Choosing which direction counts as positive in a projectile problem affects:

1. A coordinate system is a description rather than a physical fact. 2. If you arrange the coordinate system such that the downwards direction is positive, then acceleration due to gravity takes a positive value. 3. The same fall would carry a negative sign under the opposite convention. 4. Where the ball lands and how long it takes do not depend on that choice. 5. The magnitude of g is a property of the Earth rather than of the axes. _Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 3 'Two-Dimensional Kinematics', sections 3.1-3.4_