Final answer:
The magnitude of the average acceleration of the second cart is greater than the magnitude of the average acceleration of the first cart because the second cart's speed triples in the same time that the first cart's speed doubles.
Step-by-step explanation:
The magnitude of the average acceleration of the second cart is greater than the magnitude of the average acceleration of the first cart because the second cart's speed triples in the same time that the first cart's speed doubles. Average acceleration is the rate at which the speed of an object changes over time. Since the second cart's speed increases at a faster rate than the first cart's speed, it experiences a greater average acceleration.