Final answer:
In questions about motions under gravity, assume all objects fall with the same constant acceleration due to gravity, g, of about 9.80 m/s², when air resistance and friction are negligible, and that motion is one-dimensional with a downward acceleration.
Step-by-step explanation:
When answering questions about motions under gravity, you can always assume that all objects fall toward the center of Earth with the same constant acceleration due to gravity, if air resistance and friction are negligible. This constant acceleration, denoted as g, is approximately 9.80 m/s². It is crucial to remember that the direction of the acceleration due to gravity is always downward, towards the Earth's center, which defines what we call vertical. The application of kinematics to motions under gravity assumes one-dimensional motion, which means the motion has constant acceleration of magnitude g and the initial velocity of a dropped object is zero.