[tex]dane:\\v = 10\frac{m}{s}\\E_{k} = 0,5 \ kJ = 0,5\cdot1000 \ J = 500 \ J\\szukane:\\m = ?\\\\E_{k} = \frac{mv^{2}}{2} \ \ /\cdot\frac{2}{v^{2}}\\\\m = \frac{2E_{k}}{v^{2}}\\\\m = \frac{2\cdot500 \ J}{(10\frac{m}{s})^{2}} = \frac{1000 \ kg\cdot\frac{m^{2}}{s^{2}}}{100\frac{m^{2}}{s^{2}}} = 10 \ kg}\\\\\underline{Odp. \ B. \ 10 \ kg}[/tex]
