[tex]dane:\\W = 4 \ J\\m = 2 \ kg\\szukane:\\v = ?\\\\\\W = E_{k} = \frac{mv^{2}}{2}\\\\W = \frac{mv^{2}}{2} \ \ /\cdot\frac{2}{m}\\\\v^{2} = \frac{2W}{m}\\\\v = \sqrt{\frac{2W}{m}}\\\\v = \sqrt{\frac{2\cdot4 \ J}{2 \ kg}} = \sqrt{\frac{4 \ kg\cdot\frac{m^{2}}{s^{2}}}{kg}} = \sqrt{4\frac{m^{2}}{s^{2}}}\\\\\underline{v = 2\frac{m}{s}}\\\\Odp. \ B.[/tex]
