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Odpowiedź :

[tex]Dane:\\v = 72\frac{km}{h} = 72\cdot\frac{1000 \ m}{3600 \ s} = 20\frac{m}{s}\\s = 300 \ m\\Szukane:\\t = ?\\\\v = \frac{s}{t} \ \ \rightarrow \ \ t = \frac{s}{v}\\\\t = \frac{300 \ m}{20\frac{m}{s}}\\\\\boxed{t = 15 \ s}[/tex]