Odpowiedź :
[tex]Dane:\\F = 400 \ N\\s = 9 \ km = 9 \ 000 \ m\\t = 2 \ h = 2\cdot3600 \ s = 7200 \ s\\Szukane:\\P = ?\\\\Rozwiazanie\\\\P = \frac{W}{t} = \frac{F\cdot s}{t}\\\\P = \frac{400 \ N\cdot9000 \ m}{7200 \ s}=\frac{36000000 \ J}{7200 \ s}\\\\\boxed{P = 500 \ W}[/tex]