Final answer:
The optimal angle for a projectile's maximum range is 45 degrees, while the actual angle used is 60 degrees according to the given options, though 45 degrees is generally better for maximizing range.
Step-by-step explanation:
The optimal angle for launching a projectile to achieve maximum range on level ground, without considering air resistance, is 45 degrees. This principle comes from the physics of projectile motion, where the relationship between launch angle and range is symmetrical around 45 degrees.
Given the choices in the question, the correct answer is option (a), where the optimal angle is 45 degrees, but the actual angle used is 60 degrees. This may not be the most efficient choice if the goal is to maximize the range of the projectile, as the range is also zero at 90 degrees. The angles mentioned in the other reference entries (30.1 degrees, 48.7 degrees, etc.) correspond to specific contexts or experimental results that are different from the general principle of projectile motion.