The statement, "The net work done by air resistance on the ball during its flight is zero" justify the given condition. Hence, option (c) is correct.
The problem revolves around the concept of gravitation as well as free-fall motion. The explanations for the each of the followings points are:
- The net work done by gravity on the ball during its flight is greater than zero, this statement is not correct because the work done by the gravity is zero, as when the ball comes down its displacement is zero and hence work done is zero.
- The speed at which the ball returns to the point of launch is less than its speed when it was initially launched. This statement is also incorrect, because speed and time are symmetric in both the cases whether the ball goes up or it comes down after being tossed straight up.
- The net work done by air resistance on the ball during its flight is zero. This is the correct statement to justify the given condition. Because due to the air resistance the displacement is zero leading the work to be zero.
- The force of air resistance is directed down-ward both when the ball is rising and when it is falling. This is incorrect statement because force of air-drag will act in direction opposite to the motion. When the ball goes up it acts in the downward direction and when the ball goes down it acts upward.
Thus, we can conclude that the statement, "The net work done by air resistance on the ball during its flight is zero" justify the given condition. Hence, option (c) is correct.
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