[tex]dane:\\m = 400 \ kg\\E_{k} = 20 \ kJ = 20 \ 000 \ J\\szukane:\\v = ?\\\\E_{k} = \frac{mv^{2}}{2} \ \ /\cdot\frac{2}{m}\\\\v^{2} = \frac{2E_{k}}{m}\\\\v = \sqrt{\frac{2E_{k}}{m}}\\\\v = \sqrt{\frac{2\cdot20000 \ J}{400 \ kg}} = \sqrt{\frac{2\cdot20000 \ kg\cdot\frac{m^{2}}{s^{2}}}{400 \ kg}}} = \sqrt{100\frac{m^{2}}{s^{2}}}\\\\v = 10\frac{m}{s}[/tex]
