Final answer:
If an object's velocity is doubled, its momentum is also doubled, given that the mass is constant. Momentum is directly proportional to an object's velocity, which means that any change in velocity will result in a proportional change in momentum.
Step-by-step explanation:
If an object's velocity is doubled, its momentum is also doubled. Momentum, which is a product of an object's mass and its velocity, is directly proportional to velocity when the mass is constant. Therefore, if the velocity is doubled, the momentum would be doubled as well, assuming mass remains unchanged.
Referring to the provided information - when the velocity of a wave is doubled, it affects the change in momentum. Given that momentum is dependent on both mass and velocity (p=mv), and mass remains constant, the momentum is directly proportional to the velocity (Option a). Hence, the correct answer to the question is that the momentum is doubled (Option 4).