[tex]dane:\\s_1 = s\\v_1 = 54\frac{km}{h}\\s_2 = 2s\\v_2 = 18\frac{km}{h}\\s_3 = s\\v_3 = 54\frac{km}{h}\\szukane:\\v_{sr} = ?\\\\Rozwiazanie\\\\v_{sr} = \frac{s_{c}}{t_{c}}\\\\s_{c} = s_1 + s_2 + s_3 = s+2s+s = 4s \ [km]\\\\t = \frac{s}{v}\\\\t_{c} = t_1+t_2+t_3 = \frac{s}{v_1}+\frac{2s}{v_2} + \frac{s}{v_3} = \frac{s}{54}+\frac{2s}{18}+\frac{s}{54} \ [h]=\frac{2s}{54}+\frac{6s}{54} \ [h] = \frac{8s}{54} \ [h] = \frac{4s}{27} \ [h]\\\\v_{sr} = \frac{4s}{\frac{4s}{27}} \ [\frac{km}{h}][/tex]
[tex]v_{sr} = 27\frac{km}{h}[/tex]
