In model X variation of gravitation acceleration g is not considered and along with that no any kinetic energy is supplied to the model , along with that fluid or any other medium resistance is not considered . Similar consideration in Y also only variation of g is considered .
In b part , orbital radius is close to radius of earth or height is small as compared to radius of earth , so there wont be much difference in the value of g , thus only slight changes in the value of answers .
Hope that works if still need help let me know.