2.
[tex]Dane:\\s_1 = s = 60 \ km\\v_1 = 90\frac{km}{h}\\s_2 = s = 60 \ km\\v_2 = 60\frac{km}{h}\\Szukane:\\v_{sr} = ?\\\\Rozwiazanie\\\\v_{sr} = \frac{s_{c}}{t_{c}}\\\\s_{c} = 2s\\\\t = \frac{s}{t}\\\\t_{c} = t_1+t_2 = \frac{s}{v_1}+\frac{s}{v_2} = \frac{s(v_1+v_2)}{v_1v_2}\\\\v_{sr} =\frac{2s}{\frac{s(v_1+v_2)}{v_1v_2}}=\frac{2v_1v_2}{v_1+v_2}\\\\v_{sr} = \frac{2\cdot90\cdot60}{90+60} \ \ [\frac{km}{h}]\\\\\boxed{v_{sr} = 72\frac{km}{h}}[/tex]
[tex]\underline{Odp. \ C.}[/tex]
3.
A. PRAWDA
[tex]s = 75 \ m, \ \ t = 50 \ s\\v = \frac{s}{t} = \frac{75}{50} = 1,5\frac{m}{s}[/tex]
B. FAŁSZ
[tex]s = 2\cdot75 \ m = 150 \ m[/tex]
C. FAŁSZ
[tex]s_3 = 20 \ m \ \ \ \ \ \ \ \ \ \ \ \ \ s_{5} = 55 \ m\\t_3 = 20 \ s \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ t_{5} = 55 \ s\\v_3 = \frac{2}{20} = 1\frac{m}{s} \ \ \ \ \ \ \ \ v_{5} = \frac{55}{55} = 1\frac{m}{s}[/tex]
D. PRAWDA
[tex]t_{z} = t_2+t_4 =10 \ s + 40 \ s = 50 \ s[/tex]
4.
[tex]Dane:\\v_{o} = 0\\t = 0,4 \ s\\v = 4\frac{m}{s}\\Szukane:\\h = ?\\\\Rozwiazanie\\\\h = \frac{1}{2}at^{2}\\\\a = \frac{\Delta v}{t} = \frac{v-v_{o}}{t} = \frac{v}{t} = \frac{4\frac{m}{s}}{0,4 \ s} = 10\frac{m}{s^{2}}\\\\h = \frac{1}{2}\cdot10\frac{m}{s^{2}}\cdot(0,4 \ s)^{2}\\\\\boxed{h = 0,8 \ m}[/tex]
