Đáp án:
a,$175m$
b.$20\left( {m/s} \right)$
Giải thích các bước giải:
$\begin{array}{l}
a.{v_A} = 36km/h = 10m/s\\
a = \frac{{{v_B} - {v_A}}}{{\Delta t}} = \frac{{25 - 10}}{{10}} = 1,5\left( {m/{s^2}} \right)\\
v_B^2 - v_A^2 = 2as\\
\Rightarrow {25^2} - {10^2} = 2.1,5.s\\
\Rightarrow s = 175m = AB\\
b.{t_{BC}} = \frac{{BC}}{{{v_B}}} = \frac{{125}}{{25}} = 5\left( s \right)\\
{v_{tbAC}} = \frac{{AB + BC}}{{{t_{AB}} + {t_{BC}}}} = \frac{{175 + 125}}{{10 + 5}} = 20\left( {m/s} \right)
\end{array}$
