[tex]dane:\\m = 600 \ kg\\v_{o} = 0\\t = 40 \ s\\v = 20\frac{m}{s}\\szukane:\\F = ?\\\\a = \frac{\Delta v}{t} = \frac{v-v_{o}}{t} = \frac{v}{t} = \frac{20\frac{m}{s}}{40 \ s} = 0,5\frac{m}{s^{2}}\\\\F = m\cdot a\\\\F = 600 \ kg\cdot0,5\frac{m}{s^{2}}\\\\F = 300 \ N[/tex]