Final answer:
If the velocity of a car doubles, the momentum of the car also doubles because momentum is directly proportional to velocity, holding mass constant.
Step-by-step explanation:
When the velocity of a car doubles, the momentum of the car also doubles. Momentum is defined as the product of the mass of an object and its velocity. The formula for momentum (p) is given by p = mv, where m is the mass and v is the velocity. If the velocity is doubled, the momentum becomes p = m(2v), which is 2mv. Since the mass of the car remains constant, if we double the velocity, the momentum becomes twice its original value.