Final answer:
The speed of a projectile that is launched vertically upward and is affected by air resistance upon returning to its starting point will be less than its initial speed due to the decelerating effect of air resistance during both the ascent and descent. Option A is correct.
Step-by-step explanation:
When a projectile is launched vertically upward and air resistance affects its motion, the speed upon returning to its starting point is less than 50 m/s. Unlike in a vacuum where there would be no air resistance and the speed would be the same going up and coming down (50 m/s), air resistance decelerates the projectile more as it ascends and continues to act against it as it descends. Therefore, the speed is reduced both going up and coming down.
Air resistance essentially removes energy from the system, which results in a lower impact speed compared to the initial launch speed. When air resistance cannot be neglected, it always acts in the direction opposite of the motion, thus slowing down the projectile whether it is ascending or descending.
When a projectile is launched vertically upward, its speed upon returning to its starting point would be less than 50 m/s if air resistance affects its motion. This is because air resistance acts in the opposite direction to the motion of the projectile, causing it to slow down.
As the projectile moves upward, the force of air resistance opposes its upward motion, decreasing its speed. When the projectile reaches its maximum height and starts to fall back down, air resistance continues to slow it down.
Therefore, the projectile will have a lower speed than its initial velocity of 50 m/s when it returns to its starting point.