d
\(\begin{array}{l}
Let'S'\,be\,the\,d{\rm{istance}}\,{\rm{between}}\,{\rm{two}}\,{\rm{ends}}\\
{\rm{'a'}}\,{\rm{be}}\,{\rm{the}}\,{\rm{constant}}\,{\rm{accrleration}}\\
{\rm{As}}\,{\rm{we}}\,{\rm{konw}}\,{{\rm{V}}^2} - {u^2} = 2aS\\
or,\,aS = \frac{{{v^2} - {u^2}}}{2}\\
Let\,V\,be\,velocity\,at\,mid\,po{\mathop{\rm int}} .
\end{array}\)

\(\begin{array}{l}
Therefore,\,V_c^2 - {u^2} = 2a\frac{S}{2}\\
V_c^2 = {u^2} + aS\\
v_c^2 = {u^2} + \frac{{{V^2} - {u^2}}}{2}\\
{V_c} = \sqrt {\frac{{{u^2} + {v^2}}}{2}} 
\end{array}\)