We know that \(v = u + at\), hence
\(0 = u - gT \Rightarrow u = gT\)
When \(v = \frac{u}{2}\), then
\(\frac{u}{2} = u - gt \Rightarrow gt = \frac{u}{2} \Rightarrow gt = \frac{{gT}}{2} \Rightarrow t = \frac{T}{2}\)
Hence at \(t = \frac{T}{2}\), it acquires velocity \(\frac{u}{2}\)
$OA, \,AB,\, BC,\, CD$
($g = 9.8\,m/{s^2}$)