[tex]Dane:\\v = 10\frac{m}{s}\\E_{k} = 1 \ kJ = 1000 \ J\\Szukane:\\m = ?[/tex]
Korzystamy ze wzoru na energię kinetyczną:
[tex]E_{k} = \frac{mv^{2}}{2} \ \ \ |\cdot2\\\\mv^{2} = 2E_{k} \ \ \ |:v^{2}}\\\\m = \frac{2E_{k}}{v^{2}}\\\\m = \frac{2\cdot1000 \ J}{(10\frac{m}{s})^{2}} = \frac{2000 \ kg\cdot\frac{m^{2}}{s^{2}}}{100\frac{m^{2}}{s^{2}}}\\\\\boxed{m = 20 \ kg}[/tex]
