Final answer:
The measurement of angle a (∠a) can only be determined with specific context, which is not provided in the original question. However, in physics, a projectile's range is zero at 90°, the optimum angle for maximum distance is 45°, and the angle between tangential velocity and centripetal force vectors is 90°.
Step-by-step explanation:
The measurement of ∠a depends on the context provided within the projectile motion and angular motion exercises discussed. From the provided options, we can determine the measurement of ∠a in various scenarios:
- For what angle of a projectile is its range equal to zero? The range of a projectile is zero at an angle of 90°.
- What is the optimum angle at which a projectile should be launched in order to cover the maximum distance? The optimum angle for maximum distance is 45°.
- What is the angle formed between the vectors of tangential velocity and centripetal force? This angle is 90° since these vectors are perpendicular to each other.
- If a projectile is launched on level ground, the launch angle that maximizes the range of the projectile is 45°.
Without additional context for ∠a specifically, we cannot definitively answer the original question; however, the provided answer choices suggest different angular measurements based on various scenarios within physics.