[tex]dane:\\m = 450 \ g = 0,45 \ kg\\E_{k} = 90 \ J = 90 \ kg\cdot\frac{m^{2}}{s^{2}}\\szukane:\\v = ?\\\\Rozwiazanie\\\\E_{k} = \frac{mv^{2}}{2} \ \ /\cdot2\\\\mv^{2} = 2E_{k} \ \ /:m\\\\v^{2} = \frac{2E_{k}}{m}\\\\v = \sqrt{\frac{2E_{k}}{m}}\\\\v = \sqrt{\frac{2\cdot90 \ J}{0,45 \ kg}}} = \sqrt{\frac{180 \ kg\cdot m^{2}/s^{2}}{0,45 \ kg}} = \sqrt{400\frac{m^{2}}{s^{2}}}\\\\v = 20\frac{m}{s}[/tex]
