Chamando de A o ponto no alto do prédio e B o ponto no solo, temos:
[tex]E_{M_A}=E_{M_B}\\\\
E_{P_A}+E_{C_A}=E_{P_B}+E_{C_B}\\\\
E_{P_A}=E_{C_B}\\\\
E_{C_B}=m\cdot g\cdot h\\\\
E_{C_B}=2,5\cdot10\cdot30\\\\
\boxed{E_{C_B}=750\;J}[/tex]
[tex]E_{C_B}=\dfrac{mV^2}{2}\\\\
750=\dfrac{2,5\cdot V^2}{2}\\\\
2,5\cdot V^2=1500\\\\
V^2=\dfrac{1500}{2,5}\\\\
V^2=600\\\\
V=\sqrt{600}\\\\
\boxed{V=10\sqrt{6}\;m/s}[/tex]