The statement that best substantiates Newton's second law of motion, \( F = ma \), is:
Applying double the force to the car will lead to its deceleration at a rate twice as fast.
This is consistent with the principle behind Newton’s second law, which states that the force acting on an object is equal to the mass of that object multiplied by its acceleration. Therefore, if the mass remains constant (as is the case with the car), increasing the force applied (in this case, by doubling it) will result in a proportional increase in acceleration (or deceleration, when considering braking).