Final answer:
Acceleration due to gravity affects the projectile throughout its flight; it is never zero and acts in the same direction as the velocity during descent and opposite during ascent.
Step-by-step explanation:
Understanding Projectile Motion on Level Ground
When considering projectile motion on level ground with negligible air resistance and an initial angle that is neither 0° nor 90°, we can answer the following questions:
Is the acceleration ever zero? No, the acceleration due to gravity is always acting on the projectile and it is constant at approximately 9.8 m/s² downward.
Is the acceleration ever in the same direction as a component of velocity? Yes, when the object is moving downwards, the acceleration due to gravity is in the same direction as the vertical component of the velocity.
Is the acceleration ever opposite in direction to a component of velocity? It is opposite when the object is moving upwards, as the acceleration due to gravity slows down the upward motion.
Therefore, while the horizontal velocity component remains constant (assuming no air resistance), the vertical component is continuously affected by gravity, altering the velocity's overall direction during flight.