[tex]dane:\\s_{c} = 240 \ km\\s_1 = s_2 = \frac{s_{c}}{2} = \frac{240 \ km}{2} =120 \ km\\v_1 = 60\frac{km}{h}\\v_2 = 90\frac{km}{h}\\szukane:\\v_{sr} = ?\\\\Rozwiazanie\\\\v_{sr} = \frac{s_{c}}{t_{c}}\\\\s_{c} = 240 \ km\\\\t = \frac{s}{v}\\\\t_{c} = t_1 + t_2 = \frac{s}{v_1}+\frac{s}{v_2}=\frac{120}{60} + \frac{120}{90} = \frac{6}{3}+\frac{4}{3} = \frac{10}{3} \ [h]\\\\v_{sr} = \frac{240 \ km}{\frac{10}{3} \ h} = \frac{240\cdot3}{10} \ \frac{km}{h} = 72\frac{km}{h}[/tex]
