[tex]Dane:\\s_1 = 120 \ km\\v_1 = 120\frac{km}{h}\\s_2 = 100 \ km\\v_2 = 60\frac{km}{h}\\Szukane:\\v_{sr} = ?\\\\Rozwiazanie\\\\v_{sr} = \frac{s_{c}}{t_{c}}\\\\s_{c} = s_1+s_2 = 120 \ km +100 \ km = 220 \ km\\\\t = \frac{s}{v}\\\\t_1 = \frac{s_1}{v_1} = \frac{120 \ km}{120\frac{km}{h}} = 1 \ h\\\\t_2 = \frac{s_2}{v_2} = \frac{100 \ km}{60\frac{km}{h}} = \frac{5}{3} \ h\\\\t_{c} = t_1+t_2 = 1 \ h + \frac{5}{3} \ h = \frac{8}{3} \ h\\\\v_{sr} = \frac{220 \ km}{\frac{8}{3}h}\\\\\boxed{v_{sr} = 82,5\frac{km}{h}}[/tex]
