Final answer:
The minimum range for friendly fire in the 90-degree mode is zero. This occurs when a projectile is launched at either 90°, which sends it straight up, or at 0°, which does not allow for any horizontal motion.
Step-by-step explanation:
The question revolves around the concept of projectile motion, particularly focusing on the angle of launch that results in a specific range of outcomes. In the context of projectile motion without air resistance, the range of the projectile is maximum at an angle of 45°. It is noted that for projectiles launched at two angles that add up to 90°, the ranges are identical.
The angle that would result in a range of zero can be identified through the options provided in the multiple-choice question. The correct answer to the question is c. 90° or 0° because a projectile launched straight up (90°) would come straight down, and a projectile launched at 0° angle would have no vertical component to its motion and thus would not cover any horizontal distance.