[tex]dane:\\s_1 = 7 \ km\\v_1 = 15\frac{km}{h}\\s_2 = 21 \ m\\v_2 = 20\frac{km}{h}\\szukane:\\v_{sr} = ?[/tex]
Rozwiązanie
Prędkość średnia to iloraz całkowitej drogi do całkowitego czasu trwania ruchu.
[tex]v_{sr} = \frac{s_{c}}{t_{c}}[/tex]
[tex]s_{c} = s_1 + s_2 = 7 \ km + 21 \ km = 28 \ km\\\\t = \frac{s}{v}\\\\t_{c} = t_1 + t_2 = \frac{s_1}{v_1} + \frac{s_2}{v_2} = \frac{7 \ km}{15\frac{km}{h}} + \frac{21 \ km}{20\frac{km}{h}} = \frac{28+63}{60} \ h = \frac{91}{60} \ h\\\\v_{sr} = \frac{28 \ km}{\frac{91}{60}h} =\frac{28\cdot60}{91} \ \frac{km}{h}\approx18,46\frac{km}{h}[/tex]
