Approximately (assuming that , the ball was launched from ground level, and that the drag on the ball is negligible.)
Explanation:
Let denote the velocity at which the ball was thrown upward.
If the drag (air friction) on the ball is negligible, the ball would land with a velocity of exactly . The velocity of the ball would be changed from to (such that ) within .
Also because the drag on the ball is negligible, the acceleration of the ball would be . Thus:
.
Since :
.
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The ball reaches maximum height when its velocity is . Apply the SUVAT equation to find the displacement between the original position (ground level, where ) and the max-height position of the ball (where .)