[tex]Dane:\\F = 20 \ mN = 0,02 \ N\\a = 5\fracPm}{s^{2}}\\Szukane:\\m = ?\\\\\\Z \ II \ zsady \ Newtona:\\\\a = \frac{F}{m} \ \ \rightarrow \ \ m = \frac{F}{a}\\\\m = \frac{0,02 \ N}{5\frac{m}{s^{2}}} = \frac{0,02 \ kg\cdot\frac{m}{s^{2}}}{5\frac{m}{s^{2}}}\\\\\boxed{m = 0,004 \ kg}[/tex]