Final answer:
The acceleration due to gravity on planet Y is one-ninth the acceleration due to gravity on planet X since planet Y has a radius three times that of planet X.
Step-by-step explanation:
The acceleration due to gravity on the surface of a planet is determined by the planet's mass (M) and radius (R) and is given by the formula g = GM/R^2, where G is the universal gravitational constant. In this question, both planets X and Y have the same mass but planet Y has a radius three times that of planet X. Therefore, by substituting the radius of Y (3R) into the formula, the acceleration due to gravity on planet Y would be g' = GM/(3R)^2 which simplifies to g'= GM/9R² = g/9, where g is the acceleration due to gravity on planet X. Thus, the acceleration due to gravity on planet Y is one-ninth that of planet X.