Đáp án:
\(\begin{array}{l}
t = 6,562s\\
v' = 20,62m/s\\
{v_{tb}} = 4,7623m/s
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
mgh + \frac{1}{2}mv_0^2 = mgh'\\
10.20 + \frac{1}{2}{.5^2} = 10.h'\\
h' = 21,25m\\
a = \frac{{{v^2} - v_0^2}}{{2(h' - h)}} = \frac{{{0^2} - {5^2}}}{{2(21,25 - 10)}} = - \frac{{10}}{9}m/{s^2}\\
a = \frac{{v - {v_0}}}{t}\\
\frac{{ - 10}}{9} = \frac{{0 - 5}}{t}\\
t = 4,5s\\
t' = \sqrt {\frac{{2h'}}{g}} = \sqrt {\frac{{2.21,25}}{{10}}} = 2,062s\\
t = t + t' = 4,5 + 2,062 = 6,562s\\
v' = gt = 10.2,062 = 20,62m/s\\
{v_{tb}} = \frac{{h + h'}}{{t}} = \frac{{10 + 21,25}}{{6,562}} = 4,7623m/s
\end{array}\)