[tex]Dane:\\t= 4 \ s\\s = 40 \ m\\v = 0\\Szukane:\\v_{o} = ?\\\\Rozwiazanie\\\\s = v_{o}t - \frac{1}{2}at^{2}\\\\a = \frac{v_{o}}{t}\\\\zatem\\\\s = v_{o}t - \frac{1}{2}\cdot\frac{v_{o}}{t}\cdot t^{2}\\\\s = v_{o}t - \frac{1}{2}v_{p}t\\\\s = \frac{1}{2}v_{o}t \ \ /\cdot 2\\\\v_{o}t = 2s \ \ /:t\\\\v_{o} = \frac{2s}{t}\\\\v_{o} = \frac{2\cdot40 \ m}{4 \ s}\\\\\boxed{v_{o} = 20\frac{m}{s}}[/tex]
