[tex]Dane:\\v_{o} = 0\\t = 2 \ s\\s = 20 \ m\\Szukane:\\v = ?\\\\Rozwiazanie\\\\\underline{v = a\cdot t}\\\\ale\\\\s = \frac{at^{2}}{2} \ \ |\cdot\frac{2}{t^{2}}\\\\a = \frac{2s}{t^{2}} = \frac{2\cdot20 \ m}{(2 \ s)^{2}} =\frac{40 \ m}{4 \ s^{2}} = 10\frac{m}{s^{2}}\\\\v =10\frac{m}{s^{2}}\cdot2 \ s\\\\\boxed{v = 20\frac{m}{s}}[/tex]