Đáp án:
17. D
18 B
19B
Giải thích các bước giải:
\(\begin{array}{l}
17.\\
a = \frac{{{v^2} - v_0^2}}{{2s}} = \frac{{0 - {{10}^2}}}{{2.12}} = - \frac{{25}}{6}m/{s^2}\\
{F_h} = - ma = - 300.\frac{{ - 25}}{6} = 1250N\\
D\\
18.\\
{W_d} = \frac{1}{2}m{v^2} = \frac{1}{2}{50.20^2} = 10000J = 10kJ\\
B\\
19.\\
{W_d} = \frac{1}{2}m{v^2}\\
{W_d}' = \frac{1}{2}m'v{'^2} = \frac{1}{2}.\frac{m}{4}.{(2v)^2} = \frac{1}{2}m{v^2} = {W_d}\\
B
\end{array}\)
