[tex]v_1 = 15\frac{km}{h}\\t_1 = \frac{2}{3} \ h\\t_2 = \frac{1}{2} \ h\\v_2 = ?\\\\\\s = v_1\cdot t_1\\oraz\\s = v_2\cdot t_2\\\\v_2\cdot t_2 = v_1\cdot t_1 \ \ \ |:t_2\\\\v_2 = v_1\cdot\frac{t_1}{t_2}\\\\v_2 =15\frac{km}{h}\cdot\frac{\frac{2}{3}h}{\frac{1}{2}h} = 15\frac{km}{h}\cdot\frac{2}{3}\cdot2=5\frac{km}{h}\cdot4\\\\\boxed{v_2 = 20\frac{km}{h}}[/tex]
[tex]\underline{Odp. \ B.}[/tex]
