combining both effects would further increase the deceleration and shorten the stopping distance.
Step-by-step explanation:
In this case, we can analyze the effect of doubling the coefficient of friction and the initial velocity separately and then combine the effects for both doubled:
(a) Doubling the coefficient of friction would increase the friction force acting on the car. This increased friction force would cause the car to decelerate more quickly and come to a stop in a shorter distance.
(b) Doubling the initial velocity would increase the kinetic energy of the car. This increased kinetic energy would cause the car to take longer to come to a stop, resulting in a longer stopping distance.
(c) Combining both effects, doubling both the coefficient of friction and the initial velocity would result in a greater increase in the friction force and kinetic energy. The car would decelerate even more quickly and come to a stop in an even shorter distance compared to just doubling the coefficient of friction or the initial velocity individually.