[tex]v = \frac{20km}{h} = \frac{20000m}{3600s} = \frac{200m}{36s} = \frac{50m}{9s} [/tex]
[tex] \frac{50m}{9s} = \frac{500m}{t} [/tex]
[tex]t = \frac{500 \times 9}{50} = 10 \times 9 = 90s[/tex]
[tex]\vec{v}=20 \ km/h \\ d=500 \ m=0,5 \ km \\ \vec{v}=\frac{d}{t} \ \Rightarrow t=\frac{d}{\vec{v}}=\frac{0,5 \ km}{20 \ km/h}=0,025 \ h \\ \Rightarrow \boxed{t=90 \ s}[/tex]
