18.
[tex]Dane:\\a = 6\frac{m}{s^{2}}\\F = 3 \ N\\Szukane:\\m = ?\\\\Rozwiazanie\\\\F = m\cdot a \ \ /:a\\\\m = \frac{F}{a}\\\\m = \frac{3 \ N}{6\frac{m}{s^{2}}} = \frac{3 \ kg\cdot\frac{m}{s^{2}}}{6\frac{m}{s^{2}}}\\\\\boxed{m = 0,5 \ kg}[/tex]
19.
[tex]Dane:\\v_{o} = 0\frac{m}{s}\\t = 3 \ s\\v = 0,6\frac{m}{s}\\F = 6 \ N\\Szukane:\\m = ?\\\\Rozwiazanie\\\\a = \frac{\Delta v}{t} = \frac{v-v_{o}}{t} = \frac{v}{t} = \frac{0,6\frac{m}{s}}{3 \ s} = 0,2\frac{m}{s^{2}}\\\\m = \frac{F}{a}\\\\m = \frac{6 \ N}{0,2\frac{m}{s^{2}}} = \frac{6 \ kg\cdot\frac{m}{s^{2}}}{0,2\frac{m}{s^{2}}}\\\\\boxed{m = 30 \ kg}[/tex]
