Answer:
Step-by-step explanation:
All of the above.
Certainly a coaster could be designed without considering any one item of mass, gravity, or rates of direction change, but the success of the ride would be highly suspect.
Ignoring mass (of cars and/or riders) could lead to support members not being strong enough.
Ignoring rates of change of direction could lead to support members not being strong enough or make the forces on the riders uncomfortable.
Ignoring gravity could lead to support members not being strong enough or make the forces on the riders uncomfortable.