Final answer:
If the Earth's radius were tripled, a person's weight would decrease by a factor of 9 due to the inverse square law of gravitation.
Step-by-step explanation:
The weight of a person on Earth is determined by the gravitational force exerted by the Earth's mass. If the radius of the Earth were tripled and its mass remained the same, the person's weight would change due to the inverse square law of gravitation. According to this law, gravitational force is inversely proportional to the square of the distance between the two objects (in this case, the distance being the Earth's radius). Therefore, if the radius of the Earth were tripled, the weight of a person would decrease by a factor of (3)^2, which is 9. The correct answer is that a person's weight would decrease by a factor of 9 if the radius of the Earth were tripled.