Answer :
As the maximum height is,
[tex]h_{\max }=0.87\text{ m}[/tex]The potential energy of the ball will become zero at the lowest point and kinetic energy will become maximum.
Thus, the height at which the kinetic energy is maximum is,
[tex]h^{\prime}=0_{}[/tex]Thus, the height at which the kinetic energy will become is,
[tex]\begin{gathered} H=\frac{h+h^{\prime}}{2} \\ H=\frac{0.87+0}{2} \\ H=0.435\text{ m} \end{gathered}[/tex]As the kinetic energy is directly proportional to the velocity.
Thus, the velocity become half of its maximum value at 0.435 m.