[tex]Dane:\\m = 800 \ kg\\v_{o} = 15\frac{m}{s}\\t = 20 \ s\\v = 72\frac{km}{h} = 72:3,6\frac{m}{s} = 20\frac{m}{s}\\Szukane:\\F_{w} = ?\\\\Rozwiazanie\\\\a = \frac{\Delta v}{t}= \frac{v-v_{o}}{t} = \frac{20\frac{m}{s}-15\frac{m}{s}}{20 \ s} = \frac{5\frac{m}{s}}{20 \ s} = 0,25\frac{m}{s^{2}}\\\\F_{w} = m\cdot a\\\\F_{w} = 800 \ kg\cdot0,25\frac{m}{s^{2}}}\\\\\boxed{F_{w} = 200 \ N}[/tex]
